Missouri Department of Health & Senior Services
April 29, 2004

Office of the Director
912 Wildwood
P.O. Box 570
Jefferson City , MO 65102

Telephone: (800) 392-0272
Fax: (573) 751-6041
Web site: www.dhss.state.mo.us

West Nile Virus Infection to be Studied

Public health officials are conducting a new research study this spring to gain a clearer picture of how much West Nile virus infection actually has occurred in the city of St. Louis and Saint Louis County the past two mosquito seasons. 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), St. Louis University School of Public Health (SLUSPH), St. Louis City Health Department, and St. Louis County Department of Health are conducting the study.

The West Nile virus (WNV) study involves testing blood samples from about 1,000 persons living in the St. Louis metropolitan area for evidence of past WNV infection. Study teams 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. Recruitment began this week, and the study must be concluded in early summer, before the height of the new mosquito-breeding season.

Study leaders hope to meet a number of objectives, including:

• Estimate how many people were infected with WNV in the St. Louis metro area during the 2002 and 2003 combined transmission seasons. 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.

• Determine how effective various surveillance methods are in predicting areas that may be at higher risk for WNV infection.

• Seek to show what specific factors, such as mosquito-avoidance behaviors, are associated with infection risk.

It is estimated that more than 80 percent of all WNV infections go unnoticed. One in five infected people will have a mild flu-like illness, and only about one out of 150 infections results in illness requiring hospitalization. However, risk of severe illness from WNV infection is higher in the elderly and people with compromised immune systems.

"There is so much we don't know about WNV and we really hope this study will give us an advantage in fighting a disease that promises to be around for a long time to come," said Dr. Howard Pue, state public health veterinarian and DHSS study coordinator. "Because there is no vaccine or direct treatment for WNV, our best weapon against it is prevention. We hope this study will tell us more about what factors create higher infection risk and what methods are most effective for predicting high-risk areas and populations. With that information we can then create more effective prevention strategies against WNV."

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. Participants must be at least five years old and be able to provide either written informed consent or have an adult guardian who can provide consent and answer the survey questions. The only persons who are excluded from the study are those who have not lived at their current address since June 2002, and those who have known bleeding disorders, since blood samples will be taken from an arm vein. Participants are given free WNV educational material that outlines strategies that may help reduce their risk of future infection. Then, later in the study, they will be able to learn the results of their blood test.

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.

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.

"We have assembled an exceptional group of interviewers and phlebotomists and are excited about kicking off this study," said Dr. Brooke Shadel, St. Louis University School of Public Health and the study's lead investigator. "The idea for the study came from many discussions with the West NileVirus Working Group over the past two years. Throughout the season, the working group met regularly to share information and develop a response plan to this public health threat. As part of the response, several surveillance methods were implemented to measure levels of WNV activity, including tracking dead bird reports, trapping mosquitoes to look for the virus and evaluating the reported human cases."

"We have assumed 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. 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," said Shadel.

Shadel added, "We plan to enroll about 1,000 people. 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." Shadel said study teams will work only during daylight hours and will complete their work each day by 8 p.m. to limit disrupting households in the evening and for the teams' own safety. The teams will wear official identification and will clearly identify themselves when making a house call. The St. Louis City Police Department and the police departments of The municipalities in St. Louis County will also be notified of the study and the teams' work throughout the city and county.

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