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(Circulation. 2005;111:e394-e434.)
© 2005 American Heart Association, Inc.

AHA Scientific Statement

Infective Endocarditis

Diagnosis, Antimicrobial Therapy, and Management of Complications: A Statement for Healthcare Professionals From the Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease, Council on Cardiovascular Disease in the Young, and the Councils on Clinical Cardiology, Stroke, and Cardiovascular Surgery and Anesthesia, American Heart Association: Endorsed by the Infectious Diseases Society of America

Larry M. Baddour, MD, Chair; Walter R. Wilson, MD; Arnold S. Bayer, MD; Vance G. Fowler, Jr, MD, MHS; Ann F. Bolger, MD; Matthew E. Levison, MD^*; Patricia Ferrieri, MD; Michael A. Gerber, MD; Lloyd Y. Tani, MD; Michael H. Gewitz, MD; David C. Tong, MD; James M. Steckelberg, MD; Robert S. Baltimore, MD; Stanford T. Shulman, MD; Jane C. Burns, MD; Donald A. Falace, DMD; Jane W. Newburger, MD, MPH; Thomas J. Pallasch, DDS, MS; Masato Takahashi, MD; Kathryn A. Taubert, PhD

Correspondence to Kathryn A. Taubert, PhD, FAHA, American Heart Association, 7272 Greenville Ave, Dallas, TX 75231. E-mail Ktaubert{at}heart.org

	Abstract

Top Abstract Introduction Evidence-Based Scoring System Diagnosis Antimicrobial Therapy Staphylococci Enterococci HACEK Microorganisms Enterobacteriaceae Pseudomonas Species Unusual Gram-Negative Bacteria Culture-Negative Endocarditis Fungi Endocarditis in IDUs Etiology of Endocarditis in... Complications and Their... Outpatient Therapy Care at Completion of... References

 
Background— Despite advances in medical, surgical, and critical care interventions, infective endocarditis remains a disease that is associated with considerable morbidity and mortality. The continuing evolution of antimicrobial resistance among common pathogens that cause infective endocarditis creates additional therapeutic issues for physicians to manage in this potentially life-threatening illness.

Methods and Results— This work represents the third iteration of an infective endocarditis "treatment" document developed by the American Heart Association under the auspices of the Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease, Council on Cardiovascular Disease of the Young. It updates recommendations for diagnosis, treatment, and management of complications of infective endocarditis. A multidisciplinary committee of experts drafted this document to assist physicians in the evolving care of patients with infective endocarditis in the new millennium. This extensive document is accompanied by an executive summary that covers the key points of the diagnosis, antimicrobial therapy, and management of infective endocarditis. For the first time, an evidence-based scoring system that is used by the American College of Cardiology and the American Heart Association was applied to treatment recommendations. Tables also have been included that provide input on the use of echocardiography during diagnosis and treatment of infective endocarditis, evaluation and treatment of culture-negative endocarditis, and short-term and long-term management of patients during and after completion of antimicrobial treatment. To assist physicians who care for children, pediatric dosing was added to each treatment regimen.

Conclusions— The recommendations outlined in this update should assist physicians in all aspects of patient care in the diagnosis, medical and surgical treatment, and follow-up of infective endocarditis, as well as management of associated complications. Clinical variability and complexity in infective endocarditis, however, dictate that these guidelines be used to support and not supplant physician-directed decisions in individual patient management.

Key Words: AHA Scientific Statements • endocardium • drugs • echocardiography • infection

	Introduction

Top Abstract Introduction Evidence-Based Scoring System Diagnosis Antimicrobial Therapy Staphylococci Enterococci HACEK Microorganisms Enterobacteriaceae Pseudomonas Species Unusual Gram-Negative Bacteria Culture-Negative Endocarditis Fungi Endocarditis in IDUs Etiology of Endocarditis in... Complications and Their... Outpatient Therapy Care at Completion of... References

 

Introduction...e395

Evidence-Based Scoring System...e396

Level of Evidence...e396

Diagnosis...e396

Echocardiography...e399

Repeat Echocardiography...e400

Intraoperative Echocardiography...e400

Echocardiography at Completion of Therapy...e400

Antimicrobial Therapy...e400

Antimicrobial Treatment Perspectives...e400

Overview of Viridans Group Streptococci, Streptococcus bovis, Abiotrophia defectiva, Granulicatella Species, and Gemella Species...e401

Highly Penicillin-Susceptible Viridans Group Streptococci and S bovis (MIC 0.12 µg/mL)...e402

Viridans Group Streptococci and S bovis With Penicillin MIC >0.12 µg/mL to 0.5 µg/mL...e403

Abiotrophia defectiva and Granulicatella Species (Formerly Known as Nutritionally Variant Streptococci), Gemella Species, and Viridans Group Streptococci With Penicillin MIC >0.5 µg/mL...e403

Endocarditis of Prosthetic Valves or Other Prosthetic Material Caused by Viridans Group Streptococci and S bovis...e403

Streptococcus pneumoniae, Streptococcus pyogenes, and Groups B, C, and G Streptococci...e403

Staphylococci...e404

Staphylococcus aureus...e404

Coagulase-Negative Staphylococci...e404

Endocarditis in the Absence of Prosthetic Valves Caused by Staphylococci...e404

Right-Sided Endocarditis in IDUs...e404

Endocarditis in Non-IDUs...e405

Endocarditis in the Presence of Prosthetic Valves or Other Prosthetic Material Caused by Staphylococci...e407

Coagulase-Negative Staphylococci...e407

Staphylococcus aureus...e407

Enterococci...e407

Enterococci Susceptible to Penicillin, Vancomycin, and Aminoglycosides...e408

Enterococci Susceptible to Penicillin, Streptomycin, and Vancomycin and Resistant to Gentamicin...e410

Enterococci Resistant to Penicillin and Susceptible to Aminoglycosides and Vancomycin...e410

