CDC: 7 more West Nile deaths

Death toll 71; more than 1,500 infected

Duane Allen of the East Baton Rouge Parish Mosquito and Rodent Control Department sprays for mosquitoes in a subdivision of Baker, Louisiana.

ATLANTA, Georgia (CNN) -- Seven more deaths have been linked to the West Nile virus, the Centers for Disease Control and Prevention said Tuesday.

The total number of deaths attributed to the virus this year is now 71.

The latest confirmed deaths include two in Michigan and Illinois, and single deaths in Alabama, Pennsylvania and Texas.

Illinois has the most confirmed fatalities of any state -- 18 this year. Louisiana and Michigan have 11 each.

The CDC's current nationwide fatality count does not include two deaths in Massachusetts that state health officials there reported last week. The CDC will investigate before confirming that those deaths were linked to the virus.

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The CDC on Tuesday also confirmed the first human case of the West Nile virus in Colorado this year.

More than 1,500 people have been diagnosed with the virus, federal health officials say. Thousands more have probably been infected, but most experienced only mild symptoms or none at all.

About one in 150 develops encephalitis or meningitis. Those cases generally involve people with weakened immune systems -- particularly the elderly. In those instances, the virus can prove fatal.

The West Nile virus is a mosquito-borne illness, but the CDC has determined it can be spread through organ transplants.

Health officials said they are concerned the virus also may be transmitted through blood transfusions. The CDC is investigating cases to determine whether several people nationwide were infected through transfusions.

Mosquito-control units in many states are working to clear large standing areas of water, such as swamps, where infected mosquitoes may be breeding. Officials also are encouraging people to clear small standing areas of water near their homes.

Health officials said people should wear long pants and long sleeves when outside and use bug sprays containing DEET, a chemical that may help keep mosquitoes away.