**3.1. Definition**

*Pathological criteria*: Microorganisms demonstrated by culture or on histological examination of a vegetation, a vegetation that has embolized, or an intracardiac abscess specimen; or pathological lesions; vegetation or intracardiac abscess by histological examination showing active endocarditis.

*Clinical criteria*: two major criteria; or one major criterion and three minor criteria or five minor criteria.

**3.2. Past history and clinical examination**

**Major criteria**

**1.** Blood cultures positive for IE

**2.** Imaging positive for IE

**Minor criteria**

Duke criteria.

**a.** Typical microorganisms consistent with IE from two separate blood cultures \**Streptococcus viridance*, *Streptococcus bovis*, HACEK group, *Staphylococcus aureus*

**b.** Microorganisms consistent with IE from persistently positive blood cultures defined as follows

**c.** Single positive blood culture for *Coxiella burnetii* or phase I IgG antibody titer>1:800

prosthesis was implanted for 3 months) or radiolabeled leukocytes SPECT/CT.

\*All of 3 or a majority of >4 separate cultures of blood (with first and last samples (drawn>1 h apart)

**a.** Echocardiogram positive for IE: vegetation, abcess, pseudoaneurysm, intracardiac fistula, valvular perforation

Blood Culture-Negative Endocarditis http://dx.doi.org/10.5772/intechopen.76767 61

**b.** Abnormal activity around the site of prosthetic valve implantation detected by 18F-FDG PET/CT (only if the

**3.** Valvular phenomena (including those detected by imaging only) major arterial emboli, septic pulmonary infarcts, infectious (mycotic) aneurysm, intracranial hemorrhages, conjunctival hemorrhages and Janeway's lesions. **4.** Microbiological evidence: positive blood culture but does not meet a major criterion as noted above or serological

CT, computed tomography; FDG, fluorodeoxyglucose; HACEK, Haemophilus parainfluenzae, H. aphrophilus, H. paraphrophilus, H. influenzae, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae, and K. denitrificans; IE, infective endocarditis; Ig, immunoglobulin; PET, positron emission

**Table 1.** Definitions of the terms used in the European Society of Cardiology 2015 modified criteria adapted from modified

\*Community-acquired enterococci, in the absence of a primary focus

\*>2 positive blood cultures of blood samples drawn >12 h part; or

or aneurysma, new partial dehiscence of prosthetic valve

**1.** Predisposition such as predisposing heart condition, or injection drug use.

evidence of active infection with organism consistent with IE

tomography; SPECT, single photon emission computerized tomography.

**c.** Definite paravalvular lesion by cardiac CT.

**2.** Fever defined as temperature > 38°C

defining the etiology of BCNIE are shown in **Table 2** [1].

A precise interview about epidemiological factors, history of prior infections, exposure to

Previous exposure to antibiotics is the most common cause of BCNE, and even a short course of antibiotics can cause long-lasting suppression of bacterial activity. A history of animal exposures may predispose to certain microbiologic etiologies. Immunosuppression or prolonged antibiotic therapy suggests endocarditis due to fungi. The epidemiological clues for

antimicrobials, should be made in all patients with suspected BCNIE [1, 4].

*Possible IE*: One major criterion and one minor criterion or three minor criteria.

*Rejected IE*: Firm alternate diagnosis; or Resolution of symptoms suggesting IE with antibiotic therapy for ≤4 days; or No pathological evidence of IE at surgery or autopsy, with antibiotic therapy for ≤4 days; or Does not meet criteria for possible IE, as above.

When blood culture is negative, systematic diagnostic approach should be performed for rapid and correct management of BCNIE. Diagnostic work-up in blood culture-negative endocarditis is shown in **Figure 1** [1, 4].

#### **Major criteria**

patients with confirmed IE had negative blood cultures [2]. BCNIE often produces considerable

**2.** Endocarditis related to fastidious microorganisms in which prolonged incubation is

**3.** True blood culture-negative endocarditis, due to intra-cellular bacteria that cannot be de-

If all microbiological assays are negative, noninfective endocarditis is considered, and systematically differential diagnosis should be performed. Nonbacterial thrombotic endocarditis (marantic endocarditis) in patients with malignant tumor and systemic diseases such as SLE

Definitions of the terms used in the European Society of Cardiology 2015 [4] modified criteria adapted from modified Duke Criteria [3] were shown in **Table 1**. Diagnosis of IE is drawn as

*Pathological criteria*: Microorganisms demonstrated by culture or on histological examination of a vegetation, a vegetation that has embolized, or an intracardiac abscess specimen; or pathological lesions; vegetation or intracardiac abscess by histological examination showing

*Clinical criteria*: two major criteria; or one major criterion and three minor criteria or five minor

*Rejected IE*: Firm alternate diagnosis; or Resolution of symptoms suggesting IE with antibiotic therapy for ≤4 days; or No pathological evidence of IE at surgery or autopsy, with antibiotic

When blood culture is negative, systematic diagnostic approach should be performed for rapid and correct management of BCNIE. Diagnostic work-up in blood culture-negative

*Possible IE*: One major criterion and one minor criterion or three minor criteria.

therapy for ≤4 days; or Does not meet criteria for possible IE, as above.

diagnostic and therapeutic dilemmas, which result in poor prognosis.

