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