Bacteremic Streptococcus bovis infections at a university hospital, 1992-2001

Abstract

Background and purpose: The association of Streptococcus bovis biotypes with types of clinical infection and underlying malignancies has rarely been reported in Taiwan. The aim of this study was to characterize the clinical features and microbiological characteristics of patients with S. bovis bacteremia.

Methods: From January 1992 to December 2001, 62 patients with S. bovis bacteremia were treated at National Taiwan University Hospital. Their demographic characteristics, clinical features, results of imaging studies, pathological findings, and laboratory data were retrospectively analyzed. Antimicrobial susceptibilities were determined using the agar dilution method and biotypes were determined using the API 20 Strep system.

Results: The majority of cases (76%) occurred during the 1996-1997 and 1999-2000 periods. Thirty five patients were male, and the mean age of the 62 patients was 61 years. Underlying diseases included malignancies (40%), cardiac diseases (27%), diabetes mellitus (24%), and liver cirrhosis (21%). Fifty two percent (n = 32) of patients presented with primary bacteremia and 24% (15) with definite or possible infective endocarditis. Thirteen percent (8) presented with hepatobiliary infections (acute cholecystitis and biliary tract infection). Ten patients (16%) had polymicrobial bacteremia. All of the concomitant pathogen(s) were Gram-negative rods, among which Escherichia coli predominated. The mortality rate on day 30 of illness was 21%. High Acute Physiology and Chronic Health Evaluation (APACHE) II score on the day of positive blood culture was associated with high mortality. Among the 19 patients (31%) who underwent colonoscopy, 9 (47%) had colonic lesions (tubular adenomas or carcinomas). Of the 26 patients (41%) who underwent echocardiography, 14 (54%) had vegetation in the valves. Of the 47 S. bovis isolates examined for biotypes, 37 (79%) were biotype II (29 of biotype II/2 and 8 of biotype II/1) and 10 (21%) were biotype I. The majority of isolates causing primary bacteremia (92%), hepatobiliary infections (100%) and primary bacterial peritonitis (100%) were biotype II, while 67% of isolates associated with infective endocarditis were biotype I. All isolates were susceptible to penicillin.

Conclusions: Infective endocarditis should be highly suspected in patients with bacteremia due to S. bovis biotype I. Investigations for intra-abdominal foci other than the colon should be undertaken in patients with bacteremia caused by S. bovis biotype II. Due to the increasing number of S. bovis bacteremia patients at the hospital and unknown origins of about 50% of bacteremia cases, the need for colonoscopy and echocardiography in each case and biotyping of each blood isolate should be emphasized.