How Common Was West Nile Virus in St. Louis? Researchers Look for the Answer

ST. LOUIS -- Saint Louis University researchers and other public health officials have begun a new study to gain a clearer picture of how many people in St. Louis were infected with the West Nile virus during the past two mosquito seasons.

By taking blood samples from approximately 1,000 people living in the St. Louis metropolitan area for evidence of past infection, researchers hope to estimate how many people were infected with West Nile virus (WNV) during 2002 and 2003. This will be achieved by looking for WNV antibodies in the blood samples and using those results to estimate the WNV infection rate for the region.

Researchers also hope to determine how effective are various surveillance methods in predicting areas that may be at higher risk for WNV infection; and show what specific factors, such as mosquito-avoidance behaviors, are associated with infection risk.

Recruitment began this week, and the study must be concluded in early summer, before the height of the new mosquito breeding season.

"We plan to enroll approximately 1,000 people," said Dr. Brooke Shadel, an assistant professor of public health at Saint Louis University School of Public Health and the study's lead investigator. "Participants will be asked to answer a few survey questions and provide a single tube of blood. We are hopeful that people will be interested in participating if we come to their door. They will be able to find out if they have been previously infected with WNV and will be able to contribute to advancing our knowledge about how to respond to this disease at a community level."

The teams will take blood samples from people living in areas that appear to be at lower risk for WNV, and compare these samples to samples from people in higher-risk areas.

The study includes randomly selected households in communities that have experienced a large number of dead birds or WNV-infected mosquitoes, and households in areas where there were few dead birds or infected mosquitoes. Study teams, consisting of an interviewer and a trained phlebotomist, visit these randomly selected homes and ask if one person in the household will agree to provide survey information and donate one tube (about two teaspoons) of blood for the study.

After the blood draw, participants are asked a few survey questions, which is standard in studies like this one. The survey gathers basic demographic information, but also includes an assessment of possible routes of exposure to mosquito-borne illness, possible risk factors for WNV-related illness, and questions that help rule out infections that would have occurred outside the St. Louis metro region.

"We have been assuming that the majority of human infections are occurring where there has been a lot of bird and mosquito activity, but this hasn't been proven," Shadel said. "That's where this study comes in. The results of this study will help us to confirm if these surveillance methods are truly early markers that can predict where human infections will occur sort of like a canary in a coal mine. If these methods are early markers, resources for prevention could be more effectively focused in those higher risk areas."

The blood samples will only be tested for infections transmitted by mosquitoes, including WNV. Information gathered during the survey and all blood test results will be kept confidential and used only for the study. No identifying information will be shared outside of the study and results detailed in the final study report will be in aggregate form and not show any identifiers.

Funded by a grant from the Centers for Disease Control and Prevention (CDC), the study is being coordinated among members of Missouri's West Nile Virus Working Group. The Missouri Department of Health and Senior Services (DHSS), Saint Louis University School of Public Health (SLUSPH), St. Louis City Health Department, and St. Louis County Department of Health are conducting the study.

Source: Saint Louis University Health Sciences Center

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