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West Nile Spraying Safe in Short Term: Study

California researchers found Sacramento County residents had no immediate health problems after pesticide was applied
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The UC Davis study evaluated more than 250,000 emergency-room visits to Sacramento-area hospitals during and immediately after aerial sprayings in the summer of 2005. Researchers compared patients' complaints and ZIP codes to the locations where spraying had occurred.

"Sacramento County had really good data on spraying because their planes were equipped with GPS," Geraghty said. "I could overlay on a map the spray swaths over the county ZIP codes and include the residential parcels. I could compare the parcels that were exposed to all other parcels in that ZIP code."

To make sure her comparisons were accurate, Geraghty tested them in a couple ways. For example, to make sure she wasn't overlooking any unknown diagnoses related to pesticide exposure, she compared all emergency-room diagnoses against visits for fractures and dislocations -- problems that couldn't possibly be related to spraying. "We found essentially nothing significant," she said.

She also performed a sensitivity analysis using ozone levels, to see if high ozone caused more emergency-room visits. "We could see a correlation between ozone and asthma, so I suspect if there had been a correlation with pesticides, we would have seen that as well," Geraghty said.

These findings might not apply elsewhere in the United States, where mosquito-control programs are run differently, she said.

For example, the Sacramento County program uses ultra-low-volume spraying to minimize pesticide exposure to people, with only three-quarters of an ounce or less of pyrethrin applied per acre.

"They are using the smallest effective amount of pesticide possible, about a shot glass per acre," Geraghty said. "When you think of it that way, it's a very, very small amount."

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