**1.** Administration to antimicrobial agents before blood culture.

tected by currently available routine blood culture system.

and Behҫet are two main causes of noninfective endocarditis.

**2. Main etiologies of BCNIE**

60 Advanced Concepts in Endocarditis

necessary.

**3. Diagnostic approach**

follows:

criteria.

**3.1. Definition**

active endocarditis.

endocarditis is shown in **Figure 1** [1, 4].

There are three main causes for BCNIE.

	- **a.** Typical microorganisms consistent with IE from two separate blood cultures

\**Streptococcus viridance*, *Streptococcus bovis*, HACEK group, *Staphylococcus aureus*

\*Community-acquired enterococci, in the absence of a primary focus

**b.** Microorganisms consistent with IE from persistently positive blood cultures defined as follows

\*>2 positive blood cultures of blood samples drawn >12 h part; or


#### **2.** Imaging positive for IE


#### **Minor criteria**


CT, computed tomography; FDG, fluorodeoxyglucose; HACEK, Haemophilus parainfluenzae, H. aphrophilus, H. paraphrophilus, H. influenzae, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae, and K. denitrificans; IE, infective endocarditis; Ig, immunoglobulin; PET, positron emission tomography; SPECT, single photon emission computerized tomography.

**Table 1.** Definitions of the terms used in the European Society of Cardiology 2015 modified criteria adapted from modified Duke criteria.

#### **3.2. Past history and clinical examination**

A precise interview about epidemiological factors, history of prior infections, exposure to antimicrobials, should be made in all patients with suspected BCNIE [1, 4].

Previous exposure to antibiotics is the most common cause of BCNE, and even a short course of antibiotics can cause long-lasting suppression of bacterial activity. A history of animal exposures may predispose to certain microbiologic etiologies. Immunosuppression or prolonged antibiotic therapy suggests endocarditis due to fungi. The epidemiological clues for defining the etiology of BCNIE are shown in **Table 2** [1].

**Figure 1.** Diagnostic workup in blood culture-negative endocarditis.

#### **3.3. Blood culture**

BCNIE occurs frequently (45–60%) by common and easily grown staphylococci or streptococci in patients with preceding administration of antibiotics as it reduces the recovery rate of bacteria by 35–40% [5, 6]. In these cases, withdrawing antibiotics and repeating blood cultures are preferable methods to diagnose if the patient status allowed. The use of specific blood culture bottles for fastidious microorganisms is not recommended recently [1, 4, 5]. The extended incubation is applied only when cultures remain sterile after 48–72 h. Sophisticated automated systems allow isolating most pathogens that can grow slowly including Candida sp., deficient streptococci and HACEK group bacteria(Haemophilus, Aggregatibacter (previously Actinobacillus), Cardiobacterium, Eikenella, Kingella). Extending culture beyond 5 days is not contributive [1, 4–8]. The popular pathogens such as staphylococci, streptococci and enterococci are usually identified within 48 h. The European guidelines recommend that clinicians require prolonged incubation of vials only in the rare cases of cultures remaining negative at

**Table 2.** Epidemiological clues for defining the etiology of blood culture-negative infective endocarditis *S. aureus*, *Staphylococcus aureus*; CNS, coagulase -negative staphylococci; *S. gallolytics*, *Streptococcus gallolyticus*; *Streptococcus* 

The list of serological tests to be performed in case of blood culture-negative endocarditis used to include: *Legionella pneumophila*, *Mycoplasma hominis*, *Chlamydophila pneumoniae*, Brucella sp., *Coxiella burnetii* (*C. burnetii*), and Bartonella sp. Two major series showed that only Bartonella sp. and *C. burnetii* serological tests are contributive: 348 cases of suspected BCNIE were investigated between 1983 and 2001, the diagnosis was documented by serological tests in 268 cases (77%),

48–72 h and if the diagnosis of IE remains plausible [4, 8].

