Infective endocarditis: improving the diagnostic yield.
BACKGROUND
Isolating aetiological agents in patients with infective endocarditis (IE) remains problematical. We postulated that the high local incidence of culture-negative IE resulted from antibiotic exposure prior to blood cultures and that a structured delay in therapy in the subacute presentation would improve the diagnostic yield.


OBJECTIVE
We aimed to prospectively observe the diagnostic approach and give an overview of supplementary laboratory tests.


METHODS
Patients with suspected IE were enrolled into this analytical observational study and followed up for six months (n = 92). We compared the diagnostic yield and outcome in cases where antibiotics were withheld for 72 hours, with those cases who received early antimicrobials, despite being deemed safe for delayed therapy.


RESULTS
Definitive diagnoses (definite or excluded IE) were made in 92.8% of patients where antibiotics were delayed, compared to 60% of patients who received empirical treatment (p = 0.08). The mortality rates were 18.4% and 30.0% (p = 0.18). Twenty-three of 26 patients with definite culture-negative IE received antibiotics during the 48 hours preceding cultures, compared to eight of 21 culture-positive patients (P < 0.001). Screening for atypical bacteria did not improve the yield. C-reactive protein (CRP) had a sensitivity of 97.0% (negative predictive value 87.5%), whereas a positive rheumatoid factor (RF) had a specificity of 93.8% (positive predictive value 91.7%).


CONCLUSIONS
We observed tendencies towards a greater diagnostic yield and lower mortality where antibiotics were initially withheld. Antibiotic prior to blood cultures were an important cause of culture-negative IE. A normal CRP proved useful in excluding IE; a positive RF strongly favoured IE.
Department of Internal Medicine, University of Stellenbosch, and Tygerberg Academic Hospital, Western Cape, South Africa.
C F N
CF
Koegelenberg
A F
AF
Doubell
H
H
Orth
H
H
Reuter
D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000378:metabolism; D003937:Diagnosis, Differential; D004697:Endocarditis, Bacterial / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology* / Q000401:mortality; D005500:Follow-Up Studies; D006090:Gram-Negative Bacteria / Q000302:isolation & purification; D016905:Gram-Negative Bacterial Infections / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology* / Q000401:mortality; D006094:Gram-Positive Bacteria / Q000302:isolation & purification; D016908:Gram-Positive Bacterial Infections / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology* / Q000401:mortality; D006801:Humans; D015994:Incidence; D008945:Mitral Valve Prolapse / Q000175:diagnosis / Q000188:drug therapy / Q000382:microbiology; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012214:Rheumatic Heart Disease / Q000175:diagnosis / Q000188:drug therapy / Q000382:microbiology; D012217:Rheumatoid Factor / Q000378:metabolism; D012680:Sensitivity and Specificity; D013019:South Africa / Q000453:epidemiology; D016019:Survival Analysis
D000900:Anti-Bacterial Agents; D015415:Biomarkers; D002097:C-Reactive Protein; D012217:Rheumatoid Factor