West Nile rapidly invading the US

Aug 12, 2003 (CIDRAP News) – Officials from the Centers for Disease Control and Prevention (CDC) warned on Aug 7 that the number of West Nile cases (153) had tripled during the first week of August and that the disease appeared to be spreading rapidly across the United States. Just since that time, the number of cases has more than doubled again. In the Aug 7 telebriefing, Dr. Julie Gerberding, director of the CDC, said, "There are more cases already this year with human disease compared to the same time last year. And I think this is one picture of the situation that we are very concerned about, and it tells us that we need to really step up the effort to control mosquitoes and to prevent mosquito bites."

Nationwide there have been 367 cases of West Nile and nine deaths, Dr. Susan Montgomery, epidemic intelligence officer in CDC's Division of Vector-Borne Infectious Diseases, told CIDRAP News this afternoon. The median age for those who have died is 82 years, with a range of 67 to 85.

Colorado is reporting the highest number of cases in the nation, with 195 as of today. Five deaths have occurred there, all of them in women between the ages of 67 and 84, according to Lori Maldonado, a spokesperson for the Colorado Department of Public Health and Environment (CDPHE). Last year at this time, Colorado did not have any human cases of illness or death associated with the virus.

The West Nile virus is in the Flaviviridae family. It is carried by mosquitoes, and birds serve as a reservoir host. Humans and other mammals do not transmit the virus.

Anyone can contract West Nile, but people over age 50 are more susceptible, according to the CDC. The vast majority of people who are infected with the virus show no symptoms. Approximately 20% will have mild symptoms including fever, headache, nausea, and sometimes swollen lymph glands and a rash on the chest, stomach, and back. Serious illness develops in only about 1% of those infected; symptoms include high fever, stupor, coma, tremors, muscle weakness, and paralysis. These symptoms may last for weeks and neurologic effects can be permanent.

Comparing the impact of the virus state-by-state can be difficult because the CDC does not have a mandatory case definition for reporting West Nile. Consequently, some states report only serious cases such as encephalitis, meningitis, or death. Others report milder cases as well. According to Montgomery, most states report both mild and severe cases, and the CDC is interested in all West Nile data the states are willing to report.

Dr. Ken Gershman, chief of Colorado's communicable disease program, told CIDRAP News that Colorado has "a very complete surveillance system, and we include West Nile fever cases as well as the more serious cases. Other states may choose not to include the less serious cases, but we do." He added that of the 195 West Nile cases in his state, about 40 are meningitis or encephalitis.

Nationwide, there are some notable differences in the West Nile cases this year compared with last, Gerberding said at the Aug 7 press conference. The median age of those people diagnosed with West Nile had dropped to 45 by that date, down from 55 in 2002. In addition, more states are reporting human activity this year. In 2002, only four states had reported human cases, so far this year there are 20.

Public health officials at the state and federal levels advise that the best protection from West Nile is to avoid being bit. "We are advising Colorado residents to use insect repellant with DEET, avoid being outside at dusk and dawn when mosquitoes are actively feeding, wear long-sleeved shirts and pants, and remove standing water where mosquitoes breed," said Maldonado.

The CDC recommends that people choose insect repellant with a DEET concentration appropriate for the amount of time they expect to be outside. A higher concentration of DEET provides longer protection, not better protection: DEET with a 6.65% concentration is effective for about 2 hours and a 24% solution is effective for about 5 hours, according to the CDC. DEET with a concentration up to 30% can be used on children over 2 months of age, according to the American Academy of Pediatrics.

See also:

CDC case count (numbers had not been updated to match those above at time of publication)

Colorado reported cases

CDC West Nile Home Page

Transcript of Aug 7 CDC telebriefing

Information on DEET

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