Negative blood cultures in infective endocarditis: a review

Molecular detection of Coxiella burnetii in heart valve tissue from patients with culture-negative infective endocarditis

Coxiella burnetii is a common cause of blood culture-negative infective endocarditis (IE). Molecular detection of C burnetii DNA in clinical specimens is a promising method of diagnosing Q fever endocarditis. Here, we examined the diagnostic utility of Q fever polymerase chain reaction (PCR) of formalin-fixed heart valve tissue from patients with blood culture-negative IE who underwent heart valve surgery. Clinical and laboratory data of patients with blood culture-negative IE who underwent heart valve surgery during a 6-year period and for whom biopsy tissues were available were reviewed retrospectively. Blood culture-positive IE patients who underwent heart valve surgery within the last 3 years were used as controls. Heart valve samples were cultured and also subjected to histological examination and PCR for Q fever, brucellosis, and bartonellosis. Data from 20 patients with blood culture-negative IE and 20 with blood culture-positive IE were analyzed. Eight cases of blood culture-negative IE were PCR-positive for C burnetii (40%; 95% confidence interval, 19-64). No specimen was PCR-positive for brucellosis or bartonellosis. Histologically, 4 of 8 specimens with a positive Q fever PCR result were characterized by clusters of multinucleated giant cells without a fibrin ring. None of 20 patients with blood culture-negative IE received anti-Coxiella antibiotic therapy due to lack of clinical suspicion. Six-month mortality was higher in the Q fever PCR-positive group than in the Q fever PCR-negative group [38% (3/8) vs 0% (0/12), P = .049). Of the 20 patients with blood culture-positive IE, none yielded a positive Q fever PCR result for valve tissue. Approximately 40% of patients with culture-negative IE who received heart valve surgery were PCR-positive for Q fever; patients without clinical suspicion suffered high mortality. These data suggest that Q fever IE in patients with culture-negative IE is often missed in routine clinical practice.

Bartonella Species, an Emerging Cause of Blood-Culture-Negative Endocarditis

Since the reclassification of the genus Bartonella in 1993, the number of species has grown from 1 to 45 currently designated members. Likewise, the association of different Bartonella species with human disease continues to grow, as does the range of clinical presentations associated with these bacteria. Among these, blood-culture-negative endocarditis stands out as a common, often undiagnosed, clinical presentation of infection with several different Bartonella species. The limitations of laboratory tests resulting in this underdiagnosis of Bartonella endocarditis are discussed. The varied clinical picture of Bartonella infection and a review of clinical aspects of endocarditis caused by Bartonella are presented. We also summarize the current knowledge of the molecular basis of Bartonella pathogenesis, focusing on surface adhesins in the two Bartonella species that most commonly cause endocarditis, B. henselae and B. quintana. We discuss evidence that surface adhesins are important factors for autoaggregation and biofilm formation by Bartonella species. Finally, we propose that biofilm formation is a critical step in the formation of vegetative masses during Bartonella-mediated endocarditis and represents a potential reservoir for persistence by these bacteria.

Reassessment of blood culture-negative endocarditis: its profile is similar to that of blood culture-positive endocarditis

INTRODUCTION AND OBJECTIVES

Left-sided infective endocarditis with blood culture-negative has been associated with delayed diagnosis, a greater number of in-hospital complications and need for surgery, and consequently worse prognosis. The aim of our study was to review the current situation of culture-negative infective endocarditis.

METHODS

We analyzed 749 consecutive cases of left-sided infective endocarditis, in 3 tertiary hospitals from June 1996 to 2011 and divided them into 2 groups: group I (n=106), blood culture-negative episodes, and group II (n=643) blood culture-positive episodes. We used Duke criteria for diagnosis until 2002, and its modified version by Li et al. thereafter.

RESULTS

Age, sex, and comorbidity were similar in both groups. No differences were found in the proportion of patients who received antibiotic treatment before blood culture extraction between the 2 groups. The interval from symptom onset to diagnosis was similar in the 2 groups. The clinical course of both groups during hospitalization was similar. There were no differences in the development of heart failure, renal failure, or septic shock. The need for surgery (57.5% vs 55.5%; P=.697) and mortality (25.5% vs 30.6%; P=.282) were similar in the 2 groups.

CONCLUSIONS

Currently, previous antibiotic therapy is no longer more prevalent in patients with blood culture-negative endocarditis. This entity does not imply a delayed diagnosis and worse prognosis compared with blood culture-positive endocarditis. In-hospital clinical course, the need for surgery and mortality are similar to those in patients with blood culture-positive endocarditis. Full English text available from:www.revespcardiol.org.

