Source, Engineering Controls Can Help Prevent Aerosol Transmission of Influenza

Researchers from the Chinese University of Hong Kong, and from the University of Hong Kong examined the role of aerosol transmission of influenza in an acute ward setting and suggest that source and engineering controls, may warrant consideration to prevent hospital-acquired outbreaks. Their research was published in the November issue of Clinical Infectious Diseases.

They investigated a seasonal influenza A outbreak that occurred in the general medical ward in 2008. The researchers collected clinical and epidemiological information during the outbreak 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.

Wong, et al. (2010) report that nine inpatients were infected with an identical strain of influenza A/H3N2 virus. With reference to the index patients location, the attack rate was 20.0 percent and 22.2 percent in the "same" and "adjacent" bays, respectively, but 0 percent in the "distant" bay (P=.04). The researchers reportt hat 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 percent confidence interval, 1.7131.3; 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 patients 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.

Reference: Wong BCK, Lee N, Li Y, Chan PKS, Qiu H, Luo Z, Lai RWM, Ngai KLK, Hui DSC, Choi KW and Yu ITS. Possible Role of Aerosol Transmission in a Hospital Outbreak of Influenza. Clinical Infectious Diseases. 2010;51:1176-1183.