Press Releases

2003 Releases

Four in Ten Americans in High-Mosquito Areas Are Not Yet Taking Precautions Against West Nile/Mosquito Bites

For immediate release:  July 31, 2003

BOSTON, MA — A new study, conducted by the Harvard School of Public Health Project on the Public and Biological Security shortly after this year’s first human cases of West Nile virus in the U.S., finds that nearly four in ten (38%) residents of high-mosquito areas have not yet taken any precautions against mosquito bites. These findings are similar to those found at the end of last year’s outbreak of West Nile virus.

“This suggests the need for better communication by public health officials and health professionals to educate Americans on what steps they should take to protect themselves against West Nile virus,” said Robert Blendon, professor of Health Policy and Political Analysis at the Harvard School of Public Health.

The survey also shows that nearly half (48%) of people in high-mosquito areas are concerned that they or a family member may get sick from West Nile virus in the next 12 months.

These findings, based on interviews with 1,015 Americans nationwide, including 471 who said there are a lot of mosquitoes where they live, come shortly after this year’s first human case of West Nile virus in the U.S. was confirmed. So far in 2003, 44 human cases of illness from West Nile have been reported in the U.S. (as of July 30, 2003) with one confirmed death. Last year 4,156 human cases of illness from West Nile, resulting in 284 deaths, were reported nationwide. West Nile is a virus that is mainly transmitted by mosquito bites.

Precautions against Mosquito Bites

In high-mosquito areas, nearly four in ten (38%) residents report not having taken any precautions against mosquito bites since the beginning of June 2003. At the end of last year’s outbreak of the disease, a similar proportion (43%) reported not having taken any precautions. Given the number of cases of West Nile in 2002 and the fact that the disease has recurred in humans this year, this finding raises an important public health concern.

The Centers for Disease Control and Prevention (CDC) recommend using mosquito repellent containing DEET, but only 46% of Americans living in high-mosquito areas say they have used such a repellent (including the brands Off and Cutter) since the beginning of June. Three in ten (32%) have used a mosquito repellent containing citronella, and 13% report using some other kind of mosquito repellent.

Fewer than half of Americans living in high-mosquito areas report that they have taken each of four other specific recommended precautions since the beginning of June. Four in ten report having removed standing water from spare tires, gutters, bird baths, kiddie pools and other places where water collects (44%) and having avoided going outdoors at the peak mosquito hours of dawn and dusk (40%). Three in ten (30%) say they have worn long-sleeve shirts and other protective clothing outdoors. Twenty percent report having replaced or repaired window screens.

Much smaller numbers report having taken other precautions, such as using a “bug zapper” in their yard (11%) or buying mosquito netting (4%). Neither precaution has been specifically recommended by the CDC.

It cannot be determined from these results whether people are taking these precautions specifically to protect against getting the West Nile virus. In high-mosquito areas, separating general precautions against mosquitoes from those aimed at dealing with a specific mosquito-borne threat is difficult. Many people living in high-mosquito areas, in order to prevent the annoyance of mosquito bites and probably aware of other dangers such as encephalitis, would take precautions in any case. [Encephalitis is a brain inflammation that can be caused by viruses, including some carried by insects.]

Not surprisingly, far fewer residents of areas where there are not very many mosquitoes report having taken precautions against bites (32%, compared with 62% in high-mosquito areas). No more than one in five took any of the individual precautions, including using mosquito repellents that contain DEET (19%).

The complete survey can be seen here:

Charts and graphs can be seen here:

Tables can be seen here:

(For information about preventive measures, go to the CDC website,

The survey was supported by a grant from the Centers for Disease Control and Prevention to the Harvard Center for Public Health Preparedness.

This study was designed and analyzed by researchers at the Harvard School of Public Health. The project director is Robert J. Blendon of the Harvard School of Public Health. The research team also includes John M. Benson, Catherine M. DesRoches, Elizabeth Raleigh, and Kathleen Weldon of the Harvard School of Public Health and Melissa J. Herrmann of ICR/International Communications Research. Fieldwork was conducted via telephone for the Project by ICR/International Communications Research of Media (PA) between July 18 and July 22, 2003. The survey was conducted with a nationally representative sample of 1,015 adults age 18 and over, including 471 who said they lived in areas where there are a lot of mosquitoes. The margin of error for the total sample is plus or minus 3 percentage points; for residents of high-mosquito areas, plus or minus 4.5 percentage points.
Possible sources of nonsampling error include nonresponse bias, as well as question wording and ordering effects. Nonresponse in telephone surveys produces some known biases in survey-derived estimates because participation tends to vary for different subgroups of the population. To compensate for these known biases, sample data are weighted to the most recent Census data available from the Current Population Survey for gender, age, race, education, as well as number of adults and number of telephone lines in the household. Other techniques, including random-digit dialing, replicate subsamples, callbacks staggered over times of day and days of the week, and systematic respondent selection within households, are used to ensure that the sample is representative.


For further information, please contact:

Robin Herman
Office of Communications
Harvard School of Public Health
677 Huntington Avenue
Boston, MA 02115
Phone: 617-432-4752