Management of infective endocarditis: challenges and perspectives

Despite improvements in medical and surgical therapies, infective endocarditis is associated with poor prognosis and remains a therapeutic challenge. Many factors affect the outcome of this serious disease, including virulence of the microorganism, characteristics of the patients, presence of underlying disease, delays in diagnosis and treatment, surgical indications, and timing of surgery. We review the strengths and limitations of present therapeutic strategies and propose future directions for better management of endocarditis according to the most recent research. Novel perspectives on the management of endocarditis are emerging and offer hope for decreasing the rate of residual deaths by accelerating the process of diagnosis and risk stratification, reducing delays in starting antimicrobial therapy, rapid transfer of high-risk patients to specialised medico-surgical centres, development of new surgical methods, and close long-term follow-up.

Infective endocarditis and osteomyelitis caused by Cellulomonas: a case report and review of the literature

Cellulomonas spp. are often believed to be of low virulence and have never been reported as a pathogen causing human disease before. We report the first case of endocarditis caused by Cellulomonas and complicated with osteomyelitis of the lumbar spine in a 78-year-old woman. General weakness and aggravated lower back pain followed by sudden-onset of fever and chills were the major presentation. The diagnosis of infective endocarditis in this case was definitely using the Duke criteria. The magnetic resonance imaging of the lumbar spine revealed infective spondylodisciitis at an early stage. After a full course of antibiotics treatment, the patient's fever subsided but her lower back pain persisted. A slow clinical response to appropriate antimicrobial agents was characteristic of Gram-positive bacillary endocarditis.

Contribution of systematic serological testing in diagnosis of infective endocarditis

Despite progress with diagnostic criteria, the type and timing of laboratory tests used to diagnose infective endocarditis (IE) have not been standardized. This is especially true with serological testing. Patients with suspected IE were evaluated by a standard diagnostic protocol. This protocol mandated an evaluation of the patients according to the modified Duke criteria and used a battery of laboratory investigations, including three sets of blood cultures and systematic serological testing for Coxiella burnetii, Bartonella spp., Aspergillus spp., Legionella pneumophila, and rheumatoid factor. In addition, cardiac valvular materials obtained at surgery were subjected to a comprehensive diagnostic evaluation, including PCR aimed at documenting the presence of fastidious organisms. The study included 1,998 suspected cases of IE seen over a 9-year period from April 1994 to December 2004 in Marseilles, France. They were evaluated prospectively. A total of 427 (21.4%) patients were diagnosed as having definite endocarditis. Possible endocarditis was diagnosed in 261 (13%) cases. The etiologic diagnosis was established in 397 (93%) cases by blood cultures, serological tests, and examination of the materials obtained from cardiac valves, respectively, in 348 (81.5%), 34 (8%), and 15 (3.5%) definite cases of IE. Concomitant infection with streptococci and C. burnetii was seen in two cases. The results of serological and rheumatoid factor evaluation reclassified 38 (8.9%) possible cases of IE as definite cases. Systematic serological testing improved the performance of the modified Duke criteria and was instrumental in establishing the etiologic diagnosis in 8% (34/427) cases of IE.

Blood culture-negative endocarditis in a reference center: etiologic diagnosis of 348 cases