**Epidemiological feature Suspected microorganisms**

Exposure to dog and/or cat *Bartonella sp.,Pasteurella sp.*

Intravenous drug use, cardiovascular

Contact with contaminated milk or farm

Contact with contaminated milk or

infected farm animals

Homeless, body lice *Bartonella sp.*

Homeless, body lice *Bartonella sp.*

medical devices

animal

Alcoholism, Cirrhosis *Bartonella sp., Aeromnas sp.*, *Listeria sp.*

Chronic skin disorders *S. aureus*, β-hemolytic streptococci

Burn *S. aureus*, Aerobic Gram-negative bacilli, Fungi

Fungi

Genitourinary disorders Enterococcus, GroupB streptococci, aerobic Gram-negative bacilli, *Neisseria gonorrhoeae*, Listeria monocytoogenes

Prosthetic valve replacement Early(<1y): CNS, *S. aureus*, Aerobic Gram-negative bacilli, Fungi,

*Brucella sp.*, Cociella bumetii

*Brucella sp., Coxiella bumetii, Erysipelothrix sp.*

Gastrointestinal lesions *S. gallolytics* (bovis), *Enterococcus sp.,* Clostridium spectrum

Dog or cat exposure *Bartonella sp., Pasteurella sp., Capnocytophaga sp.*

Diabetes mellitus *S. aureus*, β-Hemolytic streptococci, *S. pneumoniae*

Organ transplantation *S. aureus, Aspergillus fumigatus, Enterococcus sp., Candida sp.*

AIDS *Salmonella sp., S. pneumoniae, S. aureus*

*S. aureus*, CNS, Aerobic Gram-negative bacilli, β-Hemolytic streptococci,

Blood Culture-Negative Endocarditis http://dx.doi.org/10.5772/intechopen.76767 63

*Corynebacterium sp., Legionella sp*., Late(>1y): CNS, *S. aureus*, Viridance

*Streptcoccus sp*., Enterococcus sp., Fungi, Corynebacterium

**3.4. Serology**

*pneumonie*.


**Table 2.** Epidemiological clues for defining the etiology of blood culture-negative infective endocarditis *S. aureus*, *Staphylococcus aureus*; CNS, coagulase -negative staphylococci; *S. gallolytics*, *Streptococcus gallolyticus*; *Streptococcus pneumonie*.

Actinobacillus), Cardiobacterium, Eikenella, Kingella). Extending culture beyond 5 days is not contributive [1, 4–8]. The popular pathogens such as staphylococci, streptococci and enterococci are usually identified within 48 h. The European guidelines recommend that clinicians require prolonged incubation of vials only in the rare cases of cultures remaining negative at 48–72 h and if the diagnosis of IE remains plausible [4, 8].

#### **3.4. Serology**

**3.3. Blood culture**

62 Advanced Concepts in Endocarditis

**Figure 1.** Diagnostic workup in blood culture-negative endocarditis.

BCNIE occurs frequently (45–60%) by common and easily grown staphylococci or streptococci in patients with preceding administration of antibiotics as it reduces the recovery rate of bacteria by 35–40% [5, 6]. In these cases, withdrawing antibiotics and repeating blood cultures are preferable methods to diagnose if the patient status allowed. The use of specific blood culture bottles for fastidious microorganisms is not recommended recently [1, 4, 5]. The extended incubation is applied only when cultures remain sterile after 48–72 h. Sophisticated automated systems allow isolating most pathogens that can grow slowly including Candida sp., deficient streptococci and HACEK group bacteria(Haemophilus, Aggregatibacter (previously

The list of serological tests to be performed in case of blood culture-negative endocarditis used to include: *Legionella pneumophila*, *Mycoplasma hominis*, *Chlamydophila pneumoniae*, Brucella sp., *Coxiella burnetii* (*C. burnetii*), and Bartonella sp. Two major series showed that only Bartonella sp. and *C. burnetii* serological tests are contributive: 348 cases of suspected BCNIE were investigated between 1983 and 2001, the diagnosis was documented by serological tests in 268 cases (77%), including 266 cases of *C. burnetii* (n = 167) or Bartonella sp. (n = 99) [5]. The same team reported a second series of 745 patients presenting with suspected BCNIE having received a panel of serological tests between 2001 and 2009. They documented the predominance of Q fever and Bartonellosis. A total of 354 of the 356 cases documented by serological tests were positive for *C. burnetii* (n = 274) or Bartonella sp. (n = 80) [6]. In other words, if only Bartonella sp. and *C. burnetii* serological tests had been used, only 4 out of 624 diagnoses obtained by serological tests would have been missed. A review of endocarditis caused by fastidious pathogens shows that Mycoplasma sp. endocarditis is very rare (<10 reliable observations published to date, mostly due to M. hominis), as well as Legionella sp. endocarditis [7]. Moreover, most cases of endocarditis supposedly due to Chlamydophila sp. are probably cross-reactions with a Bartonella sp. In 2015, the only routinely recommended serological tests in case of negative blood cultures are tests for Q fever and Bartonellosis [4]. Brucellosis serological tests can be added in case of risk factors (living in endemic areas, occupational exposure, consumption of nonpasteurized dairy products). Serological tests for Mycoplasma sp. and Legionella sp. are still recommended in the 2015 ESC guidelines [4].

