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Human Arboviral Encephalitis -- United States, 1983

In 1983, 105 cases of arboviral encephalitis were reported in the United States (Figures 2 and 3). Brief reports follow.

St. Louis encephalitis (SLE): In the central United States, where epidemic Culex pipiens-borne SLE was expected, remarkably few cases were reported: two occurred in Cook County, Illinois, and one, in Jackson County, Indiana. Sporadic cases were documented in a Florida man who traveled widely in the month before onset of illness and in residents of El Paso County, Texas, and Bernalillo County, New Mexico.

An outbreak of Cx. tarsalis-borne SLE occurred in California and Arizona in association with flooding of the lower Colorado River. The estimated attack rate for California residents of census subdivisions contiguous with the river in Riverside, Imperial, and San Bernadino Counties was 4/25,928 (15.4/100,000). Two residents of other California counties visited flooded sections of the Colorado River in the 2 weeks before their onsets of illness and also may have been infected there. Five SLE cases occurred among Arizona residents, but exposures of only three were temporally and geographically associated with Colorado River flooding. The estimated attack rate for Arizona census subdivisions adjoining the river was 3/130,107 (2.3/100,000). Although the reasons for a lower attack rate in Arizona are unclear, a larger urban population (removed from exposure to Cx. tarsalis) in areas of risk in Arizona may have been a contributing factor.

Contrary to observations in California's central valley in the 1940s and 1950s, nine of the 14 cases in California and Arizona in 1983 occurred among adults 50 years of age or older (Figure 4). The increased number of cases among adults may reflect a decline in endemic transmission with age during the past 30 years, resulting in an increase in susceptibility.

Eastern equine encephalitis (EEE): Fourteen EEE cases occurred in 1983. Increased transmission of EEE virus in Massachusetts' Taunton Valley led to six human cases. In Rhode Island, where EEE was reported in humans for the first time, two cases occurred.

Other human cases occurred in recognized endemic foci of EEE virus activity: Onondaga County, New York; Lowndes County, Georgia; Elkhart County, Indiana; and several Florida counties.

The overall case-fatality ratio was 35.7% (five deaths among 14 cases). A trend was observed toward greater mortality among males--57.1%, compared with 14.3% among females (p = 0.13) (Figure 3).

Western equine encephalitis (WEE): An outbreak of WEE led to six human cases in geographically disparate areas of Minnesota, North Dakota, and South Dakota. Although no fatalities occurred, two infants sustained residual neurologic damage. All cases occurred among males, and all but one, among children (Figure 3). A single WEE case occurred in a 45-year-old Hale County, Texas, man.

