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Number of West Nile Virus Cases Higher in U.S. in 2005

CDC recommends ongoing surveillance and prevention strategies

TUESDAY, Dec. 20 (HealthDay News) -- There were 2,744 cases of West Nile virus (WNV) reported in the United States in 2005, an increase from 2,359 cases in 2004, according to a report in the Dec. 16 issue of the Morbidity and Mortality Weekly Report. Overall, 42 states reported human cases of WNV, with California representing about a third of these.

The U.S. Centers for Disease Control and Prevention says that ongoing surveillance and prevention of the mosquito-borne infection is essential.

Of the 2005 cases, 42.5% were neuroinvasive disease such as meningitis, encephalitis, or acute flaccid paralysis and 52.2% were WNV fever, with most cases occurring in the elderly. However, the CDC notes that 80% of infections are asymptomatic, with about 20% leading to WNV fever and less than 1% leading to neuroinvasive disease. The majority of cases of neuroinvasive disease required hospitalization, with 7.3% deaths, while only 22% of WNV fever cases required hospitalization and resulted in 0.3% deaths. The data were collected using ArboNET, an Internet-based surveillance system operated by CDC and state health departments.

Twenty-one counties that had not previously reported WNV had cases of disease in animals or humans. "The increase in reported cases of WNV disease in 2005 compared with 2004 suggests that endemic transmission of WNV in the United States will continue for the foreseeable future," the CDC notes. "In the absence of an effective vaccine, prevention of WNV disease depends on community-level mosquito control and promotion of personal protection against mosquito bites, such as use of repellents, and avoiding outdoor exposure when mosquitoes are active."

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