culture negative is
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CULTURE-NEGATIVE
ENDOCARDITIS
5/3/2012
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Definition
Blood culture-negative IE is defined as endocarditis without
etiology following inoculation of at least three independent
blood samples in a standard blood culture system with
negative cultures after seven days of incubation and
subculturing
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Incidence
Accounts for about 30% of all cases of endocarditis
worldwide
In developed countries-
Netherlands (1%), the USA (5%), Sweden (12%), the UK (15%), France (18%)
In developing countries-
Khan et al (JPMA 60:24; 2010) - 46.7% IE causes were culture
negative ( Pakistan)Ravi et al (Am heart J 2011)- 59% CNE (India)
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Incidence
Variations in incidence accounted for by
(i) differences in the diagnostic criteria used
(ii) specific epidemiological factors, as for fastidious zoonotic
agents
(iii) variations in the early use of antibiotics prior to blood
sampling
(iv) differences in sampling
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Factors Contributing to Sterility of Blood
Cultures
Antibiotic administration preceding blood cultures
More in developing countries due to unrestricted usage and availability of
antibiotics without prescription This situation arises in patients who received antibiotics for
unexplained fever before any blood cultures were performed
and in whom the diagnosis of IE was not considered
Causative organisms are most often oral streptococci , S.aureus or CNS.
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Factors Contributing to Sterility of
Blood Cultures
Impact of Taking Antibiotics Before Blood Cultures Are Obtained
It¶s the leading cause of BC-negative IE.
Reduces the recovery rate of bacteria by 35-40%.
The length of time the cultures will remain negative is determined by
the susceptibility of the organism and the duration of antibiotic use
before blood cultures are drawn.
Cultures of pts who receive longer course of high dose, bactericidalantibiotics may remain negative for weeks.
If the initial cultures were negative after only a few days of antibiotics,
infective endocarditis pts may have a positive bacterial culture after
only several days without antibiotics.
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Factors Contributing to Sterility of Blood
Cultures
Fastidious slow-growing bacteria
Nutritionally variant streptococci, fastidious Gram-negative bacilli
of the HACEK group (Haemophilus parainfluenzae,
Aggregatibacter(previously Hemophilus) aphrophilus,
Aggregatibacter (previouslyActinobacillus )
actinomycetemcomitans,
Cardiobacterium hominis, Eikenella corrodens, Kingella kingae)and Brucella
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Factors Contributing to Sterility of Blood
Cultures
Intracellular bacteria
As Coxiella burnetii, Bartonella, Chlamydia, Tropheryma whipplei,
the agent of Whipple¶s disease
Non-bacterial organisms i.e. fungi
Patient factors
Prosthetic valves, renal failure, Pacemakers, Indwelling
intravenous catheters, immunocompromised states
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Non-Infectious Causes of CNE
2.5% of CNE in recent series
Antiphospholipid syndrome: Primary or Secondary (e.g. SLE or
malignancies)
Neoplasia Associated:Atrial Myxoma, Marantic endocarditis,Carcinoid
AI associated: Rheumatic carditis, SLE, PA N, Behcet¶s disease
Postvalvular surgery: Thrombus, stitch, or other postsurgical
changes Miscellaneous: eosinophilic heart disease, ruptured mitral chordae,
myxomatous degeneration
Fournier et al. CID. 2010
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Factors Contributing to Sterility of
Blood Cultures
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Modified Duke criteria
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Modified Duke criteria
By applying serology in Dukes criteria
8.9% patients upgraded from possible IE to definite IE
7.3% patients upgraded from rejected IE to possible IE
J Clin Microbiol 2005:43
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Possible microbiological causes of CNE
HACEK organisms- traditionally thought to be the common
agents of culture-negative endocarditis but can be easily
isolated with current blood culture systems when incubated for
at least five days
The most common agents of CNE are fastidious organisms
(eg, zoonotic agents and fungi) and Streptococcal spp. in
patients who have received previous antibiotic treatment.
C. burnetii - a relatively common cause of IE in Europeancountries
Bartonella
Fungi
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Possible microbiological causes of CNE
Coxiella burnetii 3-48%
Bartonella species 10-28%
Staphylococcus species 2-11%
Streptococcus species 1-6%
HACEK 0.5-3%
Fungi 1-6%
Candida,Aspergillus, Cryptococcus, endemic fungi, others
Tropheryma whipplei 0.3-3%
Others: Legionella, Chlamydia, Brucella
Fournier. CID.
2010;96.
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When to suspect ..
