Factors associated with complicated viridans group streptococcal bacteremia in adults: impact of oral health

Viridans group streptococci can cause invasive disease. However, predictors of complicated infection in adult viridans group streptococcal bacteremia, including the role of oral sources, remain unclear. This single-center retrospective cohort study included adults (≥ 18 years) with viridans group streptococci isolated from blood cultures at Saga University Hospital, Japan, between September 2014 and June 2025. Patients with polymicrobial bacteremia, cardiopulmonary arrest on arrival, contamination, or interhospital transfer were excluded. Complicated bacteremia was defined as infective endocarditis or metastatic pyogenic infection with isolation of viridans group streptococci from a sterile site other than blood. Independent factors were identified using multivariable logistic regression. Among 164 patients, 54 (33%) developed complicated infection, most commonly infective endocarditis (41%), intra-abdominal abscess/peritonitis (22%), and deep neck infection (15%). Median age did not differ between complicated and uncomplicated cases (68 vs. 70 years, p = 0.81). White blood cell counts ( p < 0.0001) and C-reactive protein levels ( p = 0.0005) were higher in complicated cases. In-hospital mortality was 0% in complicated versus 5% in uncomplicated cases ( p = 0.18). On multivariable analysis, factors independently associated with complicated infection were community acquisition (adjusted odds ratio [aOR], 4.89; 95% confidence interval [CI], 2.31–10.8), odontogenic source (aOR, 3.07; 95%CI, 1.44–6.70), and Streptococcus anginosus group bacteremia (aOR, 2.87; 95%CI, 1.33–6.47). One-third of adults with viridans group streptococcal bacteremia developed complicated infection. Community acquisition and S. anginosus group infection may raise suspicion for an odontogenic source, supporting early imaging, prompt dental evaluation, and timely source control.