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

Background 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. Methods This single-center retrospective cohort study was conducted at Saga University Hospital, Japan, among adults (≥ 18 years) with viridans group streptococci isolated from blood cultures 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. Multivariable logistic regression was used to identify independent risk factors. Results 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 was similar 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 rate was 0% in complicated cases and 5% in uncomplicated cases (p = 0.18). In multivariable analysis, independent predictors for 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). Conclusions One-third of adults with viridans group streptococcal bacteremia developed complicated infection. Community acquisition, odontogenic origin, and S. anginosus group etiology may help prioritize early imaging, dental evaluation, and timely source control.