To identify the current etiologies of blood culture-negative infective endocarditis and to describe the epidemiologic, clinical, laboratory, and echocardiographic characteristics associated with each etiology, as well as with unexplained cases, we tested samples from 348 patients suspected of having blood culture-negative infective endocarditis in our diagnostic center, the French National Reference Center for Rickettsial Diseases, between 1983 and 2001. Serology tests for Coxiella burnettii, Bartonella species, Chlamydia species, Legionella species, and Aspergillus species; blood culture on shell vial; and, when available, analysis of valve specimens through culture, microscopic examination, and direct PCR amplification were performed. Physicians were asked to complete a questionnaire, which was computerized. Only cases of definite infective endocarditis, as defined by the modified Duke criteria, were included. A total of 348 cases were recorded-to our knowledge, the largest series reported to date. Of those, 167 cases (48%) were associated with C. burnetii, 99 (28%) with Bartonella species, and 5 (1%) with rare, fastidious bacterial agents of endocarditis (Tropheryma whipplei, Abiotrophia elegans, Mycoplasma hominis, Legionella pneumophila). Among 73 cases without etiology, 58 received antibiotic drugs before the blood cultures. Six cases were right-sided endocarditis and 4 occurred in patients who had a permanent pacemaker. Finally, no explanatory factor was found for 5 remaining cases (1%), despite all investigations.Q fever endocarditis affected males in 75% of cases, between 40 and 70 years of age. Ninety-one percent of patients had a previous valvulopathy, 32% were immunocompromised, and 70% had been exposed to animals. Our study confirms the improved clinical presentation and prognosis of the disease observed during the last decades. Such an evolution could be related to earlier diagnosis due to better physician awareness and more sensitive diagnostic techniques. As for Bartonella species, B. quintana was recorded more frequently than B. henselae (53 vs 17 cases). For 18 patients with Bartonella endocarditis, the responsible species was not identified. Species determination was achieved through culture and/or PCR in 49 cases and through Western immunoblotting in 22. Comparison of B. quintana and B. henselae endocarditis revealed distinct epidemiologic patterns. The 2 cases due to T. whipplei reflect the emerging role of this agent as a cause of infective endocarditis. Because identification of the bacterium was possible only through analysis of excised valves by histologic examination, PCR, and culture on shell vial, the prevalence of the disease might be underestimated. Among patients who received antibiotic drugs before blood cultures, 4 cases (7%) were found to be associated with Streptococcus species (2 S. bovis and 2 S. mutans) through 16S rDNA gene amplification directly from the valve, which shows the usefulness of this technique in overcoming the limitations of previous antibiotic treatment. Right-sided endocarditis occurred classically in young patients (mean age, 36 yr), intravenous drug users in 50% of cases, and suffering more often from embolic complications. Finally, 5 cases without etiology or explaining factors were all immunocompetent male patients with previous aortic valvular lesions, and 3 of the 5 presented with an aortic abscess. Further investigations should be focused on this group to identify new agents of infective endocarditis.

Impact of a molecular approach to improve the microbiological diagnosis of infective heart valve endocarditis

BACKGROUND

Even today, infective endocarditis (IE) remains a severe and potentially fatal disease demanding sophisticated diagnostic strategies for detection of the causative microorganisms. Despite the use of appropriate laboratory techniques, classic microbiological diagnostics are characterized by a high rate of negative results.

METHODS AND RESULTS

Broad-range polymerase chain reaction (PCR) targeting bacterial and fungal rDNA followed by direct sequencing was applied to excised heart valves (n=52) collected from 51 patients with suspected infectious endocarditis and from 16 patients without any signs of IE during an 18-month period. The sensitivity, specificity, and the positive and negative predictive values for the bacterial broad-range PCR were 41.2%, 100.0%, 100.0%, and 34.8%, respectively, compared with 7.8%, 93.7%, 80.0%, and 24.2% for culture and 11.8%, 100.0%, 100.0%, and 26.2% for Gram staining. Without exception, database analyses allowed identification up to the (sub)species level comprising streptococcal (n=13), staphylococcal (n=4), enterococcal (n=2), and other signature sequences such as Bartonella quintana and Nocardia paucivorans. Fungal ribosomal sequences were not amplified. All valve tissues of the reference group were negative for both PCR and conventional methods, except one sample that was contaminated by molds.

CONCLUSIONS

Culture-independent molecular methods substantially improve the diagnostic outcome of microbiological examination of excised heart valves. Importantly, this was true not only for fastidious, slow-growing, and/or nonculturable microorganisms but also for easy-to-culture pathogens such as streptococci and staphylococci. Both patient management and empiric antibiotic therapy of IE are likely to benefit from improved knowledge of the spectrum of pathogens now causing IE.

A mechanic with a bad valve: blood-culture-negative endocarditis

A 33-year-old man with a known bicuspid aortic valve presented with fever, chills, progressive fatigue, anorexia, and night sweats. Echocardiography confirmed aortic-valve endocarditis, but blood cultures remained negative. Bartonella henselae endocarditis was ultimately confirmed by serology as well as by immunohistochemistry and PCR testing of the excised valve. The patient recovered with appropriate antibiotic therapy. B henselae is a common cause of culture-negative endocarditis. It predominantly affects men with underlying valvular disease, and has a predilection for aortic valves. Diagnosis is usually made serologically and with either tissue culture, immunohistochemistry, or PCR. Treatment of this destructive endocarditis consists of a combination of long-term antibiotic therapy and surgical valve repair. This case is used to discuss the approach towards the treatment of patients with endocarditis that is blood-culture negative.

