Measles, mumps, rubella, and varicella seroprevalence in health care workers: A cross-sectional study from Tan Tock Seng Hospital and the National Centre for Infectious Diseases, Singapore

OBJECTIVES: We assessed measles, mumps, rubella (MMR) and varicella seroprevalence and factors associated with seropositivity among our institutions' health care workers (HCWs). METHODS: This cross-sectional enzyme-linked immunosorbent assay (ELISA) seroprevalence study of HCWs' residual sera from 2020 assessed factors associated with seropositivity using logistic regression and tested performance characteristics of an "immunity" criterion (composite of past vaccination and serology results) against seropositivity. Measles non-seropositive sera were re-tested with plaque neutralization reduction tests (PRNTs). RESULTS: A total of 284 HCWs were included. MMR and varicella ELISA seropositivity were 74.7% (95% confidence interval 69.2-79.6), 82.0% (77.1-86.3), 97.9% (95.5-99.2), and 94.0% (90.6-96.5), respectively. Measles (ELISA + PRNT) seropositivity was 100.0% (98.7-100.0). Mumps seropositivity was inversely associated with Singapore citizenship/permanent residency (adjusted odds ratio [aOR]: 0.32 [0.12-0.74]). Varicella seropositivity was associated with past seropositivity and completed vaccination (aOR: 20.39 [2.79-428.71] and 0.10 [0.01-0.56], respectively). The positive and negative predictive values of "immunity" were 100.0%, 0.0% (measles [ELISA + PRNT]); 82.0%, 16.7% (mumps); 98.1%, 5.6% (rubella); and 94.5%, 10.0% (varicella), respectively. CONCLUSIONS: Participants had high measles, rubella, and varicella seroprevalence but not mumps. The immunity criterion was unreliable for mumps. Vaccinating HCWs with a third MMR dose could be considered in mumps outbreaks. Infection prevention and control measures remain important.