Enterococci Resistant to Penicillin, Aminoglycosides, and Vancomycin...e411

HACEK Microorganisms...e412

Non-HACEK Gram-Negative Bacilli...e413

Enterobacteriaceae...e414

Pseudomonas Species...e414

Unusual Gram-Negative Bacteria...e415

Culture-Negative Endocarditis...e415

Fungi...e416

Endocarditis in IDUs...e418

Etiology of Endocarditis in IDUs...e418

Complications and Their Management...e419

Surgical Therapy...e419

Congestive Heart Failure...e419

Risk of Embolization...e420

Anticoagulation...e421

Periannular Extension of Infection...e421

Splenic Abscess......e422

Mycotic Aneurysms...e422

Intracranial MAs...e422

Extracranial MAs...e423

Outpatient Therapy...e423

Care at Completion of Treatment...e424

Short-Term Follow-Up...e424

Long-Term Follow-Up...e425

Infective endocarditis (IE), like most other syndromes of bacterial infection, has not escaped the impact of burgeoning antibiotic resistance among common pathogens. Since the most recent version of the American Heart Association (AHA) statement addressing treatment of IE was published in 1995,¹ unparalleled changes have occurred in antibiotic susceptibility among the 3 major bacterial causes of IE: streptococci, staphylococci, and enterococci. Reports from different patient populations indicate that multidrug resistance among viridans group streptococci is now characteristic of many colonizing and infecting strains.^2–4 Oxacillin resistance among Staphylococcus aureus (ORSA) isolates is at an all-time high at many tertiary care institutions. In addition, reports^5–7 from several areas of the United States indicate that community-acquired infection resulting from ORSA is frequently seen. Perhaps the most alarming event for S aureus is the development of intermediate- and high-level resistance to vancomycin, which was first described in Japan in 1997⁸ and subsequently reported in several other areas, including the United States.^9–11 Vancomycin resistance among enterococci is characteristic of many of the nosocomial isolates. Increasing aminoglycoside resistance among enterococci has been reported¹² and has potential serious ramifications for treatment efficacy if it becomes more prevalent among enterococcal isolates causing IE.

Coupled with the recent deterioration of antibiotic susceptibility among these groups of Gram-positive cocci is the observation that S aureus has surpassed viridans group streptococci as the leading cause of IE in several recent case series.^13–15 This has resulted in an overall worsening of the average clinical course of patients with endocarditis and has been associated with an increased number of serious complications and higher mortality rates.

The AHA’s recommendations for the treatment of IE have therefore been updated in this statement to better address these microbiological changes. The present Writing Committee conducted a comprehensive review of the literature published between 1990 and 2004 to assist the group in updating the previous version of the guidelines. Literature searches of the PubMed/MEDLINE databases were undertaken to identify pertinent articles. Searches were limited to the English language. The major search terms included endocarditis, infective endocarditis, infectious endocarditis, intracardiac, valvular, mural, infection, diagnosis, bacteremia, case definition, epidemiology, risks, demographics, injection drug use, echocardiography, microbiology, culture-negative, therapy, antibiotic, antifungal, antimicrobial, antimicrobial resistance, adverse drug effects, drug monitoring, outcome, meta-analysis, complications, abscess, congestive heart failure, emboli, stroke, conduction abnormalities, survival, pathogens, organisms, treatment, surgery, indications, valve replacement, valve repair, ambulatory care, trials, and prevention.

In addition, the present statement includes and updates sections of a separate statement¹⁶ that addressed diagnostic and management issues, so that all aspects of endocarditis diagnosis and treatment would be more conveniently presented in a single citation. This work primarily addresses IE in adults; a more detailed review of the unique features of IE in children is available in another statement¹⁷ from the AHA Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease. The Committee has also published a statement¹⁸ on endocarditis that complicates electrophysiological (pacemakers, intracardiac defibrillators), ventricular assist, and other nonvalvular cardiac devices.

	Evidence-Based Scoring System

Top Abstract Introduction Evidence-Based Scoring System Diagnosis Antimicrobial Therapy Staphylococci Enterococci HACEK Microorganisms Enterobacteriaceae Pseudomonas Species Unusual Gram-Negative Bacteria Culture-Negative Endocarditis Fungi Endocarditis in IDUs Etiology of Endocarditis in... Complications and Their... Outpatient Therapy Care at Completion of... References

 
This is the first time that the American College of Cardiology/American Heart Association evidence-based scoring system (see http://circ.ahajournals.org/manual/manual_IIstep6.shtml) has been incorporated into the AHA’s endocarditis treatment guidelines. The purpose of the scoring system is to assist the clinician in interpreting these recommendations and formulating treatment decisions. The system is based on both a classification of recommendations and the level of evidence. Each treatment recommendation has been assigned a class and a level of evidence. The use of this system should support but not supplant the clinician’s decision making in the management of individual patients’ cases.

Classification of Recommendations

Class I: Conditions for which there is evidence, general agreement, or both that a given procedure or treatment is useful and effective.

Class II: Conditions for which there is conflicting evidence, a divergence of opinion, or both about the usefulness/efficacy of a procedure or treatment.
   

   Class IIa: Weight of evidence/opinion is in favor of  usefulness/efficacy.

   Class IIb: Usefulness/efficacy is less well established by evidence/opinion.

Class III: Conditions for which there is evidence, general agreement, or both that the procedure/treatment is not useful/effective and in some cases may be harmful.

Level of Evidence

Level of Evidence A: Data derived from multiple randomized clinical trials

Level of Evidence B: Data derived from a single randomized trial or nonrandomized studies

Level of Evidence C: Consensus opinion of experts

	Diagnosis

Top Abstract Introduction Evidence-Based Scoring System Diagnosis Antimicrobial Therapy Staphylococci Enterococci HACEK Microorganisms Enterobacteriaceae Pseudomonas Species Unusual Gram-Negative Bacteria Culture-Negative Endocarditis Fungi Endocarditis in IDUs Etiology of Endocarditis in... Complications and Their... Outpatient Therapy Care at Completion of... References

 
The diagnosis of IE is straightforward in patients with classic Oslerian manifestations: bacteremia or fungemia, evidence of active valvulitis, peripheral emboli, and immunologic vascular phenomena. In other patients, however, the classic peripheral stigmata may be few or absent. This may occur during acute courses of IE, particularly among patients who are injection drug users (IDUs), in whom IE is often the result of S aureus infection of right-sided heart valves. Acute IE may evolve too quickly for the development of immunologic vascular phenomena, which are more characteristic of subacute IE. In addition, valve lesions in acute right-sided IE usually do not create the peripheral emboli and immunologic vascular phenomena that can result from left-sided valvular involvement. Right-sided IE can cause septic pulmonary emboli, however.