Causative organisms of infective endocarditis according to host status

A prospective study of infective endocarditis (IE) was conducted between 1994 and 2000 in Marseilles, France, and included 170 definite cases diagnosed with the use of modified Duke criteria. Classification of IE based on the aetiological agent was related to epidemiological characteristics, including age, gender and the nature of the injured valve. Enterococci and Streptococcus bovis were identified more frequently in older subjects (p 0.02), and S. bovis was also associated with mitral valve infection (p 0.03). Streptococcus spp. were found to be associated with native valves (p < 10(-3)), whereas coagulase-negative staphylococci and Coxiella burnetii were associated with intracardiac prosthetic material (p < 0.05). S. bovis and Staphylococcus aureus were the predominant species associated with presumably healthy valves (p < 0.05), whereas oral streptococci caused IE exclusively in patients with previous valve damage. The basic host status of IE patients has been linked to specific microorganisms, and this may be of value when empirical treatment is needed in patients who have received previous antibiotic therapy and whose blood cultures are negative.

Comparative molecular and microbiologic diagnosis of bacterial endocarditis

Sequencing of 16S rDNA, and of sodA_int and rpoB_int in some cases, was applied to DNA from heart valves of 46 patients (36 with definite and 10 with possible endocarditis). Sequence-based identifications were compared with those obtained with conventional methods. Among the 36 definite cases, 30 had positive blood cultures and 6 had negative cultures. Among the 30 positive cases, sequencing of 16S rDNA permitted identification of species (18), genus (8), or neither (4); sodA_int and rpoB_int sequencing was necessary for species identification in 8 cases. Species identifications were identical in only 61.5%, when conventional techniques and DNA sequencing were used. In five of the six blood culture–negative endocarditis cases, sequencing identified Bartonella quintana (3), B. henselae (1), and Streptococcus gallolyticus (1). Our results demonstrate a clear benefit of molecular identification, particularly in cases of blood culture–negative endocarditis and of possible endocarditis, to confirm or invalidate the diagnosis. Moreover, in 19.4% of the definite cases, the improvement in species identification by sequencing led to improved patient management.

Diagnostic methods. Current best practices and guidelines for identification of difficult-to-culture pathogens in infective endocarditis

IE is a serious, life-threatening disease. Because treatment must often be adapted to the pathogen involved, rapid identification of the etiologic agent is critical to successful management of each patient. When difficult-to-culture pathogens are involved, routine microbiologic tests, including blood culture, may remain negative. Because such cases may account for up to 31% of all IE cases, alternative diagnostic approaches are necessary. Among the etiologic agents of culture-negative endocarditis, C burnetii and Bartonella spp play a major role; each is responsible for up to 3% of episodes of IE. The authors therefore recommend the systematic use of specific serologies in all cases of clinically suspected endocarditis. The cross-reactivity between C burnetii, Bartonella spp, and Chlamydia spp is of diagnostic importance because all are potential etiologic agents of endocarditis. However, given that the levels of specific antibodies observed in Bartonella endocarditis are extremely high, low-level cross-reactions with other antigens should not lead to misdiagnosis, provided serology for all suspected agents is performed. When serologic test results are negative for both Bartonella spp and C burnetii, special staining by the Gram, Giemsa, Gimenez, PAS, Warthin-Starry, and Grocott methods may guide the use of new diagnostic tools such as PCR and tissue culture for isolation and identification of the causative agent. Such novel approaches may lead to more comprehensive patient evaluations and the discovery of new etiologic agents of IE.

Usefulness of cytokines interleukin-6 and interleukin-2R concentrations in diagnosing active infective endocarditis involving native valves

The most important diagnostic value in infective endocarditis (IE) is isolation of the causative microorganism. Because premature antibiotic treatment is commonly administered before the assessment of blood cultures, the percentages of isolated microorganisms has decreased significantly within the last decades. Therefore, additional criteria for the diagnosis of IE may be helpful. It was hypothesized that assessment of interleukin-6 (IL-6) and interleukin-2R (IL-2R) may provide new diagnostic criteria for inflammation in IE. IL-6 and IL-2R serum concentrations, white blood cell count (WBC), and C-reactive protein (CRP) were measured in the blood of 47 patients with IE at the time of diagnosis and during treatment. WBC and CRP were elevated in patients with IE at the time of diagnosis. Both parameters were higher (p <0.05) in patients with positive blood cultures when compared with negative cultures. The differences persisted during the first week of treatment (p <0.01). In contrast, IL-6 and IL-2R concentrations were elevated (p <0.001) independently of the status of blood cultures. Serum concentrations of IL-6 and IL-2R decreased continuously during antibiotic treatment. Assessment of IL-6 and IL-2R could thus provide new diagnostic criteria for inflammation in IE, and these interleukins could also be suitable for monitoring the course of inflammation during treatment.

