The 35-year-old father of a 5-month-old baby presented with a five-day history of painful herpes zoster and a number of questions: Is his child, who is no longer being breastfed, at risk for chickenpox? Can the virus be transmitted by swimming in the family pool? What is the actual risk for this infant? What mode of transmission is most likely? What approach to prevention would be most effective?
—Daren Rauch, MD, Clinton, Ill.

Any individual who has not had varicella or has not been vaccinated is at risk of developing this condition upon exposure to varicella-zoster virus (VZV). Varicella, itself, is common and highly contagious, and it affects nearly all susceptible children before adolescence. Children who are susceptible, however, rarely acquire the disease through contact with adults who have zoster.

Zoster lesions contain high concentrations of VZV that can be spread, either by airborne transmission or direct contact, and cause primary varicella in exposed susceptible persons. Localized zoster is contagious only between the time the rash erupts and the lesions crust. Zoster is less contagious than varicella. In one study of VZV transmission from zoster, varicella occurred among 15.5% of susceptible household contacts. In contrast, following household exposure to varicella, a more recent study demonstrated VZV transmission among 71.5% of susceptible contacts. Individuals with localized zoster are less likely to transmit VZV to susceptible persons in household or occupational settings if their lesions are covered (MMWR Recomm Rep. 2008;67[RR-5]:1-30).

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I am familiar with the case of a 9-month-old infant who was exposed to an adult with zoster. The recommendation for treatment was to administer the varicella vaccine immediately following the exposure. The varicella vaccine was given again, per standard recommendations, at 1 year of age. The infant did not develop varicella.
—Jeffrey M. Weinberg, MD