ABSTRACT
Introduction: Varicella is an acute disease with significant morbidity. However, there is little knowledge on the seroepidemiology of the disease in Singapore. The objective of this study was to assess the seroprevalence of varicella zoster virus (VZV) antibodies in military recruits in Singapore and to ascertain the predictive value of a self-reported history of varicella. The latter is a possible proxy for seroprevalence, and may be used to provide efficient identification of candidates for vaccination. Materials and Methods: From September 2000 to October 2005, 2189 servicemen were selected during their pre-enlistment medical check-up. Blood samples were obtained to determine the varicella IgG levels via enzyme-linked immunosorbent assay (ELISA). Information about the participant’s race, history of varicella and vaccination, and other clinical variables were obtained through a questionnaire. Results: The overall prevalence of VZV sero\-positivity in military recruits was 76.0% (75.8% in the 16 years to 20 years age group). For the reported history, 73.7% of Chinese participants, 73.0% of Malays, and 63.6% of Indians reported having had varicella infection and/or vaccination. Overall, the sensitivity, specificity, positive and negative predictive values of a self-reported history of varicella for serologically confirmed immunity were 87.2%, 83.2%, 94.3% and 67.1% respectively. Conclusions: The prevalence of VZV antibodies in pre-enlistees to the Singapore Armed Forces (SAF) is high. Incidence of varicella in the SAF is on the wane, indicating an increase in herd immunity against VZV. A recalled history of varicella infection was also a good predictor of serological immunity and may be used for selection for vaccination.
Varicella is an acute, self-limiting exanthematous disease characterised by a prolonged period of morbidity lasting up to 2 weeks.1 Despite being mostly benign in healthy individuals, varicella infection can result in substantial loss of productivity. A study by Lee et al2 estimated that the disease costs Singapore US$11.8 million per annum, with the largest proportion attributable to days lost from work. Despite an overall decline in the national incidence of varicella since 1996, the average annual incidence of the disease in Singapore remains substantive, with 506 cases per 100,000 individuals3 with occasional outbreaks. In 2004, reported cases of varicella increased by 32% compared with 2003, with 206 institutional outbreaks island-wide. Within the Singapore Armed Forces (SAF), varicella rates have decreased over the years but outbreaks continue to contribute substantially to workdays lost. Knowledge of the seroprevalence of varicella within the SAF is important in developing vaccination strategies and other public health measures to minimise the healthcare and economic impact.
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