An Outbreak of Airborne Nosocomial Varicella

An outbreak of nosocomial varicella was traced to airborne spread from an immunocompromised child hospitalized from Nov 11-19, 1980. Seventy potentially susceptible children were hospitalized on the ward during that period. Although the index patient remained in strict room isolation throughout his hospital stay, eight of these patients contracted varicella. The afternoon of November 12 was the period of highest risk for acquiring varicella. Eight of 36 patients (22%) present that afternoon, compared to none of 34 patients not present that afternoon, acquired the infection. A patient's risk of contracting varicella was significantly related to how near he/she came to the index patient's room that afternoon. Airflow studies, using the tracer gas, sulfur hexafluoride (SF6), demonstrated that patient rooms on this ward were at positive pressure with respect to the corridor. Despite isolation procedures, SF6 released in the index patient's room achieved concentrations in the corridor as high as 10% of those inside the room. Airborne spread of varicella has rarely been reported, but it may be a common mode of transmission in hospitals. We suggest that patients hospitalized with varicella be placed in strict isolation in negative-pressure rooms to reduce the risk of nosocomial transmission.