Objective: Our study examines risk factors for severe varicella in an outbreak among Mexican-born adults, and it compares susceptibility to infection and reliability of self-reported varicella history for these individuals with that for adults born in the United States in the outbreak locale, which may guide vaccination strategies.
Methods: We interviewed case patients and non-case persons in the affected apartment complex and workplace, assessed disease history and susceptibility by testing for varicella-zoster virus immunoglobulin G antibodies, and reviewed the clinical data of case patients.
Results: Five of 18 case patients had serious complications for which they sought medical care; 1 was hospitalized for pneumonia, and 1 was hospitalized for Guillain-Barré syndrome. Only intense exposure (e.g., sharing a bed) was marginally associated with severe disease (P=.08). In the workplace, varicella susceptibility was higher among Mexican-born workers (20%) than among workers born in the United States (3%) (adjusted prevalence odds ratio, 5.4; 95% confidence interval, 2.3-14.8). Mexican-born persons had the highest positive predictive value of self-reported disease (100%) in predicting immunity, and those born in the United States had the lowest negative predictive value of self-reported history (10%) in predicting susceptibility.
Conclusions: Varicella is a more serious disease among adults than among children, and Mexican-born adults living in the United States might have a higher risk of acquiring varicella than US-born adults. Varicella outbreaks involving adults should be prioritized for control efforts. Outbreaks can be prevented by vaccinating susceptible adults.