A Varicella Outbreak in An Adult Residential Care Facility

Background:  Because most adults had varicella during childhood, birth before 1980 is generally considered evidence of immunity. Varicella outbreaks among adults are rare. During December 2008–January 2009, the Connecticut Department of Public Health and Centers for Disease Control and Prevention investigated a varicella outbreak in a residential facility for adults with mental retardation. 

Objectives: Describe the outbreak, determine risk factors, and identify the origin of the outbreak.

Methods: A varicella case was defined as a generalized maculopapular rash (with or without vesicles without other apparent cause) that developed after November 1, 2008 in a resident of the facility.  Sera from cases were tested for specific immunoglobulins and lesions were tested by polymerase chain reaction (PCR). Information on all residents was abstracted from facility medical charts and admission histories using a standard form and by interviews of caregivers.

Results: Eleven cases were identified among 70 residents (attack rate 15.7%). The median age was 39 years (range 32–49 years). Cases were younger at first institutionalization than non-cases (9.5 vs. 15.0 years, p<0.01). A possible herpes zoster case retrospectively identified in the roommate of the first varicella case is thought to be the source of the outbreak.  The possible index case’s lesions had not been kept covered. Ultimately the outbreak was curtailed by vaccinating 55 non-case residents.

Conclusions: This outbreak exemplifies the potential for at-risk pockets of varicella-susceptible adults, especially among those institutionalized from a young age, the importance of appropriate management of herpes zoster to prevent transmission, and the challenges of controlling an outbreak in this type of setting. Varicella vaccination status or evidence of immunity should be verified for all adults residing in similar settings. Birth in the United States before 1980 may not be predictive of immunity to varicella among adults who have been institutionalized since childhood.