The variability in clinical presentation of IE requires a diagnostic strategy that is both sensitive for disease detection and specific for its exclusion across all forms of the disease. In 1994, Durack and colleagues¹⁹ from Duke University Medical Center proposed a diagnostic schema termed the Duke criteria, which stratified patients with suspected IE into 3 categories: "definite" cases, identified either clinically or pathologically (IE proved at surgery or autopsy); "possible" cases (not meeting the criteria for definite IE); and "rejected" cases (no pathological evidence of IE at autopsy or surgery, rapid resolution of the clinical syndrome with either no treatment or short-term antibiotic therapy, or a firm alternative diagnosis).

A diagnosis of IE is based on the presence of either major or minor clinical criteria. Major criteria in the Duke strategy included IE documented by data obtained at the time of open heart surgery or autopsy (pathologically definite) or by well-defined microbiological criteria (high-grade bacteremia or fungemia) plus echocardiographic data (clinically definite). To maintain the high specificity of blood culture results for IE, the Duke criteria required that some patients with high-grade bacteremia with common IE pathogens also fulfill secondary criteria. For example, bacteremia resulting from viridans streptococci and members of the HACEK group of fastidious Gram-negative rods, which are classic IE pathogens but uncommonly seen in patients without IE, are given primary diagnostic weight. In contrast, S aureus and Enterococcus faecalis commonly cause both IE and non-IE bacteremias. The Duke criteria therefore gave diagnostic weight to bacteremia with staphylococci or enterococci only when they were community acquired and without an apparent primary focus; these latter types of bacteremia have the highest risk of being associated with IE.^19,20

The Duke criteria incorporated echocardiographic findings in the diagnostic strategy. Major diagnostic weight was given to only 3 typical echocardiographic findings: mobile, echodense masses attached to valvular leaflets or mural endocardium; periannular abscesses; or new dehiscence of a valvular prosthesis (see Echocardiography).

Six common but less specific findings of IE also were included as minor criteria in the original Duke schema: intermittent bacteremia or fungemia, fever, major embolic events, nonembolic vascular phenomena, underlying valvular disease or injection drug use, and echocardiographic abnormalities that fell short of typical valvular vegetations, abscesses, or dehiscence. Clinically definite IE by the Duke criteria required the presence of 2 major criteria, 1 major criterion and 3 minor criteria, or 5 minor criteria. In the mid- to late 1990s, direct analyses of the Duke criteria were made in 11 major studies,^21–32 including nearly 1700 patients composed of geographically and clinically diverse groups (adult, pediatric, older adult [>60 years old], patients from the community, patients with and without injection drug use, and patients with both native and prosthetic valves). These studies^21–32 confirmed the high sensitivity and specificity of the Duke criteria and the diagnostic utility of echocardiography in identifying clinically definite cases. Moreover, a retrospective study of 410 patients showed good agreement (72% to 90%) between the Duke criteria and clinical assessment by infectious disease experts blinded to underlying IE risk factors.³³

Several refinements have been made recently to both the major and minor Duke criteria. As noted above, in the original Duke criteria, bacteremia resulting from S aureus was considered to fulfill a major criterion only if it was community acquired because ample literature has suggested that this parameter is an important surrogate marker for underlying IE.²⁰ An increasing number of contemporary studies, however, have documented IE in patients experiencing nosocomial staphylococcal bacteremia. For example, of 59 consecutive patients with S aureus IE, 45.8% had nosocomially acquired infections and 50.8% had a removable focus of infection.³⁴ In a more recent analysis of 262 patients at Duke University Medical Center who had hospital-acquired S aureus bacteremia, 34 (13%) were subsequently diagnosed with definite IE. Therefore, the modified Duke criteria (Tables 1A and 1B) recommend the inclusion of S aureus bacteremia as a major criterion, regardless of whether the infection is nosocomially acquired (with or without a removable source of infection) or community acquired.³⁵

View this table: [in this window] [in a new window]   TABLE 1A. Definition of Infective Endocarditis According to the Modified Duke Criteria

View this table: [in this window] [in a new window]   TABLE 1B. Definition of Terms Used in the Modified Duke Criteria for the Diagnosis of Infective Endocarditis

Specific serological data have now been included to more precisely establish the etiologic agents of "culture-negative" endocarditis (as a surrogate for positive blood cultures). Such serological criteria would be applied in circumstances in which the etiologic organism is slow growing or requires special culture media (eg, Brucella) or in which the organism is not readily cultivated in most clinical microbiology laboratories (eg, Coxiella burnetii). For example, in the original Duke criteria, a positive serology for Q fever was considered a minor microbiological criterion. Subsequently, Fournier et al³⁶ studied 20 pathologically confirmed cases of Q fever IE. When the original Duke criteria were used, 4 of the 20 patients were classified as having "possible IE." When Q fever serological results and a single blood culture positive for C burnetii were considered to be a major criterion, however, each of these 4 cases was reclassified from possible IE to "definite IE." On the basis of these data, specific serological data as a surrogate marker for positive blood cultures have now been included. An anti–phase I immunoglobulin G antibody titer 1:800 or a single blood culture positive for C burnetii should be major criteria in the modified Duke schema.

Serological tests and polymerase chain reaction (PCR)–based testing for other difficult-to-cultivate organisms, such as Bartonella quintana or Tropheryma whippelii, also have been discussed as future major criteria. At present, there are significant methodological problems and uncertainties for proposing antibody titers that are positive for Bartonella and Chlamydia species or for PCR-based testing for T whippelii as major criteria in the Duke schema. For example, endocarditis infections caused by Bartonella and Chlamydia species often are indistinguishable in serological test results because of cross-reactions.³⁷ PCR-based tests have low sensitivity unless the tests are performed directly on cardiac valvular tissue.^38–40 Moreover, few centers provide timely PCR-based testing for these rare causes of IE. Therefore, the inclusion of such assays as major criteria should be deferred until the serodiagnostic and PCR approaches can be standardized and validated in a sufficient number of cases of these rare types of IE, the aforementioned technical problems are resolved, and the availability of such assays becomes more widespread.

The expansion of minor criteria to include elevated erythrocyte sedimentation rate or C-reactive protein, the presence of newly diagnosed clubbing, splenomegaly, and microscopic hematuria also has been proposed. In a study of 100 consecutive cases of pathologically proven native valve IE, inclusion of these additional parameters with the existing Duke minor criteria resulted in a 10% increase in the frequency of cases being deemed clinically definite, with no loss of specificity. These additional parameters have not been formally integrated into the modified Duke criteria, however.⁴¹

One minor criterion from the original Duke schema, "echocardiogram consistent with IE but not meeting major criterion," has been reevaluated. This criterion originally was used in cases in which nonspecific valvular thickening was detected by transthoracic echocardiography (TTE). In a reanalysis of patients in the Duke University database (containing records collected prospectively on >800 cases of definite and possible IE since 1984), this echocardiographic criterion was used in only 5% of cases and was never used in the final analysis of any patient who underwent transesophageal echocardiography (TEE). Therefore, this minor criterion was eliminated in the modified Duke criteria.

