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Number of West Nile cases in Travis County decreasing

Wednesday, September 19, 2012 by Josh Rosenblatt

After three deaths and dozens of reported cases, it looks like Travis County’s long summer of West Nile Virus may be winding down.

The number of reported cases of the mosquito-borne virus in the county has dropped considerably since peaking almost exactly one month ago, according to the Austin/Travis County Health and Human Services Department.

“We’re hoping we’re on the downward slide of this particular outbreak,” the department’s chief epidemiologist, Janet Pachette, told Austin City Council’s Health and Human Services Committee on Tuesday.

As of Tuesday, the HHS department had investigated 90 cases of West Nile in the county. That’s about 4 per 100,000 citizens. Which is high but considerably lower than the 12 per 100,000 seen in Dallas (where authorities opted for aerial pesticide spraying) and the 60 per 100,000 seen in some parts of West Texas. Fifty of those 90 patients in Travis County were diagnosed with West Nile Fever, the other 40 with the far more dangerous West Nile Neuroinvasive Disease. Fortunately, about 80 percent of those affected with the virus are asymptomatic.

Three West Nile-related deaths have been reported this year in Travis County.

Human data indicates a downward trend in the number of confirmed cases since Aug. 25, down to about five during the first week in September, while surveillance done by the department’s chief sanitarian, David Lopez, and his staff indicates a downward trend in positive mosquito pools around the county.

Back in mid-July, health officials were finding about 20 positives pools a week. Between Sept. 10 and 14, only two such pools were reported by HHSD staff.

All told, Travis County has seen 113 pools testing positive for West Nile Virus this summer, the highest number the county has seen since such surveillance began in 2003.

Considering this year’s high numbers, the length of Austin summers and positive pool detection started nearly a month earlier than normal, committee members understandably had concerns that the HHSD’s trend lines might not hold up.

Council Member Chris Riley, for one, asked whether department optimism that the recent “cold snap” might further diminish the number of virus-positive mosquitoes might be offset by the corresponding uptick in rain.

“It’s encouraging to think we’re passed the worst of the summer and we’re seeing the lines go down,” Riley said. “I’m curious as to whether the wet weather also has an impact, whether we might see spikes after rains. Would you expect that might lead us to any reversal in the trend, or is it more temperature-related than precipitation-related?”

Pichette responded that though the precipitation could potentially lead to an increase in the mosquito population, she believes that “lower temperatures will definitely diminish some of the mosquitoes.”

Both Riley and committee Chair Mike Martinez wondered about the possibility and the potential dangers of aerial spraying, a course health officials rejected in August. Martinez, in particular, wanted to know who would make such a decision, and under what authority, should the downward trend unexpectedly shift upward. Knowing the answer to those questions, he said, could help allay citizens’ fears, both about the virus and about the perceived problems associated with aerial spraying.

“Is this a collective decision or an individual decision?” Martinez asked. “How does Council retain that authority? I don’t mean to be an alarmist but these are the concerns that I think the public would want to understand.”

According to HHSD Director Carlos Rivera, the decision ultimately lies with the HHSD health authority, Dr. Philip Huang. “According to our policy and state statutes, it’s a health authority decision,” Rivera told the committee. “But it’s something Dr. Huang would do in consultation with our leadership … and with the state Health Department.”

Huang appeared confident that the time to consider spraying has passed.

“We do think we’re on the downward side of this, but we are continuing to monitor (it),” Huang said. “But we don’t think aerial spraying will be necessary.”

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