Transmission of Varicella Zoster Virus from Herpes Zoster Cases in School and Childcare Settings

Background:
Although less contagious than varicella, herpes zoster (HZ) is also responsible for spread of varicella zoster virus (VZV). VZV transmission may occur through direct contact with or inhalation of aerosols from localized HZ rashes. Under current recommendations, immunocompetent persons with HZ can remain in school/childcare settings as long as their lesions can be completely covered.

Objectives:
To describe VZV transmission that may have resulted from HZ cases in school and childcare settings during the post-vaccine-licensure era.

Methods:
We conducted a retrospective analysis of HZ and varicella surveillance data from schools/childcare facilities in Philadelphia during September 2003-August 2008. An HZ index case was defined as a case of HZ reported from a facility at least 6 weeks after and 10 days (minimum incubation period) before other reports of varicella from the same facility. Secondary varicella cases were reports of varicella occurring ≥10 days after an HZ index case. Outbreaks were ≥5 varicella cases occurring within a 3-week period at the same facility.

Results:
During September 2003-August 2008, 236 HZ cases were reported in school/childcare settings, ranging from 24 to 60 HZ cases per academic year. Forty-three HZ cases (18%) were index HZ cases and were followed by 109 secondary varicella cases. Most HZ index cases (80%) were aged <20 years. While the majority (78%) were linked to 1 or 2 secondary varicella cases, 7 were followed by varicella outbreaks that involved between 5 and 33 secondary cases.

Conclusions:
Our findings suggest that VZV transmission in school/childcare settings from individuals with HZ may not be uncommon and could contribute to varicella morbidity in the post-vaccine-licensure era. More research is needed on risk factors for VZV transmission from persons with HZ in school and childcare settings to determine if current recommendations are adequate for preventing transmission in these settings.