Demographics of West Nile virus victims studied

Tuesday, November 19, 2002

JEFFERSON CITY, Mo. -- With the coming of cold weather, the mosquitoes are gone and the analysis is wrapping up on this year's outbreak of the West Nile virus.

This much is known, according to state health department statistics:

- Across Missouri, 169 people were confirmed through state or private health labs to have come down with the mosquito-borne virus.

- The average West Nile virus victim was 53 years old, most likely from the St. Louis area and slightly more likely to be a man than a woman.

- Most of the cases were contracted in August, which happened to be the wettest month of the summer.

So what does that mean?

"A lot of that is still under investigation," Dr. Howard Pue, chief of the health department's communicable disease section, said Monday.

There are several curious aspects to the West Nile virus demographics.

For example, it has usually been suggested that older people are more susceptible to the disease's serious symptoms, such as brain swelling that can lead to death.

In years past, the average age nationally of West Nile virus victims was around 68, Pue said. This year's average age of 53 in Missouri is an indication not only that people of all ages are being affected, but that doctors are starting to detect more routine cases in younger people and send blood samples in for laboratory testing, Pue said.

Nearly all people afflicted with West Nile virus reported a fever. Most also had a headache, fatigue, poor appetite, muscle weakness and nausea, according to health department figures for 133 completed case studies. Other case studies are ongoing.

Most interesting to health department epidemiologist Fazle Khan is the fact that 70 percent of the 169 confirmed cases occurred in St. Louis city and county, which comprise slightly less than one-quarter of the state's population.

"It baffles me and baffles everybody here," said Khan, adding that the state was studying the potential reasons for the disparity.

Although not scientifically certified, Pue offered a couple of possible explanations. West Nile virus was first reported in Missouri last fall in the St. Louis area, meaning the disease already had a foothold there for this summer.

Also, Pue said, St. Louis has a natural mosquito breading ground in some of the marshy areas created by the Mississippi and Missouri rivers. Mosquitoes also may have found water puddles in old cans, tires or other objects in the vacant lots of St. Louis, he said.

Pue said the state also was studying whether St. Louis has a greater population of the mosquito species that are most likely to transmit the virus.

According to the health department figures, 54 percent of West Nile virus cases statewide occurred in men, who according to the 2000 census are a slight minority compared to women.

Khan said one explanation for the difference is that men -- by virtue of their work or recreation -- spend more time outdoors than women.

As for the late summer outbreak of the virus, Pue said that is consistent with previous national findings.

Pue said the demographic data on West Nile victims can help the state develop strategies to fight the disease, which most likely will be back next summer.

"We have to know who is being affected, who is being affected the most severely, where these people live, how they are being exposed, what the risk factors are," Pue said. "We need to combine this type of surveillance data with prevention and control activities."

A look at the human West Nile virus cases reported this year in the nation and in Missouri.

MISSOURI CASES

St. Louis County, 61

St. Louis city, 56

St. Charles County, 7

Kansas City, 5

Cole County, 4

Jefferson County, 3

Callaway County, 2

Cass County, 2

Crawford County, 2

Independence city, 2

Laclede County, 2

Miller County, 2

St. Francois County, 2

Bollinger County, 1

Boone County, 1

Cape Girardeau County, 1

Dunklin County, 1

Franklin County, 1

Jackson County, 1

Lafayette County, 1

Mississippi County, 1

Monroe County, 1

Morgan County, 1

New Madrid County, 1

Newton County, 1

Nodaway County, 1

Pettis County, 1

Platte County, 1

Pulaski County, 1

Saline County, 1

Scott County, 1

Washington County, 1

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