Diagnostic methods current best practices and guidelines for identification of difficult-to-culture pathogens in infective endocarditis

Culture-negative endocarditis currently represents a diagnostic challenge for physicians. Traditional methods such as histology, serology, and culture have been improved and new molecular techniques have been developed to improve the detection of difficult-to-culture agents. Serologic tests for the two most frequent etiologic agents, Coxiella burnetii and Bartonella spp, should be performed first because they can usually be identified easily in this way. The sensitivity of culture for intracellular bacteria has been improved by inoculation of samples in shell vials and by the use of novel tissue cell lines. Recently, universal and species-specific primers have been designated to amplify bacterial DNA directly from resected valves, allowing positive identification.

Diagnostic methods current best practices and guidelines for histologic evaluation in infective endocarditis

Infective endocarditis (IE) often presents diagnostic and therapeutic challenges and continues to cause high morbidity and mortality. Confirmation of the diagnosis of IE is important for the purposes of epidemiologic and clinical studies and is crucial for patient management. Despite recent advances in diagnostic techniques, about 10% of IE cases remain culture-negative. Because pathological examination of cardiac valves to demonstrate vegetations and valvular inflammation remains the gold standard for the diagnosis of IE, the role of the pathologist is often decisive, especially when bacteriologists fail to isolate a microorganism or when a microorganism that has been isolated may be a contaminant. Furthermore, the pathologist may play an important role in identification of previously unknown infectious agents.

An update on infective endocarditis of dental origin

OBJECTIVES

The aim of this study was to analyse the prevalence of dental treatment and oral infections related to the development of infective endocarditis (IE).

METHODS

A retrospective study of 103 cases of IE diagnosed from 1997 to 1999 was conducted in Galicia, Spain.

RESULTS

According to the Duke's endocarditis criteria (1994), 87 cases (84.5%) were considered definite IE. A presumed oral portal of entry was recorded in 12 patients (13.7%). Oral infections were held responsible in six cases while the remaining six had received dental treatment in the previous three months (three tooth extractions, one scaling, one cleaning, one fillings). In eight cases of IE (66.6%) typical oral pathogenic microflora was identified, with Streptococcus viridans being the most frequent. In four patients no previous cardiac disease was recorded.

CONCLUSIONS

These results suggest that prevalence and characteristics of IE cases of dental origin did not change significantly in the last decades. The need for increased oral hygiene and improved dental care should be emphasized on preventing IE of dental origin. Continued education of physicians and dentists on the importance of the knowledge of current prophylactic protocols should also be considered.

Endocarditis due to rare and fastidious bacteria

The etiologic diagnosis of infective endocarditis is easily made in the presence of continuous bacteremia with gram-positive cocci. However, the blood culture may contain a bacterium rarely associated with endocarditis, such as Lactobacillus spp., Klebsiella spp., or nontoxigenic Corynebacterium, Salmonella, Gemella, Campylobacter, Aeromonas, Yersinia, Nocardia, Pasteurella, Listeria, or Erysipelothrix spp., that requires further investigation to establish the relationship with endocarditis, or the blood culture may be uninformative despite a supportive clinical evaluation. In the latter case, the etiologic agents are either fastidious extracellular or intracellular bacteria. Fastidious extracellular bacteria such as Abiotrophia, HACEK group bacteria, Clostridium, Brucella, Legionella, Mycobacterium, and Bartonella spp. need supplemented media, prolonged incubation time, and special culture conditions. Intracellular bacteria such as Coxiella burnetii cannot be isolated routinely. The two most prevalent etiologic agents of culture-negative endocarditis are C. burnetti and Bartonella spp. Their diagnosis is usually carried out serologically. A systemic pathologic examination of excised heart valves including periodic acid-Schiff (PAS) staining and molecular methods has allowed the identification of Whipple's bacillus endocarditis. Pathologic examination of the valve using special staining, such as Warthin-Starry, Gimenez, and PAS, and broad-spectrum PCR should be performed systematically when no etiologic diagnosis is evident through routine laboratory evaluation.

Recognition, management and prophylaxis of endocarditis

Infective endocarditis (IE) remains a disease with high morbidity and mortality. In recent years, a higher frequency of IE has been observed in the elderly, in intravenous drug users and in patients with prosthetic valves. The diverse manifestations of this disease demand a high degree of suspicion from the practitioner, in order to make an early diagnosis. Advances in and increasing use of echocardiography (especially transoesophageal) allow us to identify valvular changes earlier and more precisely. The use of the new Duke's diagnostic criteria, based on clinical manifestations and microbiological and echocardiographic findings, facilitates the diagnosis and categorisation of IE. An increase in staphylococci and other problem pathogens, such as penicillin-resistant streptococci, enterococci resistant to beta-lactams, aminoglycosides and methicillin-resistant staphylococci has been observed. Important changes have also taken place in the management of IE. There is a clear trend towards the use of shorter treatment courses, oral and once-daily regimens and outpatient programmes, all of which aim to reduce costs and provide patients with improved quality of life. Antibiotic prophylaxis for the prevention of IE is still controversial. In the past few years more rational regimens have been used, and indications are now more precise. In spite of all this, however, few cases are prevented and patient compliance to the prophylaxis regimens remains low.

