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An outbreak of airborne nosocomial varicella
Insights
Airborne transmission of varicella (chickenpox) occurred in a hospital ward despite isolation. Patients closer to the infected individual were at higher risk, highlighting the need for negative-pressure rooms for varicella patients.
Area of Science:
- Infectious Diseases
- Hospital Epidemiology
- Infection Control
Background:
- Nosocomial varicella outbreaks pose a significant risk in healthcare settings.
- Standard isolation procedures may not be sufficient to prevent airborne transmission of varicella.
Purpose of the Study:
- To investigate the transmission dynamics of a nosocomial varicella outbreak.
- To identify risk factors associated with varicella acquisition in a hospital ward.
- To evaluate the effectiveness of isolation measures and airflow dynamics in preventing varicella spread.
Main Methods:
- Retrospective cohort study tracing an outbreak of varicella.
- Analysis of patient proximity to the index case.
- Airflow studies using sulfur hexafluoride (SF6) tracer gas to assess room pressurization and airborne particle movement.
Main Results:
- Eight of 70 potentially susceptible children contracted varicella despite isolation of the index patient.
- The highest risk of infection occurred on November 12, with 22% of patients present that afternoon acquiring varicella.
- Patient proximity to the index patient's room was significantly related to infection risk.
- Airflow studies revealed positive room pressure, allowing airborne contaminants to spread into the corridor.
Conclusions:
- Airborne spread of varicella can occur in hospitals, even with isolation.
- Hospital ward airflow dynamics contributed to the transmission.
- Strict isolation in negative-pressure rooms is recommended for hospitalized varicella patients to prevent nosocomial transmission.
Abstract:
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.