Journal Article

Possible Role of Aerosol Transmission in a Hospital Outbreak of Influenza

Bonnie C. K. Wong, Nelson Lee, Yuguo Li, Paul K. S. Chan, Hong Qiu, Zhiwen Luo, Raymond W. M. Lai, Karry L. K. Ngai, David S. C. Hui, K. W. Choi and Ignatius T. S. Yu

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 51, issue 10, pages 1176-1183
Published in print November 2010 | ISSN: 1058-4838
Published online November 2010 | e-ISSN: 1537-6591 | DOI: http://dx.doi.org/10.1086/656743
Possible Role of Aerosol Transmission in a Hospital Outbreak of Influenza

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Background. We examined the role of aerosol transmission of influenza in an acute ward setting.

Methods. We investigated a seasonal influenza A outbreak that occurred in our general medical ward (with open bay ward layout) in 2008. Clinical and epidemiological information was collected in real time during the outbreak. Spatiotemporal analysis was performed to estimate the infection risk among patients. Airflow measurements were conducted, and concentrations of hypothetical virus-laden aerosols at different ward locations were estimated using computational fluid dynamics modeling.

Results. Nine inpatients were infected with an identical strain of influenza A/H3N2 virus. With reference to the index patient's location, the attack rate was 20.0% and 22.2% in the “same” and “adjacent” bays, respectively, but 0% in the “distant” bay (P=.04). Temporally, the risk of being infected was highest on the day when noninvasive ventilation was used in the index patient; multivariate logistic regression revealed an odds ratio of 14.9 (95% confidence interval, 1.7–131.3; P=.015). A simultaneous, directional indoor airflow blown from the “same” bay toward the “adjacent” bay was found; it was inadvertently created by an unopposed air jet from a separate air purifier placed next to the index patient's bed. Computational fluid dynamics modeling revealed that the dispersal pattern of aerosols originated from the index patient coincided with the bed locations of affected patients.

Conclusions. Our findings suggest a possible role of aerosol transmission of influenza in an acute ward setting. Source and engineering controls, such as avoiding aerosol generation and improving ventilation design, may warrant consideration to prevent nosocomial outbreaks.

Journal Article.  4546 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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