Air handling units could be used to study airborne microorganisms such as anthrax, according to engineers in the US.

Air handling units (AHUs) are already installed in most modern buildings, and their filters routinely collect viruses and bacteria from the air (bioaerosols). James Farnsworth of TSI Incorporated, working with scientists from the University of Minnesota, argues that these filters could be removed and the amount of each species measured. The filters trap a relatively small amount of potential pathogens, and collecting the samples would cause no inconvenience to the buildings' occupants.

The team believe that although this type of sampling could not provide early warning of a biological attack, it could determine the background level of pathogens and bacteria similar to them. This would reduce the chance of false positive results in biosensors. Rather than studying pathogens such as anthrax and smallpox, the team used safer surrogate bacteria and viruses.

To prove their method, the team successfully cultured bacteria collected on typical AHU filters. However, they found that the viruses died within a few hours of settling on the filters, but suggest that they could be identified by the polymerase chain reaction, a method that involves replicating small amounts of DNA that can then be used to identify the microorganisms.

Clive Beggs of the University of Bradford, UK, was positive about the technique, saying that it was 'applicable for bacterial and fungal species'. Bioaerosol expert W David Griffiths of Airborne Matters, UK, reflected that 'it may be more efficient and less costly to use bioaerosol samplers in the room'.

Farnsworth is undeterred and believes that 'high volume sampling using AHUs could be a wonderful tool. The data generated from this research will be useful to the developers of biodetectors.'

Wendy Crocker