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Current Trends Human Arboviral Encephalitis -- United States, 1982

In 1982, 185 laboratory-confirmed cases of human arboviral encephalitis* were reported from 23 states (Figure 2); at least four cases were fatal. This is a 48% increase from the 125 cases reported in 1981, but is far below the peak of 2,113 cases reported in 1975 (Table 1).

California encephalitis (CE) accounted for 130 (70%) of all encephalitis cases. Ohio reported the greatest number, 37, followed by Wisconsin with 29. No fatalities were reported. CE cases were concentrated in the eastern United States, with most occurring in the Great Lakes area. Jamestown Canyon virus, a member of the CE virus complex, was confirmed by the New York State Laboratories as the etiologic agent producing encephalitis in an elderly population.

St. Louis encephalitis (SLE) virus, which caused 34 (18%) cases, was the second most commonly occurring etiologic agent. Most SLE cases were reported from Texas (14), Mississippi (eight), and Louisiana (four); Illinois and the southeastern states reported the others. At least two cases were fatal, but information on the clinical results of eight cases is not yet available.

Five states reported 12 eastern equine encephalitis (EEE) cases; two (17%)--one each in Florida and Georgia--were fatal. The largest number of cases (four) occurred in Georgia, and these were concentrated in the southern part of the state.

Nine cases of western equine encephalitis were reported during 1982, all in the western United States, and no fatalities were reported. Texas reported the largest number of cases (four).

Temporal distribution of encephalitis cases for which onset dates were provided is shown in Figure 3. Most cases (86%) occurred from July through September; no cases with onset after October have been reported. These data are consistent with periods of peak vector density. Age and sex distribution of encephalitis patients in 1982 were typical of previous years, with SLE and EEE cases occurring in the young and elderly age groups, CE cases affecting mainly young age groups, and males (64%) affected more frequently by all types than females (Table 2).

A major epizootic of EEE involving pheasants, quail, and several hundred horses occurred on the East and Gulf coasts during the summer months. Reported WEE cases in horses were sporadic in the west. Reported by Div of Vector-Borne Viral Diseases, Center for Infectious Diseases, CDC.

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