Immunoblotting in the diagnosis of culture negative endocarditis caused by streptococci and enterococci

AIM

To improve the diagnosis of culture negative endocarditis by diagnosing cases due to streptococci and enterococci.

METHODS

Serum samples were immunoblotted against extracts of the commonest streptococci and enterococci. They were selected from patients with a cardiac murmur, persistent pyrexia and at least three negative blood cultures. The presence of patterns of endocarditis species specific antigenic bands was measured and correlated with clinical outcome.

RESULTS

Negative serology was found in 28 patients where the diagnosis of endocarditis was rejected or, if proved, staphylococcal, yeast, Gram negative, systemic lupus erythematosus, due to Q fever or Chlamydia psittaci or nonbacterial thrombotic. Positive serology was found in 27 of the 34 patients where the response to antibiotics suggested streptococcal or enterococcal infection. In 22 of these there was objective evidence of endocarditis. Positive serology was also found in three of four further patients with vegetations at necropsy.

CONCLUSION

The identification of patterns of antibody response on immunoblotting can be used to make a specific diagnosis of streptococcal or enterococcal endocarditis in the absence of positive blood cultures.

Crossed immunoelectrophoresis used for bacteriological diagnosis in patients with endocarditis

Sera from 151 patients suspected of having endocarditis were obtained during a period of 3 1/2 years at Rigshospitalet, Copenhagen. The sera were examined by crossed immunoelectrophoresis for antibodies to bacteria causing endocarditis. The patients were divided into four groups: 1. Patients with definite endocarditis, 2. Patients with culture-negative endocarditis, 3. Patients with uncertain endocarditis, and 4. Patients without endocarditis. In sera from patients suffering from endocarditis caused by viridans streptococci, precipitating antibodies were demonstrated by crossed immunoelectrophoresis (diagnostic specificity = 86%; diagnostic sensitivity = 100%) while other bacterial etiologies of endocarditis were less reliably demonstrated by this method.

Endocarditis caused by Rochalimaea henselae

A case of community-acquired, culture-negative, infective endocarditis was diagnosed in a 57-year-old construction worker. Small, pleomorphic gram-negative rods were seen in Brown-Hopps tissue gram stains and Warthin-Starry silver stains. The organism was identified as Rochalimaea henselae by polymerase chain reaction amplification and sequencing of the 16S rDNA gene sequence. This is the first report of infective endocarditis caused by R henselae.

The febrile parenteral drug user: a prospective study in 121 patients

OBJECTIVE

To determine the most efficient approach to the diagnosis of infective endocarditis (IE) in febrile parenteral drug users (PDUs) and evaluate possible effects of human immunodeficiency virus (HIV) infections or acquired immunodeficiency syndrome (AIDS) on susceptibility to IE and final outcome.

DESIGN

A prospective study of appropriate patients admitted on 149 random sampling days during a 14-month period and review of past experience with IE, HIV, and AIDS admissions to hospital.

SETTING

An urban university hospital.

PATIENTS

Prospectively, 121 febrile PDUs plus an additional 16 found to have IE on nonsampling days during the study period. Retrospectively, all PDUs with IE from 1985 to 1991 and all patients with HIV infections with or without AIDS from July 1990 through December 1991.

MEASUREMENTS

Physical examination, hemograms, urinalysis, blood cultures (plus other body fluids when indicated), echocardiography, laboratory testing for HIV status.

MAIN RESULTS

Five categories of patients were identified: I. Infective endocarditis (n = 16); II. Other infections with bacteremia (n = 21); III. Bacteremia with unidentified source of infection (n = 14); IV. Infections without bacteremia (n = 52); V. Fever of unknown origin (n = 18). Physical findings and standard laboratory testing did not differentiate Group I from any of the other diagnostic categories. Adding additional IE cases from nonstudy days brought the total to 32. Vegetations were found on echocardiography in 94%; blood cultures, available in 30 of 32 instances, were all positive. HIV or AIDS status was not found to alter susceptibility to IE or influence mortality. While hospital admissions for HIV and especially AIDS have continued to increase among PDUs, the number of cases of IE has decreased since 1988 to 1989.

