West Nile Virus Activity --- United States, August 8--14, 2002, and Mississippi, July 1--August 14, 2002

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET and by states and other jurisdictions as of August 14, 2002.

United States

During the reporting period of August 8--14, a total of 44 laboratory-positive human cases of WNV-associated illness were reported from Mississippi (n=20), Louisiana (n=14), Alabama (n=three), Texas (n=two), Florida (n=one), Illinois (n=one), Indiana (n=one), Massachusetts (n=one), and the District of Columbia (n=one). During the same period, WNV infections were reported in 382 dead crows, 310 other dead birds, 52 horses, and 362 mosquito pools.

During 2002, a total of 156 human cases with laboratory evidence of recent WNV infection have been reported from Louisiana (n=85), Mississippi (n=48), Texas (n=14), Alabama (n=three), Illinois (n=two), Florida (n=one), Indiana (n=one), Massachusetts (n=one), and District of Columbia (n=one). Nine deaths have been reported from Louisiana (n=seven) and Mississippi (n=two). Among the 154 patients with available data, the median age was 54 years (range: 3--94 years), and the dates of illness onset ranged from June 10 to August 13.

In addition, 1,458 dead crows and 1,137 other dead birds with WNV infection were reported from 37 states, New York City, and the District of Columbia (Figure 1); 139 WNV infections in horses have been reported from 15 states (Alabama, Florida, Georgia, Illinois, Kansas, Kentucky, Louisiana, Minnesota, Mississippi, Nebraska, North Dakota, Ohio, South Dakota, Tennessee, and Texas). During 2002, WNV seroconversions have been reported in 62 sentinel chicken flocks from Florida, Nebraska, and Pennsylvania; 787 WNV-positive mosquito pools have been reported from 13 states (Alabama, Georgia, Illinois, Indiana, Massachusetts, Mississippi, Nebraska, New Jersey, Ohio, Pennsylvania, South Dakota, Texas, and Virginia), New York City, and the District of Columbia.

Mississippi

During July 1--August 14, the Mississippi State Department of Health (MSDH) identified 48 human cases with laboratory evidence of WNV infection (Figure 2). Using the surveillance case definition, 31 cases were laboratory confirmed and 17 were probable. Of the two reported deaths, one was attributed to WNV infection; the second is under investigation.

The 48 patients had a median age of 55 years (range: 3--89 years); 58% were male. Initial clinical data indicate that 46 (96%) of the patients had WNV-associated meningoencephalitits. The two remaining cases are under evaluation.

Of Mississippi's 82 counties, 43 (52%) have reported WNV activity (positive animal, mosquito, or human cases). Human cases occurred among persons in 17 counties, with 20 (42%) cases reported from Hinds county, located in the most populated portion of the state. The attack rate for the state is 1.7 per 100,000 population, and that for Hinds county is 8.0.

Since May 1, 2002, MSDH has conducted active hospital-based surveillance, and this activity was responsible for identifying the incident human case with an onset date of June 24. Additional surveillance methods include dead bird reporting and testing, wild bird serosurveys, mosquito trapping and testing, and testing of sick equines. Testing of dead birds is limited to blue jays and crows; approximately 90% of the WNV-positive findings have been in blue jays. All mosquito pools that have tested positive for WNV were Culex quinquefasciatus.

Few local areas in the state conduct any type of mosquito control (i.e., surveillance, dipping, larvaciding, and adulticiding). To enhance mosquito-control activities in affected areas, MSDH and the Mosquito and Vector Control Association are sponsoring mosquito-control workshops for elected officials and public workers. The workshops are intended to provide training and technical assistance for public officials and workers responsible for mosquito control.

In addition to intensified mosquito-control efforts, response to the outbreak has included community awareness and education, including the launch of the Fight the Bite campaign to promote self-protection and source reduction; physician education; and enhanced surveillance in areas with human cases. Veterinarians have been encouraged to submit specimens from clinically ill equines for free testing by MSDH.

Additional information about MSDH WNV surveillance and prevention activities is available at http://www.msdh.state.ms.us. Additional information about WNV activity is available at http://www.cdc.gov/ncidod/dvbid/westnile/index.htm and http://www.cindi.usgs.gov/hazard/event/west_nile/west_nile.html.

Figure 1


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Figure 2


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