Objectives We have preciously documented that many individuals with acute mania have immune activation. However, the sources of immune activation have not been identified. We investigated whether individuals hospitalized with acute mania have evidence of bacterial infections as determined by the prescription of systemic antimicrobial agents.

Methods We assessed the recent prescription of systemic antimicrobial medications and the site of presumed bacterial infection in 234 individuals hospitalized for acute mania in either an inpatient unit or a day hospital. We also assessed individuals hospitalized for other psychiatric disorders (n=368) and controls (n=555). We employed logistic regression models to compare the rates of antibiotic prescription in individuals with the different diagnoses, employing demographic variables as covariates.

Results We found that individuals hospitalized with acute mania had a substantially increased rate of recent antimicrobial prescription, defined as exposure within three days of ascertainment (adjusted odds ratio=5.5, 95% confidence interval: 2.2–14.1, P<.0002). Overall, a total of 18 of the 234 (7.7%) individuals hospitalized for acute mania were prescribed antibiotics as opposed to seven of 555 (1.3%) controls. The prescription of antibiotics was associated with being on an inpatient unit as opposed to being in the day hospital, and having increased mania symptom severity but not with other clinical ratings, demographic variables, or psychiatric medications. Hospitalization for other psychiatric disorders was not associated with the recent prescription of antimicrobial medications. The urinary tract was the most common site of infection in women, while the respiratory tract and mucosal surfaces were the most common sites in men.