**4. Treatment**

**4.1. Empirical therapy**

is recommended for the specific pathogen identified.

**4.2. Antibiotic treatment for fastidious microorganisms**

Selection of medical therapy for patients with BCNIE is difficult. Some of the laboratorybased diagnostic techniques to define fastidious or rare pathogens are not available in most clinical laboratories. It consumed considerable time for completion of testing if specimens are sent to a referral laboratory. Patients with BCNIE are often treated empirically for the more common bacterial causes of IE during the waiting time. There is a need to provide empirical antimicrobials for all likely pathogens, though certain therapeutic agents, including aminoglycosides, have potentially toxic effects. Consultation with an ID specialist to define the most appropriate choice of therapy is recommended. Once additional clinical and laboratory data were brought, initial empirical therapy should be changed to more specific treatment. For patients with acute (days) clinical presentations of native valve infection, coverage for S aureus*,* β-hemolytic streptococci, and aerobic Gram-negative bacilli is reasonable. Empirical coverage could include vancomycin and cefepime as an initial regimen [1, 4, 14]. For patients with a subacute (weeks) presentation of native valve IE, empirical coverage of *S. aureus*, Viridance group streptococci (VGS), HACEK, and enterococci is reasonable. One treatment option could include vancomycin and ampicillin-sulbactam to provide some coverage for these organisms [1, 4, 14]. For patients with culture-negative prosthetic valve IE, coverage for staphylococci, enterococci, and aerobic Gram-negative bacilli is reasonable if the onset of symptoms is within 1 year of prosthetic valve placement. A regimen could include vancomycin, rifampin, gentamicin [1, 4, 14]. If symptom onset is >1 year after valve placement, then IE is more likely to be caused by staphylococci, VGS, and enterococci, and antibiotic therapy for these potential pathogens is reasonable [1, 4, 14]. One initial treatment option could include vancomycin and ceftriaxone. If subsequent blood culture results or other laboratory methodologies define a pathogen, then empirical therapy should be changed to focused therapy that

Blood Culture-Negative Endocarditis http://dx.doi.org/10.5772/intechopen.76767 65

HACEK Gram-negative bacilli are fastidious organisms, and the laboratory should be made aware that infection with these agents needs consultation to specialist. Because of slow growth, standard MIC tests may be difficult to interpret. Some HACEK-group bacilli produce betalactamases, and ampicillin is therefore no longer the first-line option. They are susceptible to ceftriaxone, other third-generation cephalosporins and quinolones; the standard treatment is ceftriaxone 2 g/day for 4 weeks in native valve endocarditis and for 6 weeks in prosthetic valve endocarditis. If they do not produce beta-lactamase, ampicillin (12 g/day i.v. in four or six doses) plus gentamicin (3 mg/kg/day) divided into two or three doses for 4–6 weeks is an option [1, 4, 13]. Ciprofloxacin (400 mg/8–12 h i.v. or 750 mg/12 h orally) is a less well-

In cases with fungi, mortality is very high, and treatment necessitates combined antifungal administration and surgical valve replacement. Antifungal therapy for Candida sp. includes liposomal amphotericin B with or without flucytosine or an echinocandin at high doses; and for Aspergillus spp., voriconazole is the drug of choice and some experts recommend the addition

validated alternative. Clinical outcome of HACEK endocarditis is favorable.

#### **3.5. Evaluation of valve tissue**

The more frequent use of valve replacement in the acute phase of infective endocarditis and the advent of molecular biology techniques have revolutionized the diagnosis of blood culture-negative endocarditis:

PCR systems based on universal bacterial 16S ribosomal RNA have demonstrated excellent sensitivity and specificity [8, 9], as well as PCR targeting bacteria specifically responsible for endocarditis with negative blood culture: Bartonella sp., *C. burnetii* [10] and *Tropheryma whipplei* (*T. whipplei*) [11].

Moreover, the microscopic examination of valves after Gram staining, and cultures on appropriate media provide important information not only for the identification of the pathogen involved when the data were not available preoperatively [12], but also information on its viability at the time of valve replacement, which will impact the duration of post-replacement treatment [11, 13]. The histological analysis of valves is not contributive to diagnose except some rare diagnoses such as porcine bioprosthesis endocarditis mediated by allergy to porcine proteins [22, 23]. Summary of diagnostic procedure of rare pathogens of BCNIE is shown in **Table 3**.


**Table 3.** Summary of diagnostic procedure of rare pathogens of blood culture-negative infective endocarditis.
