Clinical Significance of Viridans Streptococcal Bacteremia

Cho, Eun Hae; Lee, Nam Yong

Abstract

BACKGROUND
Viridans streptococci, a diverse group of streptococcal species is present in the oral flora of all humans, and clinical isolation of these organisms could be misinterpreted as contamination. The purposes of this study were to ascertain the clinical significance of viridans streptococcal bacteremia and to determine the epidemiological, clinical, and microbiological features. METHODS: All cases of viridans streptococcal bacteremia in the period from January 1998 to December 2002 were reviewed. Bacterial identification was done with the Vitek system, and antimicrobial susceptibility tests for penicillin, cefotaxime, chloramphenicol, clindamycin, and erythromycin by the disk diffusion method or E-test were carried out. RESULTS: Of 154 cases of viridans streptococcal bacteremia, 56 cases were identified to the species level such as S. salivarius (19), S. mitis (16), S. intermedius (7), S. sanguis (7), S. uberis (3), S. oralis (2), S. bovis (1), and S. mutans (1). The most frequent diagnostic category was infectious diseases (54), followed by solid organ tumors (45), hematologic malignancies (29), and liver diseases (8). Seven patients (4.5%) had subacute endocarditis and all of them had underlying heart disease. Seventy six (49.3%) patients showed positive blood culture from two or more blood samples. Thirty three (21.4%) patients had an absolute neutrophil count of less than 500 cells/ L. Thirty four cases of bacteremia were polymicrobial (22%). When the diagnosis of viridans streptococcal bacteremia was established by the presence of two or more positive blood cultures or presence of neutropenia or signs of sepsis, 29.9% was interpreted as contamination. Two patients died of septic shock caused by viridans streptococcal infection alone. Sixty-eight percent of isolates were susceptible to penicillin. CONCLUSIONS: About 70% of viridans streptococcal bacteremia was clinically significant. Most viridans streptococcal bacteremia was found in patients with cancer or neutropenia and these infections were associated with limited morbidity.