Avian-flu virus unlikely to spread through wastewater and drinking-water treatment systems.

Researchers have found that commonly used wastewater and drinking-water treatments, including chlorination, ultraviolet (UV) radiation, and bacterial digesters, can eliminate H5N2, a close relative of the highly pathogenic avian-influenza virus H5N1. H5N2 is harmless to humans but provides a study case of the pathways by which the influenza could spread to human populations.

Cornell researchers studied H5N2, a low-pathogenic avian-influenza virus that is not contagious for humans, to see whether a hypothetical mutated form of H5N1 could infect people through drinking-water and wastewater systems. The U.S. Military Academy at West Point collaborated on the study, and the results were published under the title "Inactivation of the Avian Influenza Virus (H5N2) in Typical Domestic Wastewater and Drinking Water Treatment Systems" in the November 2006 issue of Environmental Engineering Science.

H5N2 is physically similar to H5N1, which has been lethal to millions of birds globally and more than half of the almost 200 people who have been infected, mostly through handling of infected birds, since 2003. Researchers and officials are concerned that if H5N1 mutates to a form that can be transmitted easily between people, a deadly global pandemic could occur.

"It is unknown if H5N1 is more resistant than H5N2 to procedures used by the water management industry," said Araceli Lucio-Forster, Ph.D., the lead author of the study and a teaching support specialist in Cornell's Department of Microbiology and Immunology.

Because experiments with H5N1 require high-level biosafety facilities, Lucio-Forster and colleagues used H5N2 as a surrogate. Given the similarities between the two viruses, she thinks that if H5N1 entered the water treatment system, the virus would be inactivated--"which means treated water may not be a likely source of transmission," she said.

Overall, avian flu viruses do not survive well outside of a host. Still, the researchers tried to address concerns in the wastewater-treatment industry that if a human outbreak occurred, contaminated feces passing through the plant could infect plant workers and spread elsewhere through drinking water.

"You have some 50,000 treatment plants in the United States, and all these operators who run the plants were concerned that if there were an influenza outbreak and everyone were sick, it might come into the plant and infect them and others," said co-author Dwight Bowman, a professor of parasitology at Cornell.

To test the effectiveness of UV radiation for killing the H5N2 virus, the researchers exposed the virus in drinking water, as well as in wastewater effluents, to UV light at varying levels. The treatment was very effective in killing H5N2 at UV levels well within industry standards (and at lower levels than are used for killing Cryptosporidium and Giardia in water).

With chlorine, which is almost ubiquitous in U.S. drinking water, the results were less definitive. Inactivation of H5N2 depends both on chlorine concentration and on time of exposure. On average, U.S. treatment plants treat drinking water with chlorine concentrations of 1 milligram per liter for 237 minutes. Under these conditions, the researchers found that H5N2 (and probably H5N1) would be mostly inactivated, but further studies are needed to see if the viruses stay active when they come out of feces or when pH and salinity levels are different.

The small laboratory-scale study found that bacterial digesters reduced H5N2 to undetectable levels after 72 hours, which is consistent with industry standards. The researchers also found that higher digester temperatures inactivated the virus more quickly.

The UV and chlorine tests were conducted at the U.S. Military Academy.

Adapted, with permission, from the Cornell Chronicle (January 2, 2007), a publication of Cornell University.