CONCLUSIONS

Based on the high incidence of blood culture positivity and the sensitivity of echocardiography in detecting vegetations in IE, a simple algorithm has been developed for the initial diagnostic management of febrile PDUs admitted with the possible diagnosis of IE. HIV infection, with or without full-blown AIDS, does not appear to affect the incidence or outcome of IE among these patients. Current practices among PDUs may be effecting a decline in IE but not HIV infections.

Infective endocarditis with involvement of the tricuspid valve due to Capnocytophaga canimorsus

A case of endocarditis with vegetations on the tricuspid valve caused by Capnocytophaga canimorsus is described. Extensive diagnostic investigations preceded the diagnosis, including blood cultures, 34 of which were sterile. A possible role of the pulmonary circulation in the negative blood cultures is discussed.

Infective endocarditis in children with congenital heart disease: comparison of selected features in patients with surgical correction or palliation and those without

The diagnostic and prognostic features of 44 episodes of infective endocarditis in 42 children with congenital heart disease were reviewed. Endocarditis occurred in 18 patients who had not had surgical correction or palliation of the defect (non-operated group). There were 26 episodes in 24 patients who had been treated surgically (operated group) (16 open and eight closed cardiac operations). Endocarditis occurred soon after open heart surgery in eight patients and as a late complication in the other 16. It recurred in two patients (operated group). Invasive monitoring and low cardiac output were consistent features in those patients who had endocarditis soon after open heart surgery whereas dental treatment was a common feature in non-operated cases and after closed cardiac operations. Late cases of endocarditis after open heart surgery had various microbiological features that were not typical of infection after dental problems. Gram positive infections occurred in non-operated patients and in those who had had closed cardiac operations. The group that had open heart surgery had infections caused by Gram positive, Gram negative, and anaerobic bacteria and fungi. Fever, anaemia, leucocytosis, and positive blood cultures were the only consistent findings. Vegetations were seen in nine of 12 patients at cross sectional echocardiography. All 12 (four non-operated, one closed, and seven open cases) needed acute surgical treatment. The mortality from infective endocarditis was 17% for non-operated cases, 0% for those who had had closed heart surgery, and 50% for those who had had open heart surgery. Infective endocarditis after open heart surgery differs from that in the other subgroups in terms of microbiology, source of infection, and outcome and its early diagnosis depends on a thorough investigation of minimal symptoms and signs.

Culture negative infective endocarditis

Twenty cases of culture negative infective endocarditis admitted to the Cardiology Department of Green Lane Hospital from 1959 to 1980 out of a total of 265 cases (7.5%), were analysed retrospectively. Cases were included only when adequate proof of endocarditis was available at surgery or postmortem. Indiscriminate use of antibiotics before taking blood cultures was the most common association with failure to obtain positive cultures, seen in 16 of the 20 patients described. Failure to obtain positive cultures in four cases was attributed to inadequate bacteriologic techniques before 1967. Where no antibiotics were given prior to collecting blood cultures and bacteriologic techniques were adequate, proven culture negative endocarditis was virtually unknown. When antibiotics have been given, repeated blood cultures are recommended following withdrawal of antibiotic for at least four days.

Subacute bacterial endocarditis due to Actinobacillus actinomycetemcomitans

Sixteen documented cases of Actinobacillus actinomycetemcomitans endocarditis have been reported in the past 15 years. The characteristic granular growth and the fastidious nature and slow-growing character of this organism decrease the yield of positive blood cultures. Two recently observed cases of subacute endocarditis due to Actinobacillus are reported, one in a patient who required surgical intervention for complications of his disease and the other case associated with an aortic prosthetic valve. The first patient had late embolic complications which are commonly seen with Actinobacillus endocarditis. A review of the literature; including a synoptic table with clinical failures, treatment, and outcome is presented. Unless special care is taken to isolate these slow growing organisms, these cases will be misclassified as culture negative endocarditis.

