ATLANTA (AP) – The number of West Nile virus cases has tripled to at least 164 since last week and will likely break last year’s record, a top federal health official said Thursday in the latest warning about the rapid advance of the mosquito-borne disease.

“The numbers are starting to change very, very quickly,” said Dr. Julie Gerberding, head of the Centers for Disease Control and Prevention. “That is very concerning.”

State health officials report seven people – all of them elderly – have died from the virus. Four of the deaths were reported in Colorado, the hardest-hit state.

Health officials had expected the disease to spread this year to all corners of the country, invading Western states previously unscathed. But they appeared somewhat surprised at its speed.

“It indicates we are starting the epidemic with more cases than last year,” Gerberding said. She warned of “a great number of infected people.”

Nationwide, the CDC said at least 164 people in 16 states are infected, compared with 59 a week ago. The latest figures do not include new cases reported by Colorado health officials, which the CDC had not verified.

Last year’s numbers

Last year, 4,156 people caught the virus, and 284 died. There were 112 cases in four states at this point in 2002, when the United States suffered the biggest reported outbreak of West Nile encephalitis in the world.

West Nile virus rarely kills, but about 1 in 150 people who get it will develop its potentially deadly encephalitis or meningitis. Most often, it affects the elderly. Of its seven victims this year, the youngest was 68.

Why four of those occurred in Colorado, which reported 154 cases Thursday, is somewhat a mystery. Some experts blame the outbreak on a wet June and very hot July, which they say provided the perfect summer for mosquitoes.

“I can’t predict what will happen in Colorado, nor can I completely explain why it is happening,” Gerberding said.

Colorado different

Colorado differs from others because it reports all confirmed cases, including mild cases that some states do not report, said state epidemiologist John Pape. The CDC has only confirmed 72 Colorado cases.

Last year, that state had about a dozen cases. Four states – Arizona, Utah, Nevada and Oregon – had no signs of the disease in man or animal.

“If it can increase that dramatically in Colorado, it has the potential to do so in Arizona,” said Craig Levy of the Arizona Department of Health Services. “That certainly makes us very nervous.”

Until Colorado’s first death a week ago, the virus had never killed anyone west of the Great Plains states.

The CDC is urging people in the 16 states where the virus has appeared to use mosquito repellent, cover arms and legs with clothing and avoid early morning and evening hours when mosquitoes are most active.

Those states are Alabama, Colorado, Florida, Iowa, Kansas, Kentucky, Louisiana, Minnesota, Mississippi, Nebraska, New Mexico, North Dakota, Ohio, South Carolina, South Dakota and Texas.

Since West Nile first entered this country through New York in 1999, health officials have tried everything – mosquito spraying and other control efforts, prevention messages and disease detection systems.

But there’s no way to prevent the virus from spreading and there’s no way to predict which areas it will strike hardest, said Dr. Sue Montgomery of the Centers for Disease Control and Prevention.

Last year, Louisiana had more than 300 cases and 25 deaths from the virus. They did “everything … according to the book and we had a large epidemic,” recalls Dr. Raoult Ratard, state epidemiologist for the Louisiana Department of Health and Hospitals.

“It’s like a viral hurricane.”

Most people who are infected with the virus won’t get sick. The CDC says about a fifth of those will develop a fever, headache, body aches and sometimes a rash and swollen lymph glands.

Symptoms for West Nile encephalitis or meningitis include headache, high fever, neck stiffness, disorientation and sometimes paralysis.

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On the Net:

CDC info: http://www.cdc.gov

AP-ES-08-07-03 1921EDT