Finally, adjustment of the Duke criteria to require a minimum of 1 major and 1 minor criterion or 3 minor criteria as a "floor" to designate a case as possible IE (as opposed to "findings consistent with IE that fall short of ‘definite’ but not ‘rejected’") has been incorporated into the modified criteria to reduce the proportion of patients assigned to that category. This approach was used in a series of patients initially categorized as possible IE by the original Duke criteria. With the guidance of the "diagnostic floor," a number of these cases were reclassified as "rejected" for IE.³⁵ Follow-up in these reclassified patients documented the specificity of this diagnostic schema because no patients developed IE during the subsequent 12 weeks.

Thus, on the basis of the weight of clinical evidence involving nearly 2000 patients in the current literature, it appears that patients suspected of having IE should be clinically evaluated, with the modified Duke criteria as the primary diagnostic schema. It should be pointed out that the Duke criteria were primarily developed to facilitate epidemiological and clinical research efforts so that investigators could compare and contrast the clinical features and outcomes of various case series of patients. Extending these criteria to the clinical practice setting has been somewhat more difficult. Because IE is a heterogeneous disease with highly variable clinical presentations, the use of criteria alone will never suffice. Criteria changes that add sensitivity often do so at the expense of specificity and vice versa. The Duke criteria are meant to be a clinical guide for diagnosing IE and must not replace clinical judgment. Clinicians may appropriately and wisely decide whether to treat or not treat an individual patient, regardless of whether they meet or fail to meet the criteria for definite or possible IE by the Duke schema. We believe, however, that the modifications of the Duke criteria (Tables 1A and 1B) will help investigators who wish to examine the clinical and epidemiological features of IE and will serve as a guide for clinicians struggling with difficult diagnostic problems. These modifications require further validation among patients who are hospitalized in both community-based and tertiary care hospitals, with particular attention to longer-term follow-up of patients rejected as having IE because they did not meet the minimal floor criteria for possible IE.

The diagnosis of endocarditis must be made as soon as possible to initiate therapy and identify patients at high risk for complications who may be best managed by early surgery. In cases with a high suspicion of endocarditis, based on either the clinical picture or the patient’s risk factor profile, such as injection drug use or a history of previous endocarditis, the presumption of endocarditis often is made before blood culture results are available. Identification of vegetations and incremental valvular insufficiency with echocardiography often completes the diagnostic criteria for IE and affects duration of therapy. Although the use of case definitions to establish a diagnosis of IE should not replace clinical judgment,⁴² the recently modified Duke criteria³⁵ have been useful in both epidemiological and clinical trials and in individual patient management. Clinical, echocardiographic, and microbiological criteria (Tables 1A and 1B) are used routinely to support a diagnosis of IE, and they do not rely on histopathologic confirmation of resected valvular material or arterial embolus. If suggestive features are absent, then a negative echocardiogram may prompt a more thorough search for alternative sources of fever and sepsis. In light of these important functions, echocardiography should be performed urgently in patients suspected of having endocarditis.

Echocardiography
Echocardiography is central to the diagnosis and management of patients with IE. As previously stated, echocardiographic evidence of an oscillating intracardiac mass or vegetation, an annular abscess, prosthetic valve partial dehiscence, and new valvular regurgitation are major criteria in the diagnosis of IE.

Echocardiography should be performed in all cases of suspected IE (Class I, Level of Evidence: A). Whether TTE or TEE should be performed first depends on the clinical scenario (Figure). If the clinical suspicion is relatively low or imaging is likely to be of good quality (many children), then it is reasonable to perform TTE. When imaging is difficult or poor, TEE should be considered. If any circumstances preclude securing optimal echocardiographic windows, including chronic obstructive lung disease, previous thoracic surgery, morbid obesity, or other conditions, then TEE should be performed instead of TTE. If TTE is negative and clinical suspicion remains low, then other clinical entities should be considered. If TTE shows vegetations but the likelihood of complications is low, then subsequent TEE is unlikely to alter initial medical management. On the other hand, if clinical suspicion of IE or its complications is high (prosthetic valve, staphylococcal bacteremia, or new atrioventricular block), then negative TTE will not definitely rule out IE or its potential complications, and TEE should be performed first. Investigation in adults has shown TEE to be more sensitive than TTE for the detection of vegetations and abscesses.⁴³ In addition, in the setting of a prosthetic valve, transthoracic images are greatly hampered by the structural components of the prosthesis and are inadequate for assessment of the perivalvar area where those infections often start.⁴⁴ Although cost-effectiveness calculations suggest that TEE should be the first examination in adults with suspected IE (Table 2), particularly in the setting of staphylococcal bacteremia,^45,46 many patients are not candidates for immediate TEE because of oral intake during the preceding 6 hours or because the patients are in institutions that cannot provide 24-hour TEE services. When TEE is not clinically possible or must be delayed, early TTE should be performed without delay. Although TTE will not definitively exclude vegetations or abscesses, it will allow identification of very high-risk patients, establish the diagnosis in many, and guide early treatment decisions.

View larger version (26K): [in this window] [in a new window]   An approach to the diagnostic use of echocardiography (echo). *High-risk echocardiographic features include large and/or mobile vegetations, valvular insufficiency, suggestion of perivalvular extension, or secondary ventricular dysfunction (see text). For example, a patient with fever and a previously known heart murmur and no other stigmata of IE. +High initial patient risks include prosthetic heart valves, many congenital heart diseases, previous endocarditis, new murmur, heart failure, or other stigmata of endocarditis. Rx indicates antibiotic treatment for endocarditis. Reproduced with permission from: Bayer AS, Bolger AF, Taubert KA, Wilson W, Steckelberg J, Karchmer AW, Levison M, Chambers HF, Dajani AS, Gewitz MH, Newburger JW, Gerber MA, Shulman ST, Pallasch TJ, Gage TW, Ferrieri P. Diagnosis and Management of Infective Endocarditis and Its Complications. Circulation. 1998;98:2936–2948.

