BACKGROUND: Since two doses of varicella vaccine (VV) became part of the routine childhood vaccination schedule in the U.S. in 2006, varicella incidence, hospitalizations and deaths have further declined. Although varicella in adults can be more severe with complications like pneumonia and encephalitis, catch-up VV rates among susceptible adults are considered to be low. Individuals in congregate living settings are at a higher risk for varicella infection because of close proximity to others. We describe varicella clusters (>3 cases in a 3-week period) and outbreaks (>5 cases in a 3-week period) in residential facilities for adults in Philadelphia.
METHODS: During 2011-2015, the Philadelphia Department of Public Health (PDPH) used passive surveillance to identify varicella clusters and outbreaks in residential facilities. We examined confirmed adult varicella cases associated with residential facility clusters and outbreaks by disease severity and varicella-zoster virus (VZV) immunity status, as well as control measures implemented.
RESULTS: Two clusters and two outbreaks were reported (1 substance abuse treatment facility and 3 prisons) that involved 3-9 varicella cases. Index cases were 2 herpes zoster cases and 2 unvaccinated varicella cases. The median duration of the clusters and outbreaks was 25 days (range: 15-34). Of the cluster- and outbreak-related varicella cases, 17 were adults aged 22-47 years. Of those, 13 (76%) reported rashes with ≥50 lesions, 2 (12%) had confirmatory laboratory testing performed and none were hospitalized or fatal. Sixteen (94%) were unvaccinated or had an unknown VV history and 1 (6%) reported a history of VV. Fifteen (88%) had no reported disease history or had an unknown disease history and 2 (12%) reported a previous disease history. During each cluster and outbreak, VZV immunity testing of contacts was performed. The median number of asymptomatic adult contacts tested for VZV immunity was 82 (range: 8-317). Overall, 43 (9%) contacts were susceptible to VZV. Of those, 36 (84%) were subsequently isolated for one incubation period (21 days). Post-exposure VV was provided to 21 susceptible contacts as an outbreak control measure. For one incubation period, admissions were restricted to those with documented evidence of VZV immunity.
CONCLUSIONS: More stringent criteria for VZV immunity as with healthcare workers, pregnant women, and immunocompromised individuals may be beneficial for adults in residential facilities. Providing VZV immunity testing and VV to adults lacking immunity upon admission could prevent VZV transmission in close-contact congregate living situations and reduce disruptions to facility operations due to varicella outbreak management.