Risk Factors for Viridans Group Streptococcal Bacteremia in Neutropenic and Non-neutropenic Patients: A Single Center Case-Case-Control Study

Background. Viridans group streptococcal (VGS) bacteremia is common among neutropenic patients. Although VGS bacteremia occurs in non-neutropenic patients, risk factors are not well established. We conducted a case-case-control study to identify risk factors for VGS among neutropenic and non-neutropenic patients. Methods. Patients with VGS bacteremia between January 2009 and December 2014 in our 200-bed clinical research hospital were identified using microbiology records. Neutropenic and non-neutropenic patients at the time of positive culture were matched 1:1 to controls on the basis of neutrophil count (ANC), ward, and length of stay. We extracted demographic, laboratory, medication, and other clinical data from chart reviews. Data were analyzed using McNemar's test, Wilcoxon signed-rank test, and conditional logistic regression modeling. Results. Among 101 patients, 63 were neutropenic and 38 non-neutropenic at the time of VGS bacteremia. In multivariable analysis of neutropenic patients, only lower ANC predicted VGS bacteremia (odds ratio [OR], 0.16; 95% confidence interval [CI], 0.05-0.59; P = 0.006). Recent use of vancomycin was protective (OR, 0.23; 95% CI, 0.07-0.73; P = 0.013). No clinical factors were associated with VGS in the non-neutropenic cases. Conclusions. Only lower ANC nadir increased the risk for VGS bacteremia in the neutropenic group, and vancomycin was protective. Other previously described factors (chemotherapy, radiation, oral conditions) related to neutropenia were not independently associated with VGS bacteremia. No tested clinical factors predicted infection in the non-neutropenic group. Our results suggest that VGS bacteremia should be anticipated when making antimicrobial choices in profoundly neutropenic patients, and merit further exploration in non-neutropenic patients.