View this table: [in this window] [in a new window]   TABLE 2. Use of Echocardiography During Diagnosis and Treatment of Endocarditis

Many findings identified by TEE also can be detected on transthoracic views. Concurrent TTE images can serve as a baseline for rapid and noninvasive comparison of vegetation size, valvular insufficiency, or change in abscess cavities during the course of the patient’s treatment should clinical deterioration occur. Some findings, such as tricuspid vegetations or abnormalities of the right ventricular outflow tract, may occasionally be better visualized with TTE than with TEE.⁴⁷

Both TEE and TTE may produce false-negative results if vegetations are small or have already embolized.⁴⁸ Even TEE may miss initial perivalvular abscesses, particularly when the study is performed early in the patient’s illness.⁴⁹ In such cases, the incipient abscess may be seen only as nonspecific perivalvular thickening, which on repeat imaging across several days may become recognizable as it expands and cavitates. Similarly, perivalvular fistulae and pseudoaneurysms develop over time, and negative early TEE images do not exclude the potential for their development.

False-positive results from TEE or TTE studies may occur when valvular abnormalities are seen that may not be related to a current infection. Previous scarring, severe myxomatous change, and even normal structures such as Lambl’s excrescences may be indistinguishable from active changes on the valves. As echocardiographic technology improves, with higher frequencies and refined beam-forming technology, more subtle findings continue to be recognized and may add to the category of indeterminate findings. One approach to minimizing confusion from these structures is to exploit the high frame rates that are often available with current equipment to improve temporal resolution and clearly visualize rapidly moving structures such as microcavitations from prosthetic valves or fibrillar components.

Several echocardiographic features identify patients at high risk for a complicated course or with a need for surgery (Table 3). These features include large vegetations, severe valvular insufficiency, abscess cavities or pseudoaneurysms, valvular perforation or dehiscence, and evidence of decompensated heart failure.¹⁶ The ability of echocardiographic features to predict embolic events is limited.^50–52 The greatest risk appears to occur with large vegetations (>10 mm in diameter) on the anterior mitral leaflet.⁵³ Vegetation size and mobility must be taken into account, along with bacteriologic factors and other indications for surgery, when considering early surgery to avoid embolization.⁵⁴

View this table: [in this window] [in a new window]   TABLE 3. Echocardiographic Features That Suggest Potential Need for Surgical Intervention

Repeat Echocardiography
If the initial TTE images are negative and the diagnosis of IE is still being considered, then TEE should be performed as soon as possible (Table 2; Class I, Level of Evidence: A). Among patients with an initial positive TTE and a high risk for cardiac complications including perivalvular extension of infection, TEE should be obtained as soon as possible (Class I, Level of Evidence: A). Repeating TEE 7 to 10 days after an initial "negative" result is often advisable (Class I, Level of Evidence: B) when clinical suspicion of IE persists.⁵⁵ In some cases, vegetations may reach detectable size in the interval, or abscess cavities or fistulous tracts may become clear. An interval increase in vegetation size on serial echocardiography despite the administration of appropriate antibiotic therapy has serious implications and has been associated with an increased risk of complications and the need for surgery.⁵⁵ Repeat TEE also may be useful when a patient with an initially positive TEE develops worrisome clinical features during antibiotic therapy (Class I, Level of Evidence: A). Unexplained progression of heart failure symptoms, change in cardiac murmurs, and new atrioventricular block or arrhythmia should prompt emergent evaluation by TEE if possible or by TTE if necessary to minimize delay.

Intraoperative Echocardiography
Preoperative surgical planning for patients with IE will benefit from echocardiographic delineation of the mechanisms of valvular dysfunction or regions of myocardial disruption (Table 3). The use of aortic homografts is facilitated by preoperative estimates of annular size, which allow the selection of appropriately sized donor tissues.^56,57 Intraoperatively, echocardiographic goals include assessment of not only the obviously dysfunctional valve but also the other valves and contiguous structures. Post–cardiopulmonary bypass images should confirm the adequacy of the repair or replacement and document the successful closure of fistulous tracts. Perivalvular leaks related to technical factors should be recognized and documented to avoid later confusion about whether the leaks are the result of recurrent infection. During postpump imaging, it is often necessary to augment afterload to reach representative ambulatory levels to avoid underestimation of regurgitant jet size and significance and to ensure that abnormal communications have been closed.⁵⁸ Afterload augmentation, however, may not mimic actual awake physiology and may still lead occasionally to an inaccurate evaluation of the awake postoperative state.

Echocardiography at Completion of Therapy
All patients who have experienced an episode of endocarditis remain at high risk for recurrent infection indefinitely. It is extremely important for the future care of these patients to establish a new baseline for valvular morphology, including the presence of vegetations, ventricular function, and valvular insufficiency once treatment has been completed. Documentation of heart rate, heart rhythm, and blood pressure at the time of echocardiographic study is important because changes in these conditions may explain future differences in valvular insufficiency independent of pathology (Table 2). TTE is preferable (Class IIb, Level of Evidence: C) for this because measurements of vegetation size are more reproducible and spectral Doppler interrogation often is more thorough than TEE. TEE, however, may be merited to define the new baseline in some patients with poor acoustic windows or complicated anatomy, such as after extensive debridement and reconstruction. Although intraoperative postpump TEE views may be adequate for this new baseline, they should be reviewed for adequacy and repeated if necessary. Some patients will have valvular dysfunction at the end of otherwise successful treatment; clearly, they will require eventual surgery. Posttreatment echocardiography can guide both medical management and the discussion of the appropriate timing of the intervention.

	Antimicrobial Therapy

Top Abstract Introduction Evidence-Based Scoring System Diagnosis Antimicrobial Therapy Staphylococci Enterococci HACEK Microorganisms Enterobacteriaceae Pseudomonas Species Unusual Gram-Negative Bacteria Culture-Negative Endocarditis Fungi Endocarditis in IDUs Etiology of Endocarditis in... Complications and Their... Outpatient Therapy Care at Completion of... References

 
Antimicrobial Treatment Perspectives
Results of clinical efficacy studies support the use of most treatment regimens described in these guidelines (Class I, Level of Evidence: A). Other recommendations (Class IIa, Level of Evidence: C) listed herein are based largely on in vitro data and consensus opinion and include the following 3 criteria. First, the counting of days of recommended duration of therapy should begin on the first day on which blood cultures were negative in cases in which blood cultures were initially positive. At least 2 sets of blood cultures should be obtained every 24 to 48 hours until bloodstream infection is cleared. Second, for patients with native valve endocarditis who undergo valve resection with prosthetic valve replacement, the postoperative treatment regimen should be one that is recommended for prosthetic valve treatment rather than one that is recommended for native valve treatment. If the resected tissue is culture positive, then an entire course of antimicrobial therapy is recommended after valve resection. If the resected tissue is culture negative, then the recommended duration of prosthetic valve treatment should be given less the number of days of treatment administered for native valve infection before valve replacement. Third, in regimens that contain combination antimicrobial therapy, it is important to administer agents at the same time or temporally close together to maximize the synergistic killing effect on an infecting pathogen.

