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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THURSDAY, July 11 (HealthDay News) -- California residents apparently suffered no immediate ill health effects from aerial pesticide spraying intended to prevent the spread of West Nile virus in Sacramento County in 2005, a new study shows.

Researchers found no increase in emergency-room visits for ailments linked to aerial spraying, including respiratory, gastrointestinal, skin, eye or neurological conditions, said study author Dr. Estella Geraghty, an associate professor of clinical internal medicine at the University of California, Davis.

"The good news is that the aerial application of pyrethrin does not appear to increase emergency-room visits for any kind of complaint," Geraghty said.

Geraghty added that this was the first attempt to study the public health implications of aerial spraying to control mosquito populations. The findings were published recently in the journal Public Health Reports.

Mosquitoes carry and transmit West Nile virus, which causes fever and sickness in about 20 percent of people infected. In rare cases, it can lead to potentially fatal neurologic illnesses like encephalitis or meningitis.

California first began aerial spraying for mosquitoes following a West Nile outbreak in the summer of 2005, a program that generated some controversy. The pesticide they used, pyrethrin, is also used to treat head lice in children and to prevent flea and tick infestation in pets, according to the study authors.

"I think people feel this lack of control when pesticides are being sprayed from the air," Geraghty said. "They don't feel they can avoid it, like they can when someone is spraying pesticide from a truck or tractor."

Geraghty cautioned that her study did not consider the long-term effects of pesticide exposure. "This doesn't mean that chronic injury from pesticides is not possible," she said. "It's also possible that people felt ill but didn't go to the ER, or went to their private provider."

That's an important caveat for Mike Somers, California state director of the environmental group Pesticide Watch.

"In the positive, it's always great to see studies that are looking at the health effects of pesticide use," Somers said. "But it's not just the short-term effects of pesticides we are worried about. A lot of the time we don't know what the long-term effects are. We also don't have a very good idea of what the composite picture is -- multiple exposures to different pesticides."

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."

More information

For more information on West Nile virus, visit the U.S. Centers for Disease Control and Prevention.

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