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Sacramento County may have seen the worst of West Nile virus for 2005.
State and local health officials said Tuesday the peak transmission period has passed for this season, a year in which Sacramento County's high caseload led the state.
OAS_AD('Button20'); While cases will continue to be logged well into October, the numbers of new cases reported each week to the state has begun to wane, and with it, a controversial episode in local public health policy.
Sacramento County's epidemic dominated public health concerns this summer, igniting an outcry among people opposed to aggressive mosquito control tactics that included unprecedented aerial pesticide spraying.
The high infection rate was predicted for Northern and Central California as early as last year, after Southern California bore the brunt of the virus in 2004. The virus hit this region last year, its presence signaled by dead birds in the hundreds.
But this year, West Nile made the jump to the human population because of a surge in the number of mosquitoes, which spread the disease, feeding on dead birds, then biting humans. Mosquito breeding was aided by a heavy spring rainfall and snowmelt combined with hot temperatures in July.
"We are now past the peak transmission period," said Dr. Vicki Kramer, chief of the vector-borne disease section of the state Department of Health Services. "However, the public needs to keep in mind, based on our experience last year and on those of other areas, that people can get infected in September and October."
Statewide, the total of human cases Tuesday reached 618 for 2005, an increase of 19 percent from 521 a week ago.
Sacramento County reported Tuesday a total of 135 cases, up 19 since last Tuesday, a 16 percent increase. That differs dramatically from the weekly jumps in August, when case totals bounced by 20 to 50 percent. "This is a cautious comment,"
said county health officer Dr. Glennah Trochet, "but it looks like we have had fewer (recently) than we have had in the past. But one point in time doesn't make a trend."
While it appears the number of new cases statewide is dropping, Kramer also cautioned that until the first hard, cold rain, it's still West Nile season.
Data collected so far can be misleading because it can be a month or more before a case shows up on the record books, she said. The incubation period for West Nile virus is about five to 14 days.
A person can get bitten, not get sick for a week and not seek medical attention until symptoms worsen.
Last year, the peak period of transmission occurred in the first two weeks of August, Kramer said. She suspects this year's peak occurred in the latter two weeks of August, the delay due to a spate of cooler weather, which slowed virus transmission.
Symptoms of West Nile virus may include fever, headache, body aches and rash - some of which can be debilitating and last up to several weeks. But only 20 percent of those infected will ever experience symptoms.
The more serious infections, which can affect the central nervous system and result in meningitis, encephalitis and a polio-like syndrome, affect only 1 in 150 people infected. Symptoms of the more serious infections may include a stiff neck, slight or partial paralysis, altered mental status and coma.
Trochet and Kramer credited mosquito control efforts for what appears to be a relatively mild West Nile virus season compared to other states during the height of their infections.
Kramer cites Colorado, a far less populous state, where nearly 3,000 people became infected in 2003, leading to 63 deaths. In California, nine people have died from West Nile virus this year, including one Sacramento County man. The most recent death, that of an unidentified elderly woman in Kings County, occurred last week.
"The important point here is that without the intensive mosquito control in California, I am quite certain we would be seeing more illness and death associated with West Nile virus," Kramer said.
The sudden spike in Sacramento County cases thrust the Sacramento-Yolo Mosquito and Vector Control District to center stage. Unprepared for public scrutiny, the district nevertheless stuck by its spraying strategy.
The district's aggressive approach - which in Sacramento County included unprecedented aerial spraying of pesticides in urban areas - generated protests and criticism.
Protesters questioned the potential effects of the poison on children, pets, cars and other items exposed to the outdoors. And they grew increasingly frustrated as planned spraying was thwarted night after night by high winds.
The complaints led to an agreement among mosquito and vector control officials to better inform residents of mosquito control efforts on the ground and in the air.
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