West Nile Virus, transmitted by mosquito bites, has emerged as a major health concern, punctuated by its spread across the continental United States. Last year, the Centers for Disease Control and Prevention reported 264 deaths and 9,862 people who became sick from the virus. That has led many communities to spray for mosquitoes. From July to September 2000, the New York City Department of Health and Mental Hygiene sprayed sumithrin, a pyrethroid-based pesticide. Pyrethroid pesticides have been reported to aggravate the symptoms of asthma; death has resulted from exposure in some cases, so a group of researchers looked at its effects on New Yorkers' health.

What the researchers wanted to know: Does spraying with sumithrin increase the number of asthma-related emergency room visits?

What they did: The researchers counted up asthma-related emergency room visits to public hospitals from October 1999 to November 2000 and correlated them by ZIP code. All boroughs, except Staten Island, which does not have a public hospital, were analyzed. (The numbers were controlled for environmental variables, including ozone, temperature, and precipitation.)

What they found: Emergency room visits for asthma to public hospitals did not significantly increase after spraying of sumithrin.

What this study means to you: Spraying sumithrin in these amounts may not be a problem for asthmatics. More communities could consider putting sumithrin in their arsenals against mosquitoes.

Caveats: If they knew the spray was coming, asthmatics may have avoided their neighborhoods, stayed indoors, or taken asthma medicine prophylactically to ward off ill-effects of the spraying. . Less severe reactions may have occurred, which were not observed in hospitals.

Find out more: The CDC has a website that tracks the spread of West Nile Virus: www.cdc.gov/ncidod/dvbid/westnile

Read the article: Kaparti, A.M., et al. Pesticide Spraying for West Nile Virus Control and Emergency Department Asthma Visits in New York City, 2000. Environmental Health Perspectives. August 2004, Vol. 112, No. 11.

The article is available free online: http://ehp.niehs.nih.gov