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In India
C. burnetii and Bartonella spp. were responsible for
8% of all infectious endocarditis cases and 14% of
blood culture±negative cases (Chennai)Emerg Infect Dis. 2008 July; 14(7): 1168±1169
There are also reports of brucella, trophyrema
(whipple¶s) endocarditis in India.
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Value of positive cultures
Positive cultures have been a cornerstone in the diagnosis of
IE
Selection of appropriate antibiotic therapy based on thesensitivity pattern
Requirement to cover all likely organisms (in CNE) ±
increased chances of drug toxicities
Reported increased mortality and complications of CNE insome series
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To increase yield of cultures
Avoid prior antibiotic usage
Atleast 3 sets
Blood subcultures on chocolate agar
Prolonged incubation may be needed
If the patient is clinically stable , antibiotics can be withheld
awaiting fresh cultures
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Diagnosis
Special culturing techniques (eg, shell vial and lysis
centrifugation)
Molecular techniques (eg, polymerase chain reaction) Serologic assays
Histopathology evaluation of valvular tissue when surgical
excision is performed
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Molecular techniques
Polymerase chain reaction ± most data for diagnosis of CNE
come from its use in the setting of explanted valve tissue but
can also be used in serum..
There are broad-range PCR techniques for amplifying16SrDNA (for bacteria) or 18SrDNA (for fungi), which can
then be sequenced for pathogen identification
The most frequently identified bacteria have included
streptococci, staphylococci, Bartonella spp., and T. whipplei .
There are real-time PCR techniques for diagnosis of specific
pathogens including Bartonella spp., C. burnetii (Q fever), and
Whipple's disease
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Molecular techniques
Sensitivity of PCR for pathogen identification in CNE ranges
from 40 to 60 percent, with specificity nearing 100 percent
Limitations
False negative results - preoperative antibiotics, which probably decreasethe diagnostic yield of valve tissue PCR
False positive results - persistent nonviable bacteria months or years after
apparent cure , if valve tissue is contaminated in the process of surgical
removal or transport
³ A positive PCR test from valve tissue must be correlated with theknown propensity of the detected microbe to cause IE´
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Serologic assays
The etiologic agents in culture-negative IE best identified by
serology include Coxiella burnetii, Bartonella spp.,
Chlamydophila (formerly Chlamydia) spp., Legionella spp.,
and Brucella spp
Coxiella burnetii phase I antibody titers >800 are diagnostic
for Q fever endocarditis
Bartonella IgG levels 800 are diagnostic for Bartonella spp.
IE . However, patients with Q fever may have low-level cross-
reacting antibodies to Bartonella spp. and/or Chlamydophila
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Special culture techniques
Lysis centrifugation - improve yield of fastidious organisms
(eg, Brucella spp. and fungi) . This culture system contains
components that lyse leukocytes and erythrocytes, as well as
inactivate plasma complement and certain antibiotics, allows
release of intracellular microorganisms, and the centrifugation
step concentrates the organisms which can then be plated
directly onto supportive medium.
Shell vial cell culture - Of blood or excised heart valves
allows the isolation of Coxiella burnetii, Bartonella spp., T.whipplei, and Brucella spp. and has been useful in identifying
the etiologic agent in CNE.
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Histopathology
Can be useful for pathogen identification of infectious
endocarditis as well as noninfectious mimickers includingmarantic endocarditis, rheumatic endocarditis, myxoma and
others.
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Multimodal strategy
Comprehensive Diagnostic Strategy for Blood Culture±Negative
Endocarditis:A Prospective Study of 819 New Cases. Fournier et al CID
2010
Multimodal strategy incorporating serological, molecular, and
histopathological assays to investigate specimens from 819 patientssuspected of having BCNE
A causative microorganism was identified in 62.7%, and a noninfective
etiology in 2.5%
Blood was the most useful specimen, providing a diagnosis for 47.7% of
patients by serological analysis (mainly Q fever and Bartonella infections)
PCR of blood and Bartonella±specific Western blot methods diagnosed 7
additional cases. PCR of valvular biopsies identified 109 more etiologies,
mostly streptococci, Tropheryma whipplei, Bartonella species, and fungi
Histological analysis or searching for antinuclear antibodies yielded non
infectious cause in 2.5% of the patients
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Therapy
Suspected NVE with confounding antibiotic therapy
Ampicillin ± Sulbactam plus Gentamycin
Or
Vancomycin plus Gentamycin and Ciprofloxacin
Suspected PVE
Vancomycin plus Gentamycin, Cefepime and Rifampicin
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Therapy
If no response to empirical antibiotic therapy,
surgical intervention both as therapy and to obtain
specimens is recommended.