Role of granulocytes and monocytes in experimental Staphylococcus epidermidis endocarditis

The role of granulocytes and monocytes during the induction and course of Staphylococcus epidermidis endocarditis was investigated by the selective depletion of monocytes with the drug VP16-213 and of both granulocytes and monocytes with nitrogen mustard. The induction of endocarditis was influenced only by the depletion of monocytes: the 50% infective dose differed significantly, being 3.4 X 10(5) CFU in control rabbits and 3.4 X 10(4) CFU in the monocyte-depleted rabbits, whereas no significant differences were found between the latter and those depleted of both granulocytes and monocytes. Also, control rabbits injected with 10(6) or 10(7) CFU had a significantly higher incidence of sterile vegetations than did rabbits selectively depleted of granulocytes or monocytes. Compared with baseline values, mean monocyte numbers at the time of bacterial inoculation were significantly increased in control rabbits whose vegetations remained sterile, whereas this effect was not seen in rabbits whose vegetations became infected. The course of the endocarditis appeared to be significantly influenced by both granulocytes and monocytes. Comparison showed that a decrease of the same numbers of these cells per microliter of blood was accompanied for the monocytes by an approximately fourfold higher increase of the number of staphylococci in the vegetations. The correlation between the number of granulocytes and of monocytes on the one hand and the number of staphylococci in the vegetations on the other was not substantially influenced by the duration of the disease or the number of staphylococci injected to induce the endocarditis. The number injected proved to be significantly correlated with the number of staphylococci in the vegetations. In rabbits with numbers of CFU per gram of vegetation exceeding 10(7), blood cultures were usually positive. This finding applied rarely to control rabbits, but generally to drug-treated rabbits. In the latter animals a significant correlation between the number of staphylococci in the vegetations and in the circulation was found. We conclude that only monocytes have a measurable effect on the induction of Staphylococcus epidermidis endocarditis but during its course both granulocytes and monocytes keep the endocardial infection in check.

Culture-negative infective endocarditis

Culture-negative endocarditis is not uncommon; the most frequent causes of the culture negative state are prior antibiotic therapy and problems with or inadequacies in bacteriologic technique. In addition to blood culture, studies that can aid in substantiating a presumptive diagnosis of infective endocarditis include echocardiography. Immunologic tests, and cardiac catheterization. Empiric antibiotic therapy often is necessary and should not be delayed to await positive blood cultures and results of antimicrobial sensitivity studies.

The use of echocardiography in diagnosing culture-negative endocarditis

We reviewed M-mode and two-dimensional echocardiographic findings in 11 patients with abacteremic endocarditis to study the application of echocardiography in this setting. All patients had negative blood cultures but underwent surgery that confirmed the presence of active infective endocarditis. The infection involved native valves in five patients and prosthetic valves in six patients. Valvular masses were identified in eight patients. The other three patients, who had prosthetic aortic valves, had diastolic mitral valve vibration characteristic of aortic regurgitation. One of these also showed dehiscence of the prosthesis. Three patients had poorly defined clinical illnesses and echocardiography was a prime element in the diagnosis because valvular masses were identified. The operation was facilitated by knowledge of the mass indicated by echocardiography in these eight cases. Also, the surgical approach was affected by knowledge of dehiscence and perivalvular abscess formation in two cases each.

Infected aortic aneurysm

Aortic aneurysms may become infected. This unusual complication carries a highly unfavorable prognosis. In any patient with sepsis and a known aneurysm, spread of the sepsis to the aneurysm should be suspected if no other source of infection can be found. A case report is presented, together with a brief review of the literature.

Fc rosette inhibition by serum of patients with infective endocarditis

The inhibition of lymphocyte Fc rosette formation was studied in sera of patients with infective endocarditis. The pretreatment value of sensitised chicken erythrocyte (EA) rosette inhibition was 37.9 +/- 7.8%; in controls it was 4.1 +/- 1.3% (P less than 0.001). The posttreatment value was 2.8 +/- 2.1%. Six patients had culture-negative infective endocarditis, and in them the value of EA rosette inhibition was higher than in the others (42.3 +/- 7.1%). The measurement of circulating immune complexes may be a diagnostic tool in patients with culture-negative infective endocarditis.

Infective endocarditis with negative blood cultures. An analysis of 52 cases

The clinical records of 52 patients who were diagnosed clinically as having had infective endocarditis despite negative blood cultures have been reviewed. They differed at presentation from patients with positive blood cultures in more frequent receipt of antibiotics prior to culture and more frequent signs of major systemic emboli and congestive heart failure. Response of culture-negative patients with fever to empiric antibiotic therapy was correlated with survival, in that 92 per cent of the patients who became afebrile within the first week of therapy liver, whereas only 50 per cent of those who did not become afebrile lived. Deaths resulted primarily from major systemic emboli and from uncontrollable congestive heart failure due to valvular insufficiency. In 25 cases, valvular tissue was examined histologically. In 15 cases, vegetations were seen and organisms identified; in six cases, only vegetations were seen; and in four cases (16 per cent), the clinical diagnosis of infective endocarditis was not substantiated in the pathologic report.