Overview of Viridans Group Streptococci, Streptococcus bovis, Abiotrophia defectiva, Granulicatella Species, and Gemella Species
Viridans group streptococci, or -hemolytic streptococci, are common etiologic agents that are the cause of community-acquired native valve endocarditis in patients who are not intravenous drug users (IDUs). The taxonomy of viridans group streptococci is evolving. The species that most commonly cause endocarditis are S sanguis, S oralis (mitis), S salivarius, S mutans, and Gemella morbillorum (formerly called S morbillorum). Members of the S anginosus group (S intermedius, anginosus, and constellatus) also have been referred to as the S milleri group, and this has caused some confusion. In contrast to other -hemolytic streptococcal species, the S anginosus group tends to form abscesses and cause hematogenously disseminated infection (eg, myocardial and visceral abscesses, septic arthritis, vertebral osteomyelitis). Consequently, the duration of antimicrobial treatment of endocarditis caused by these organisms may need to be longer than that for endocarditis caused by other -hemolytic streptococci. In addition, although the S intermedius group usually is sensitive to penicillin, some strains may exhibit variable penicillin resistance. Species of Gemella (morbillorum, bergeriae, sanguinis, and hemolysans) share some physiological characteristics with nutritionally variant streptococci, and endocarditis caused by these organisms should be treated with more aggressive combination therapy such as that used for nutritionally variant streptococcal endocarditis (see below). The recommendations that follow are intended to assist clinicians in selecting appropriate antimicrobial therapy for patients with endocarditis caused by viridans group streptococci and S bovis (a nonenterococcal penicillin-susceptible group D streptococcus). S bovis expresses the group D antigen, but it can be distinguished from group D Enterococcus by appropriate biochemical tests. Patients with either S bovis bacteremia or endocarditis should undergo colonoscopy to determine whether malignancy or other mucosal lesions are present.

Certain viridans group streptococci have biological characteristics that may complicate diagnosis and therapy. Some strains, such as the newly named Abiotrophia defectiva and Granulicatella species (G elegans, G adiacens, G paraadiacens, and G balaenopterae; formerly known as nutritionally variant streptococci), have nutritional deficiencies that hinder their growth in routine laboratory culture media. Such organisms may require broth supplemented with pyridoxal hydrochloride or cysteine. In addition, some strains of viridans group streptococci may exhibit a laboratory phenomenon called "penicillin tolerance." For tolerant strains, the minimum bactericidal concentration (MBC) of penicillin greatly exceeds the minimum inhibitory concentration (MIC) (usually by >32-fold). These strains are killed more slowly by penicillin in animal models of endocarditis.⁵⁹ There are no published data on the influence of tolerance on the outcome of endocarditis in humans, however, and we believe that laboratory demonstration of tolerance has no implication for the selection of antimicrobial therapy for endocarditis resulting from viridans group streptococci. Accordingly, the determination of MBC for these microorganisms is not routinely recommended (Class IIa, Level of Evidence: C).

It should be noted that treatment regimens outlined for viridans group streptococci, S bovis, A defectiva, Granulicatella species, and Gemella species are subdivided into categories based on penicillin MIC data. These subdivisions are not based on Clinical and Laboratory Standards Institute (CLIS, formally known as the National Committee for Clinical Laboratory Standards, or NCCLS) recommended break points that are used to define penicillin susceptibility.

Highly Penicillin-Susceptible Viridans Group Streptococci and S bovis (MIC 0.12 µg/mL)
Bacteriologic cure rates 98% may be anticipated in patients who complete 4 weeks of therapy with parenteral penicillin or ceftriaxone for endocarditis caused by highly penicillin-susceptible viridans group streptococci or S bovis.^60,61 Ampicillin is an alternative to penicillin and has been used when penicillin is not available because of supply deficiencies. The addition of gentamicin sulfate to penicillin exerts a synergistic killing effect in vitro on viridans group streptococci and S bovis. The combination of penicillin or ceftriaxone together with gentamicin results in synergistic killing in vivo in animal models of viridans group streptococcal or S bovis experimental endocarditis.

In selected patients, treatment with a 2-week regimen with either penicillin or ceftriaxone combined with an aminoglycoside resulted in cure rates that are similar to those after monotherapy with penicillin or ceftriaxone administered for 4 weeks.^61,62 Studies performed in Europe, South America, and the United States demonstrated that the combination of once-daily ceftriaxone with either netilmicin or gentamicin administered once daily was equivalent in efficacy to 2 weeks of therapy with penicillin together with an aminoglycoside administered in daily divided doses.^62,63 The 2-week regimen of penicillin or ceftriaxone combined with single daily-dose gentamicin is appropriate for uncomplicated cases of endocarditis caused by highly penicillin-susceptible viridans group streptococci or S bovis in patients at low risk for adverse events caused by gentamicin therapy (Table 4). This 2-week regimen is not recommended for patients with known extracardiac infection or those with a creatinine clearance of <20 mL/min.

View this table: [in this window] [in a new window]   TABLE 4. Therapy of Native Valve Endocarditis Caused by Highly Penicillin-Susceptible Viridans Group Streptococci and Streptococcus bovis

Although the two 4-week ß-lactam–containing regimens shown in Table 4 produce similar outcomes, each regimen has advantages and disadvantages. Monotherapy with either penicillin or ceftriaxone for 4 weeks avoids the use of gentamicin, which is potentially ototoxic and nephrotoxic. Compared with penicillin, the advantage of once-daily ceftriaxone is its simplicity for use in therapy administered to outpatients.^60,64

For patients who are unable to tolerate penicillin or ceftriaxone, vancomycin is the most effective alternative. Prolonged intravenous use of vancomycin may be complicated by thrombophlebitis, rash, fever, anemia, thrombocytopenia, and, rarely, ototoxic reactions. Vancomycin should be infused for 1 hour to reduce the risk of the histamine release–associated "red man" syndrome.

