Controlled humidity could hit flu hard

is highlighting a recently published US study which it says backs over 60 years’ evidence that carefully controlling humidity in operating theatres and wards could significantly reduce transmission and survival of both the influenza virus, and potentially also other infection and virus-causing organisms. Jonathan Baillie reports.

Discussing with me the latest research on the impact of humidity on the influenza virus was Vapac’s national sales manager Dave Mortimer. Right from the start of our discussion, which took place in an office next to the large factory in Edenbridge, Kent where the company assembles its range of electrode boiler and resistive heating humidifiers for healthcare, educational, industrial, retail, and office applications in both the UK and overseas, he made clear his own strong belief in the scientific arguments for greater use of hospital humidification in combating the spread of both influenza, and possibly (depending on the results of several ongoing studies), other bacteria and viruses. Indeed evidence of the impact of, for instance, maintaining relative humidity at between 40 and 60% on the viability and survival of several strains of “flu” had, he told me, been welldocumented since the 1940s. Two key recent developments had, however, re-focused debate on the issue – guidance in the latest Healthcare Technical Memorandum covering heating and ventilation of healthcare premises (HTM 03-01, published in November 2008) that appears to indicate a change in Department of Health thinking on the need to install humidifiers in some operating theatres, and publication of a US study that focuses on the potential effect on influenza survival and transmission of both relative (RH) and, more particularly, absolute humidity (AH) levels. The US paper, (Absolute humidity modulates influenza survival, transmission, and seasonality, Sharman J., Kohn M.), was authored by Professor Jeffrey Shaman, assistant professor at the College of Oceanic and Atmospheric Studies at Oregon State University in the US, and Melvin Kohn of the Public Health Division at the Oregon Department of Health Services. One of its key conclusions is that, “while for certain organisms relative humidity may indeed affect biological response” (endorsing the belief that maintaining RH between set parameters in hospitals may well reduce influenza spread), the absolute humidity (AH), i.e. the actual water vapour content of the air irrespective of temperature, “can be of greater biological significance for many organisms”. The study goes on to suggest that absolute humidity is, in fact, the “defining factor”, and can “greatly reduce both the viability of the flu virus, and the transmission of influenza”.

Further research needed