A sharp increase in West Nile virus infections and deaths prompted federal health officials to warn yesterday that this year's outbreak of the mosquito-borne infection will probably be much more severe than last year's.
The number of human infections more than tripled to 204 in the past week and deaths doubled to eight yesterday alone, according to the Centers for Disease Control and Prevention and state health officials. Infections have exploded in horses and mosquitoes, officials said.
"The numbers are starting to change very, very quickly," portending a much more deadly late summer and fall, said CDC Director Dr. Julie Gerberding. "We are starting the epidemic with more cases and more areas affected than last year. We could be in for a very serious affliction this summer."
Half of the deaths and more than half of the human infections have occurred in Colorado, which was largely unaffected last year, and officials expect a recurrence of the disease among states such as Ohio and Louisiana that experienced major outbreaks last year. Epidemiologists said that the outbreak is likely to reach the West Coast in full force this fall, but no cases have been reported in the region yet.
In 2002, there were a record 4,156 cases in 44 states and 284 deaths, more than in any other country. The bulk of the cases, about 65 percent, occurred in the time period corresponding to the next six weeks.
The CDC has reported 164 West Nile virus cases in 16 states. In addition, Colorado reported 39 infections yesterday and Georgia reported one case that had not yet been included in the CDC's count.
The list includes 111 cases in Colorado, 29 in Texas and 15 in Louisiana. That compares with 59 cases reported the week before, and 112 cases in four states at this point last year.
The CDC lists four deaths - two in Texas and one each in Alabama and Colorado. Colorado authorities reported three new deaths not listed by the CDC, and Georgia officials reported the first death in that state.
It is not clear why Colorado has been so strongly affected, but a wet, cool spring and a hot July have led to a sharp increase in the number of mosquitoes. Gerberding also noted that past history indicates a significant increase in cases in states during their second year of infection, as was the case in Louisiana last year. She noted that it is still too early to project how the outbreak will play out in that mountain state.
Gerberding also noted that the average age of patients has dropped, from about 55 last year to about 45 this year. That may be a statistical artifact arising from newly improved diagnostic tests, which are able to detect milder forms of the disease, she said.
Last year, about two-thirds of victims suffered from encephalitis, the more severe form of the disease that usually occurs in older people. Of the eight deaths this year, the youngest victim was 68. So far this year, only about half of the victims have had the more severe form, Gerberding said.
The increased detection of milder cases may account for part of this year's greater number of cases, she added, but not all of it.
About 80 percent of those infected develop little or no illness and never know that they are infected. A small percentage develop a severe form of encephalitis or meningitis that can be fatal, especially in the elderly.
Last year, the disease was observed in every contiguous state except Oregon, Nevada, Utah and Arizona. It is expected to strike all four of those states this year, as well as Alaska.
The rising incidence of cases makes it important for residents of the most heavily affected states, especially the elderly, to take protective steps, Gerberding said. That includes wearing long-sleeved shirts and long pants outdoors and protecting exposed areas of skin with mosquito repellents containing DEET.
People should also mosquito-proof their homes by patching or installing screens and by getting rid of objects that can hold standing water, including bird baths, tires and soda cans, she said.
The Los Angeles Times is a Tribune Publishing newspaper.