Viridans Group Streptococci and S bovis With Penicillin MIC >0.12 to 0.5 µg/mL
Penicillin resistance in vitro is increasing in frequency among strains of viridans group streptococci and S bovis. Table 5 shows regimens recommended for native valve endocarditis caused by relatively penicillin-resistant strains (MIC >0.12 to 0.5 µg/mL). For patients with viridans group streptococcal or S bovis endocarditis, penicillin or ceftriaxone should be administered for 4 weeks together with single daily-dose gentamicin for the first 2 weeks of treatment.

View this table: [in this window] [in a new window]   TABLE 5. Therapy of Native Valve Endocarditis Caused by Strains of Viridans Group Streptococci and Streptococcus bovis Relatively Resistant to Penicillin

Abiotrophia defectiva and Granulicatella Species, Gemella Species, and Viridans Group Streptococci With Penicillin MIC >0.5 µg/mL
The determination of antimicrobial susceptibilities of A defectiva, Granulicatella species (formerly known as nutritionally variant streptococci), and Gemella species is often technically difficult, and the results may not be accurate. Moreover, endocarditis caused by these microorganisms has been more difficult to cure microbiologically than has endocarditis caused by a strain of non-nutritionally variant group viridans streptococci.⁶⁵ For these reasons, patients with endocarditis caused by A defectiva, Granulicatella species, and Gemella species should be treated with a regimen that is recommended for enterococcal endocarditis (Table 9). Patients with endocarditis caused by a microorganism with an MIC to penicillin >0.5 µg/mL should be treated with a regimen recommended for enterococcal endocarditis (Table 9). When vancomycin is the chosen antibiotic, the addition of gentamicin is not necessary.

Endocarditis of Prosthetic Valves or Other Prosthetic Material Caused by Viridans Group Streptococci and S bovis
Patients with endocarditis complicating prosthetic valves or other prosthetic material caused by a highly penicillin-susceptible strain (MIC 0.12 µg/mL) should receive 6 weeks of therapy with penicillin or ceftriaxone with or without gentamicin for the first 2 weeks (Table 6). Endocarditis caused by a strain that is relatively or highly resistant to penicillin (MIC >0.12 µg/mL) should receive 6 weeks of therapy with a combination of penicillin or ceftriaxone together with gentamicin. Vancomycin therapy is recommended only for patients who are unable to tolerate penicillin or ceftriaxone.

View this table: [in this window] [in a new window]   TABLE 6. Therapy for Endocarditis of Prosthetic Valves or Other Prosthetic Material Caused by Viridans Group Streptococci and Streptococcus bovis

S pneumoniae, S pyogenes, and Groups B, C, and G Streptococci
Endocarditis caused by these streptococci is relatively uncommon. There are few published reports of large series of cases evaluating therapeutic regimens for endocarditis caused by these microorganisms. When S pneumoniae is recovered from a patient with endocarditis, the organism should be tested for penicillin susceptibility. Patients with endocarditis caused by highly penicillin-susceptible S pneumoniae should receive 4 weeks of antimicrobial therapy with penicillin, cefazolin, or ceftriaxone. Vancomycin should be administered only to patients who are unable to tolerate ß-lactam therapy. Increasingly, S pneumoniae with intermediate penicillin resistance (MIC >0.1 to 1.0 µg/mL) or high penicillin resistance (MIC 2.0 µg/mL) is being recovered from patients with bacteremia.⁶⁶ Moreover, cross-resistance of pneumococci to other antimicrobial agents, such as cephalosporins, macrolides, fluoroquinolones, carbapenems, and even vancomycin, is increasing in frequency. In one multicenter study⁶⁷ with a relatively large (n=24) number of patients with IE caused by S pneumoniae resistant to penicillin (MIC 0.1 to 4 µg/mL), patients were evaluated and compared with 39 patients who were infected with penicillin-susceptible strains. Several observations were made. Infection by penicillin-resistant strains did not worsen prognosis. High-dose penicillin or a third-generation cephalosporin can be used in patients with penicillin-resistant infection and without meningitis. In patients with IE and meningitis, high doses of cefotaxime may be used. If the isolate is resistant (MIC 2 µg/mL) to cefotaxime, then the addition of vancomycin and rifampin should be considered. Of course, these findings are based on current levels of resistance, and increasing MICs could dictate revisions in future treatment selections. Accordingly, the treatment of patients with pneumococcal endocarditis should be coordinated in consultation with an infectious diseases specialist.

Results of logistic regression analysis of clinical variables from cases of pneumococcal endocarditis demonstrate the potential value of valve replacement in preventing early death. The increased number of patients undergoing valve replacement surgery surveyed in a multicenter study from France⁶⁸ may account in part for the improved outcome in recent years.

Aqueous crystalline penicillin G administered intravenously (IV) for 4 weeks is the recommended treatment, based on limited published data for the treatment of endocarditis caused by S pyogenes. Cefazolin or ceftriaxone is an acceptable alternative to penicillin. Vancomycin therapy should be administered only to patients who are unable to tolerate a ß-lactam antibiotic. In general, strains of group B, C, and G streptococci are slightly more resistant to penicillin than are strains of group A streptococci. Some authorities recommend the addition of gentamicin to penicillin or a cephalosporin for at least the first 2 weeks of a 4- to 6-week course of antimicrobial therapy for group B, C, and G streptococcal IE.^69,70 There is a clinical impression^71,72 that early cardiac surgery intervention has improved overall survival rates among more recently treated patients with ß-hemolytic streptococcal endocarditis as compared with patients treated decades ago. Because of the relative infrequency of endocarditis caused by these microorganisms, consultation with an infectious diseases specialist for the treatment of these patients is recommended.

	Staphylococci

Top Abstract Introduction Evidence-Based Scoring System Diagnosis Antimicrobial Therapy Staphylococci Enterococci HACEK Microorganisms Enterobacteriaceae Pseudomonas Species Unusual Gram-Negative Bacteria Culture-Negative Endocarditis Fungi Endocarditis in IDUs Etiology of Endocarditis in... Complications and Their... Outpatient Therapy Care at Completion of... References

 
IE may be caused by staphylococci that are coagulase positive (S aureus) or coagulase negative (S epidermidis and various other species). Traditionally, it has been believed that coagulase-positive staphylococci cause primarily native valve endocarditis, whereas coagulase-negative staphylococci (CoNS) are thought to cause primarily prosthetic valve endocarditis, but considerable overlap exists. For example, in a recent multicenter, prospective, observational investigation involving >1000 consecutive patients with definite IE from >20 countries, S aureus was the most common cause of prosthetic valve IE (25.8% of 214 cases), whereas 64 (8%) cases of native valve endocarditis resulted from CoNS.⁷³ Thus, it is important to consider both pathogens when a patient with suspected endocarditis has a preliminary blood culture that suggests staphylococci by Gram’s stain interpretation.

