BackgroundThe spread of influenza and highly pathogenic avian influenza (H5N1) presents a significant threat to human health. Avian influenza outbreaks in downwind areas of Asian dust storms (ADS) suggest that viruses might be transported by dust storms.ObjectivesWe developed a technique to measure ambient influenza and avian influenza viruses. We then used this technique to measure concentrations of these viruses on ADS days and background days, and to assess the relationships between ambient influenza and avian influenza viruses, and air pollutants.MethodsA high-volume air sampler was used in parallel with a filter cassette to evaluate spiked samples and unspiked samples. Then, air samples were monitored during ADS seasons using a filter cassette coupled with a real-time quantitative polymerase chain reaction (qPCR) assay. Air samples were monitored during ADS season (1 January to 31 May 2006).ResultsWe successfully quantified ambient influenza virus using the filtration/real-time qPCR method during ADS days and background days. To our knowledge, this is the first report describing the concentration of influenza virus in ambient air. In both the spiked and unspiked samples, the concentration of influenza virus sampled using the filter cassette was higher than that using the high-volume sampler. The concentration of ambient influenza A virus was significantly higher during the ADS days than during the background days.ConclusionsOur data imply the possibility of long-range transport of influenza virus.

Influenza viruses cause pandemics in humans. The aim of this study was therefore to evaluate filter/real-time qPCR to quickly and accurately determine and quantify the airborne influenza and avian influenza virus. In this study, the sampling stress of filtration to influenza virus and the storage effects for both the virus and extracted RNA were evaluated in the laboratory. Then, the collection efficiencies of open-face and closed-face filter cassettes were compared in a wet poultry market. From July 8 to August 19, 2006, a total of 36 air samples were quantified by filter/real-time qPCR.The recovery rate of the virus on a filter stored at 4• C reached 0.94 after 3-day storage, whereas the RNA stored at -80• C was 100% after 3-month storage. In terms of collection efficiency, the closed-face filter cassette was superior to the open-face filter cassette in the field study. In the wet poultry market, it was revealed that both the positive rate and concentration of influenza A virus in the chicken pen were higher than that in the duck pen, possibly due to differences in ventilation type, climate factors, and avian characteristics. To our knowledge, this is the first report describing the quantification of airborne influenza virus in field samples. This quantitative technique should provide more insight into influenza/avian influenza virus transmissibility and epidemiology of influenza/avian influenza, as well as infection control.