How airborne influenza may spread

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Washington, Nov 23 : Influenza usually spreads through direct contact and droplets, but a new study examines aerosol transmission as a possible way.

On April 4, 2008, seven inpatients in a Hong Kong hospital's general medical ward developed fever and respiratory symptoms. Eventually, nine inpatients exhibited influenza-like symptoms and tested positive for influenza A.

The cause of the outbreak was believed to be an influenza patient who received a form of non-invasive ventilation and was then moved to the intensive care unit after 16 hours.

During the time, he was located right beside the outflow jet of an air purifier, which created an unopposed air current across the ward.

"We showed that infectious aerosols generated by a respiratory device applied to an influenza patient might have been blown across the hospital ward by an imbalanced indoor airflow, causing a major nosocomial outbreak," said study author Nelson Lee of the Chinese University of Hong Kong.

"The spatial distribution of affected patients was highly consistent with an aerosol mode of transmission, as opposed to that expected from droplet transmission," he added.

"Suitable personal protective equipment, including the use of N95 respirators, will need to be considered when aerosol-generating procedures are performed on influenza patients," Lee added.

"Avoiding such procedures in open wards and improving ventilation design in health care facilities may also help to reduce the risk of nosocomial transmission of influenza."

The study is published in the current issue of Clinical Infectious Diseases.

http://www.newkerala.com/news/world/fullnews-90153.html

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Re: How airborne influenza may spread

Clinical Infectious Diseases 2010;51:1176?1183
? 2010 by the Infectious Diseases Society of America. All rights reserved.
1058-4838/2010/5110-0009$15.00
DOI: 10.1086/656743
MAJOR ARTICLE
Possible Role of Aerosol Transmission in a Hospital Outbreak of Influenza

Bonnie C. K. Wong,1

Nelson Lee,1

Yuguo Li,4

Paul K. S. Chan,2

Hong Qiu,3

Zhiwen Luo,4

Raymond W. M. Lai,2

Karry L. K. Ngai,2

David S. C. Hui,1

K. W. Choi,1 and

Ignatius T. S. Yu3

Departments of 1Medicine and Therapeutics, 2Microbiology, and 3Community and Family Medicine, The Chinese University of Hong Kong, and 4Department of Mechanical Engineering, University of Hong Kong, Hong Kong, China



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.

http://www.journals.uchicago.edu/doi/abs/10.1086/656743?prevSearch=%2528Nelson%2BLee%2529%2BAND%2B%255Bjournal%253A%2Bcid%255D&searchHistoryKey=