BACKGROUND: In May and August 2016, Rhode Island Department of Health (RIDOH) responded to two outbreaks of varicella at two Rhode Island prisons (A and B). Each outbreak was initiated by a case of orofacial herpes zoster who had not been placed in isolation.
METHODS: In Prison A, all exposed inmates received one dose of post-exposure varicella vaccine, and were concurrently serologically assessed for IgG immunity. Seronegative inmates received a second dose of vaccine 41 days after the first dose. In Prison B, serologic screening was performed prior to vaccination, and only seronegative inmates were vaccinated. Exposed staff in both prisons were offered vaccine. RIDOH used Pearson chi-square analysis, Fisher’s exact test, and pooled t-tests to investigate associations between varicella immunity and age, race, birth before 1980, and self-reported prior varicella infection.
RESULTS: RIDOH confirmed 5 cases of varicella in Prison A and 3 cases in Prison B. Cases ranged in age from 29-45 years, and all developed 50-249 lesions. None reported immunocompromising conditions or prior varicella infection. In Prison A, 432 inmates were exposed to varicella and 88.9% were IgG positive. Seropositive inmates were significantly older than seronegative inmates (mean 38.7 years vs 31.8 years, p=0.0003). Birth before 1980 was also associated with immunity. Seropositive inmates were more likely to self-report prior varicella disease than seronegative inmates (68% vs. 29%; p<0.0001). In Prison B, 46 inmates were exposed to varicella; 89.1% were IgG positive. Only 5 inmates required vaccination. There was no association between varicella immunity and age, race, or birth before 1980.
CONCLUSIONS: In each outbreak, a swift, coordinated response prevented further spread of varicella. In Prison A, due to the short timeframe for post-exposure prophylaxis, 374 immune inmates received vaccine before serologic results were available. In Prison B, serologic screening was conducted prior to post-exposure vaccination, and only 5 doses of varicella were needed. There is limited literature detailing varicella immunity among incarcerated populations. Eighty-nine percent (89%) of exposed inmates in both prisons were found to be immune to varicella. Serologic screening in Prison B reduced expenditure of time, money and staffing resources, as well as unnecessary vaccine administration. The window for post-exposure varicella vaccination is short, and there is not always time to wait for serology results before administering vaccine during an outbreak. Serologic screening upon intake into the correctional system can avert cost and excess vaccination in the event of a varicella outbreak.