Laboratory confirmation of varicella outbreaks is recommended but can be challenging in practice. Even if seen by a health care provider, cases are most often clinically diagnosed. We devised an alternative method for obtaining specimens for laboratory confirmation, using collections kits distributed to parents of cases through schools and childcare centers.
METHODS:
Between September 2012 and December 2015, the Minnesota Department of Health (MDH) assembled kits for parents to collect specimens on their symptomatic children at home during school and child care outbreaks. Kits contained 2 glass slides for gentle removal of loose scabs and crusts, a buccal cell collection swab, and a combined instruction and consent document. A gift card incentive was provided. Kits were initially sent to the school nurse, health aide, or other staff for distribution to interested parents who reported that their children had chickenpox. Participating parents either dropped off specimens at the school or sent them directly to MDH, using a provided mailer. Specimens were tested for varicella-zoster virus (VZV) DNA by polymerase chain reaction (PCR) at either the CDC National VZV Laboratory or the MDH Public Health Laboratory.
RESULTS:
Specimens from 22 cases related to suspected outbreaks were received from 10 schools and 2 childcare centers. Buccal swabs were received from 21 (95.5%) cases. Dermal specimens on slides were received from 18 (81.8%) cases; 17 of these were identified as crusts or scabs and one as a vesicular scraping. VZV DNA was detected in 71.4% of buccal swabs and in 94.1% of dermal specimens. When both specimens were submitted, discordant results were obtained in 3 (17.6%) cases; in all instances, the dermal specimen results were positive and the buccal swab results were negative or indeterminate. However, two cases were able to be laboratory-confirmed even though only buccal swabs were submitted for testing. Four cases had been vaccinated for varicella; VZV DNA was detected in specimens from 2 cases (50%).
CONCLUSIONS:
In our limited sample, crusts and scabs were more often positive for VZV DNA than buccal swabs, but providing both collection options enabled us to confirm more cases. Although collection of specimens by a health care provider under controlled conditions is preferable, our method was highly successful in confirming suspected outbreaks.