Variation in risk for nosocomial chickenpox after inadvertent exposure

Inadvertent exposure to chickenpox in the healthcare setting results in time-consuming and expensive infection control management strategies. In households, secondary cases occur in up to 96% of susceptibles, but transmission risk after exposure in an occupational setting is less well defined. In this prospective cohort study of inadvertent exposures in a 180-bed paediatric hospital, the secondary transmission rate was 4.5% (4/89; 95% confidence interval 1.2, 11.1%). Fourteen index cases exposed 158 patients and 93 healthcare workers over a 36-month study period. Exposures occurred in inpatient and ambulatory settings, with patients, staff and siblings serving as index cases. Transmission only occurred when the index case and contacts were in the same room and not in a multi-room setting (12% v. 0%, Fisher exact test, P = 0.02). Occupational exposures present a lesser transmission risk than those in households. Definition of those exposure variables that increase risk of transmission in the occupational setting should be explored in future studies.