With 14 confirmed deaths from West Nile virus and about 324 human cases in 16 states, federal public health officials Friday said they expect the outbreak to peak by mid-September.
The virus continues to spread with new cases reported Thursday in horses in Montana and New Mexico.
Illinois reported 16 positive laboratory tests for the mosquito-borne illness, bringing to 42 the number of human cases in that state, including two deaths. The second death was a 67-year-old suburban Chicago woman who died Aug. 18, said Dr. John Lumpkin, state public health director.
Texas has 28 confirmed cases and one death, Louisiana 171 cases with eight deaths, Mississippi 64 cases and three deaths, and Kentucky one fatal case reported earlier this week.
Ohio had four confirmed cases and 9 probable victims, eight cases involving people under 50. Health officials in Kansas City reported Kansas' first suspected human case, a 24-year-old woman.
Indiana reported three more probable cases of the West Nile virus Friday. The state already had one confirmed case and three probables being tested.
The average age of a West Nile victim was 53, about 10 years younger than in previous outbreaks. The first West Nile outbreak in the United States occurred in 1999 and killed seven people in the New York City area.
The Centers for Disease Control and Prevention said the virus had killed more than 3,400 birds in 38 states and infected 255 horses in 19 states. Montana reported its first equine case of the virus. Two horses were infected in New Mexico. Like yellow fever and related viruses, biting mosquitoes spread West Nile from infected birds and animals to people.
"Once you get infected with those viruses you have immunity for life, so we might expect the same thing to occur with West Nile virus," Lyle Petersen, a medical epidemiologist with the CDC told Friday's Milwaukee Journal-Sentinel.
Petersen said with cooler fall weather approaching that the West Nile outbreak may peak in the next couple of weeks, but re-appear next summer. He said the outbreak likely would reach California.
Louisiana health officials reported 24 new cases Friday but no new deaths, bringing the confirmed total to 171 human cases and eight deaths.
Over the past three weeks the number of victims with severe cases of the virus in Louisiana have declined, officials said, but they were not prepared yet to say that the disease has peaked in the state.
"There is a greater demand to have anyone with even minor symptoms tested for WNV," said Dr. Raoult Ratard, state epidemiologist. "So possibly, this could be contributing to the fact that we're seeing a greater number of less severe cases. Or, it could be evidence that the outbreak is subsiding. Today, I am encouraged, but we will watch the trends for several more weeks before making a definitive prediction as to the direction the outbreak is headed."