S aureus
S aureus is the most common cause of IE in much of the developed world.⁷⁴ This increase is primarily a consequence of healthcare contact (eg, intravascular catheters, surgical wounds, indwelling prosthetic devices).^73–76 Increasing rates of oxacillin resistance in both hospital and community settings and the recovery of clinical S aureus isolates both partially⁷⁷ and fully⁷⁸ resistant to vancomycin have complicated the treatment of S aureus endocarditis. In nonaddicts, endocarditis arising from S aureus primarily involves the left side of the heart and is associated with mortality rates ranging from 25% to 40%. S aureus endocarditis in IDUs often involves the tricuspid valve. Cure rates for right-sided S aureus endocarditis in IDUs are high (>85%) and may be achieved with relatively short courses of treatment (<4 weeks; see below).

Coagulase-Negative Staphylococci
Although CoNS are one of the most common causes of prosthetic valve endocarditis,⁷⁹ the role of CoNS as pathogens on native valves is well documented.^80–82 Most of the patients with native valve endocarditis had documented underlying valvular abnormalities, particularly mitral valve prolapse. Their clinical course is typically indolent with a satisfactory response to medical or surgical therapy.

An important subset of patients with CoNS IE has been identified recently: those with infection caused by S lugdunensis. This species of CoNS tends to cause a substantially more virulent form of IE, with a high rate of perivalvular extension of infection and metastatic infection. This organism is uniformly susceptible in vitro to most antibiotics.^83–89 Most experts recommend that endocarditis caused by this organism be treated with standard regimens based on the in vitro susceptibility profiles of the strain. The patient also should be monitored carefully for the development of periannular extension or extracardiac spread of infection. The microbiological differentiation of S lugdunensis from other CoNS may be difficult,⁸⁹ and many laboratories do not have the capability to assign species identification to CoNS isolates.

Endocarditis Caused by Staphylococci in the Absence of Prosthetic Valves
Right-Sided Endocarditis in IDUs
The addition of gentamicin to nafcillin accelerates the killing of methicillin-susceptible staphylococci in vitro. In experimentally induced cardiac vegetations, the data support the use of combined gentamicin-nafcillin therapy in humans with right-sided IE. For example, in IDUs with uncomplicated right-sided S aureus endocarditis (no evidence of renal failure, extrapulmonary metastatic infections, aortic or mitral valve involvement, meningitis, or infection by oxacillin-resistant S aureus, or ORSA), combined ß-lactam-aminoglycoside short-course (2 weeks) therapy was effective in several studies.^90–94 In one study,⁹² such combination therapy had excellent efficacy in HIV-infected patients (most with CD4 counts >300 x10⁶ cells) and in those who had large tricuspid valve vegetations (>10 mm in diameter). A more recent study showed that a 2-week monotherapy regimen of cloxacillin was equivalent to that of cloxacillin plus gentamicin administered for 2 weeks.⁹³ By contrast, glycopeptide (teicoplanin or vancomycin) plus gentamicin-based short-course regimens appeared to be less effective for right-sided S aureus IE caused by either oxacillin-susceptible S aureus (OSSA) or ORSA strains.⁹² These glycopeptides may be less effective because of limited bactericidal activity, poor penetration into vegetations, and increased drug clearance among IDUs.⁹⁵ Thus, the weight of evidence suggests that parenteral ß-lactam short-course therapy, with or without aminoglycoside, is adequate for the treatment of uncomplicated OSSA right-sided IE. In contrast, glycopeptide therapy (with or without adjunctive gentamicin) often requires more prolonged treatment regimens.

In patients who will not comply with a course of parenteral antibiotic therapy, oral treatment may be an option. Two studies have evaluated the use of predominantly oral 4-week antibiotic regimens (ciprofloxacin plus rifampin) for the therapy of uncomplicated right-sided S aureus endocarditis in IDUs.^96,97 In each study, including one in which >70% of patients were HIV-seropositive,⁹⁷ cure rates were >90%.

Endocarditis in Non-IDUs
Anecdotal case reports in nonaddicts with staphylococcal endocarditis suggest that the use of gentamicin-nafcillin therapy may be of benefit in patients who fail to respond to monotherapy with nafcillin.⁹⁸ This issue was addressed in a multicenter prospective trial comparing nafcillin alone for 6 weeks with nafcillin plus gentamicin (for the initial 2 weeks) in the treatment of predominantly left-sided endocarditis caused by S aureus.⁹⁹ Nafcillin-gentamicin therapy reduced the duration of bacteremia by 1 day as compared with nafcillin monotherapy. The combination therapy did not reduce mortality or the frequency of cardiac complications, however, but it did result in an increased frequency of gentamicin-associated nephrotoxicity. Many authorities thus recommend the use of combination therapy for the first 3 to 5 days of therapy for left-sided S aureus endocarditis, especially in fulminant cases (Table 7). Experience to date with gentamicin in the treatment of left-sided native valve S aureus endocarditis has involved multiple daily-dosing schedules. Thus, pending further clinical data, when gentamicin is used for this indication, it should be administered whenever possible in a 2- or 3-times-daily dosing schedule, with a total daily gentamicin dose not to exceed 3 mg/kg in patients with normal renal function. Gentamicin therapy should be discontinued after the first 3 to 5 days of therapy.

View this table: [in this window] [in a new window]   TABLE 7. Therapy for Endocarditis Caused by Staphylococci in the Absence of Prosthetic Materials

Thus, in summary, for both right- and left-sided S aureus endocarditis, there is little compelling evidence that adjunctive gentamicin therapy, especially beyond 3 to 5 days, confers additional clinical benefit¹⁰⁰ and is optional. Rarely, staphylococci are susceptible to penicillin and do not produce ß-lactamase; these patients may be treated with penicillin.

There are no evidence-based data that demonstrate the most appropriate duration of nafcillin therapy for treatment of left-sided native valve IE caused by OSSA. For patients with uncomplicated infection, ^</