The epidemiology of children hospitalized with herpes zoster in Canada: Immunization Monitoring Program, Active (IMPACT), 1991-2005.

BACKGROUND

Varicella zoster virus causes varicella (chickenpox) and can reactivate to cause herpes zoster (HZ). In Canada, live attenuated varicella vaccine was recommended for routine use among healthy susceptible children age 1 year and older, in 1999. Varicella vaccine has had a profound impact on the incidence of varicella; however the impact on HZ remains uncertain.

METHODS

Surveillance for HZ admissions was conducted by the Immunization Monitoring Program, Active (IMPACT) surveillance network comprising 12 centers representing over 90% of pediatric tertiary care beds in Canada. Active surveillance for HZ was undertaken in 1991-1996 and reintroduced in 1999. A clinical diagnosis was accepted, with or without laboratory confirmation. For each case, a detailed case report form was completed.

RESULTS

In total, 648 children were admitted with HZ; 342 (52.8%) were boys and the mean age was 9.9 +/- 4.4 years. Five hundred seventy-seven (89.0%) were immunocompromised and 71 immunocompetent (10.8%). Five hundred seventy-one (88.1%) had a history of varicella zoster virus infection. Varicella vaccination was documented in 4 children before admission. Most (85.5%) presented with localized disease. Immunocompetent children were more likely than immunocompromised children to be hospitalized with ophthalmic disease (odds ratio 5.1, P < 0.001) or with at least 1 complication (odds ratio 3.0, P < 0.001). Only 1 death was attributable to HZ.

CONCLUSIONS

Immunocompromised children represented the overwhelming majority of IMPACT hospitalized cases. Complications directly resulting from HZ were common in immunocompetent children. As varicella vaccine use becomes more widespread, the IMPACT network will continue to play an important role in monitoring the changing epidemiology of HZ in children.