# 4893
The `conventional wisdom’ is that human influenza viruses are pretty fragile, and are unlikely to survive in the environment (outside of a host) for more than a few hours.
In fact, the CDC’s Fact Sheet on Preventing Seasonal Flu gives the following advice:
How long can human influenza viruses remain viable on inanimate items (such as books and doorknobs)?
Studies have shown that human influenza viruses generally can survive on surfaces for between 2 and 8 hours.
Of course . . . there are exceptions. Certain environmental conditions that promote longer survival.
In 2008 we saw a study from the Central Laboratory of Virology in Geneva, Switzerland showing that seasonal influenza viruses could survive on Swiss banknotes (when encapsulated in mucus) for up to 17 days.
Survival of influenza virus on banknotes.
Thomas Y, Vogel G, Wunderli W, Suter P, Witschi M, Koch D, Tapparel C, Kaiser L.
Abstract (Excerpt)
Influenza A viruses tested by cell culture survived up to 3 days when they were inoculated at high concentrations. The same inoculum in the presence of respiratory mucus showed a striking increase in survival time (up to 17 days).
Similarly, B/Hong Kong/335/2001 virus was still infectious after 1 day when it was mixed with respiratory mucus. When nasopharyngeal secretions of naturally infected children were used, influenza virus survived for at least 48 h in one-third of the cases.
Temperature, humidity, sunlight (UV rays) and the type of environment (hard surface, porous material, water, etc) all play a role in how long a virus might survive outside of a living host.
As you might imagine, given the difficulty that countries like Indonesia, Egypt, and Vietnam have had in eradicating the H5N1 virus, research in its ability to survive in the environment is of great interest.
Last month (see Of Ducks, And Feathers, And H5N1) we saw a study that determined that the H5N1 virus may persist on the dropped feathers from infected ducks and that they may spread the virus to the environment. You can follow the link below to read the abstract.
Applied and Environmental Microbiology, August 2010, p. 5496-5499, Vol. 76, No. 16
0099-2240/10/$12.00+0 doi:10.1128/AEM.00563-10Persistence of Avian Influenza Virus (H5N1) in Feathers Detached from Bodies of Infected Domestic Ducks
Yu Yamamoto, Kikuyasu Nakamura, Manabu Yamada, and Masaji Mase
The surprising part of this study is how long these feathers retained some degree of viral contamination at various temperatures.
At 4°C (39F) the virus was detectable for 160 days, while at the higher temperature 20°C (68F), the virus was detected for 15 days.
Today, a new study that appears in Environmental Science and Technology titled:
Environmental Persistence of a Highly Pathogenic Avian Influenza (H5N1) Virus
Joseph P. Wood, Young W. Choi, Daniel J. Chappie, James V. Rogers, and Jonathan Z. Kaye
DOI: 10.1021/es1016153
Publication Date (Web): September 3, 2010
Copyright © 2010 American Chemical Society
Here researchers conducted tests on four inanimate materials (glass, wood, galvanized metal, and top soil) to determine how long – and under what environmental conditions – the virus could survive.
They adjusted factors such as temperature, relative humidity, and simulated sunlight and checked the samples over a period of 13 days.
The virus was most persistent at lower temperatures, and on surfaces such as glass and steel. Their conclusion?: at these conditions, the virus would be expected to persist appreciably beyond 13 days.
For some more on this story, the Emerging Health Threats Forum (h/t Carol@SC on the Flu Wiki) has on this study, and another on the effects of humidity on influenza viruses at:
Friday 10 September 2010
Long-lived bird flu stays on surfaces
Virus can remain infectious for up to two weeks at low temperatures
The second study:
Modeling the airborne survival of influenza virus in a residential setting: the impacts of home humidification
Theodore A Myatt , Matthew H Kaufman , Joseph G Allen , David L Macintosh , M PATRICIA Fabian and James J McDevitt
Environmental Health 2010, 9:55doi:10.1186/1476-069X-9-55
Suggests that the use of portable humidifiers might lower the survival of aerosolized influenza viruses by raising humidity indoors.
Amazingly, even in 2010, there is still much to learn about the basics of influenza viruses and how they adapt and survive in our environment.