California encephalitis (CE): Sixty-four CE cases were reported primarily among residents of states bordering the Great Lakes. The disease occurred focally in southeastern Minnesota counties and adjacent western counties in Wisconsin. A greater proportion of cases from Minnesota and Wisconsin occurred late in the summer--13 of 25 patients from these states and 10 of 39 patients from other states had onset after September 1 (X((1)) = 4.60 p 0.05). Forty-three cases (67%) occurred among males (Figure 3), and 50 cases (78%) occurred among children 0-10 years of age. The geographic, temporal, age, and sex distributions of cases in 1983 were similar to observations in other years. Reported by LH Lauerman, DVM, Alabama Dept of Agriculture and Industries, WE Birch, DVM, State Epidemiologist, Alabama Dept of Public Health; H Webster, MD, W Stromberg, PhD, ME Wright, J Doll, PhD, NJ Petersen, SM, State Epidemiologist, Arizona Dept of Health Svcs; JP Lofgren MD, State Epidemiologist, Arkansas Dept of Health; R Emmons, MD, R Murray, MD, R Roberto, MD, J Chin, MD, State Epidemiologist, California State Dept of Health Svcs; JK Emerson, DVM, SW Ferguson, PhD, State Epidemiologist, Colorado State Dept of Health; A Main, PhD, R Shope, MD, Yale Arbovirus Research Unit, New Haven, MA Markowski, EE Jones, MD, State Epidemiologist, Connecticut State Dept of Health Svcs; PR Silverman, DrPH, State Epidemiologist, Delaware Dept of Health and Social Svcs; HL Rubin, DVM, Florida Dept of Agriculture and Consumer Svcs, F Sorhage, MD, W Bigler, PhD, JJ Sacks, MD, Acting State Epidemiologist, Florida State Dept of Health and Rehabilitative Svcs; J Cole, DVM, Universtiy of Georgia, Tifton, RK Sikes, DVM, State Epidemiologist, Georgia Dept of Human Resources; HJ Dominick, Pesticides and Vector Control, W Turnock, MD, Chicago Dept of Health, RJ Martin, DVM, C Langkop, MD, BJ Francis, MD, State Epidemiologist, Illinois State Dept of Public Health; M Sinsko, PhD, CL Barrett, MD, State Epidemiologist, Indiana State Board of Health; D Dorsey, PhD, LA Wintermeyer, MD, State Epidemiologist, Iowa Dept of Health; DE Wilcox, MD, State Epidemiologist, Kansas State Dept of Health and Environment; JC McCammon, Louisville and Jefferson County Dept of Health, MW Hinds, MD, State Epidemiologist, Kentucky State Cabinet for Human Resources; W Atkinson, MD, HB Bradford, Jr, PhD, L McFarland, DrPH, CT Caraway, DVM, State Epidemiologist, Louisiana State Dept of Health and Human Resources; CP Lazar, MD, G Stern, DVM, Maryland Dept of Agriculture, E Israel, MD, State Epidemiologist, Maryland State Dept of Health and Mental Hygiene; V Berardi, H Maxfield, NJ Fiumara, MD, State Epidemiologist, Massachusetts State Dept of Public Health; H McGee, MPH, KR Wilcox, MD, State Epidemiologist, Michigan State Dept of Public Health; L Boyd, PhD, MT Osterholm, PhD, AG Dean, MD, State Epidemiologist, Minnesota State Dept of Health; DL Sykes, QA Long, Gulf Coast Mosquito Control Commission, Gulfport, FE Thompson, MD, State Epidemiologist, Mississippi State Board of Health; HD Donnell, Jr, MD, State Epidemiologist, Missouri State Dept of Social Svcs; JK Gedrose, State Epidemiologist, Montana State Dept of Health and Environmental Sciences; PA Stoesz, MD, State Epidemiologist, Nebraska State Dept of Health; WJ Crans, PhD, New Jersey Agricultural Experiment Station, New Brunswick, WE Parkin, DVM, State Epidemiologist, New Jersey State Dept of Health; J Montes, HF Hull, MD, Acting State Epidemiologist, New Mexico Health and Environment Dept; M Grayson, PhD, R Deibel, MD, DL Morse, MD, R Rothenberg, MD, State Epidemiologist, New York State Dept of Health; JN MacCormack, MD, State Epidemiologist, North Carolina Dept of Human Resources; K Tardiff, JL Pearson, DrPH, State Epidemiologist, North Dakota State Dept of Health; ED Peterson, M Parsons, MS, TJ Halpin, MD, State Epidemiologist, Ohio State Dept of Health; E Witte, DVM, CW Hays, MD, State Epidemiologist, Pennsylvania State Dept of Health; SG Morin, Rhode Island Dept of Environmental Management, RA Keenlyside, MBBS, State Epidemiologist, Rhode Island State Dept of Health; KA Senger, State Epidemiologist, South Dakota Dept of Health; JG Hamm, SJ Jones, JR Oates, WP Kelly, Memphis-Shelby County Health Dept, RH Hutcheson, Jr, MD, State Epidemiologist, Tennessee State Dept of Public Health; JW Flosi, PhD, G Hunt, PhD, Harris County Mosquito Control District, RL Johns, PhD, C Reed, MPH, CE Alexander, MD, State Epidemiologist, Texas State Dept of Health; C Nichols, MPH, RE Johns, Jr, MD, State Epidemiologist, Utah Dept of Health; GB Miller, Jr, MD, State Epidemiologist, Virginia Dept of Health; JM Kobayashi, MD, State Epidemiologist, Washington State Dept of Social and Health Svcs; JP Davis, MD, State Epidemiologist, Wisconsin State Dept of Health and Social Svcs; J Pearson, DVM, National Veterinary Svcs Laboratory, US Dept of Agriculture, Ames, Iowa; Div of Vector-Borne Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Active surveillance of encephalitis caused by SLE, EEE, WEE, and California serogroup viruses is maintained at CDC by periodic telephone contact with state health departments and laboratories during the spring and summer months. Active surveillance is supplemented with the following passive systems: review of encephalitis case reports submitted to CDC by health departments and identification of arboviral encephalitis cases diagnosed in CDC's Arbovirus Reference Branch from unsolicited specimens.

The diagnosis of arboviral encephalitis is confirmed if virus is isolated from the patient or a fourfold or greater rise or fall in antibody titer is documented. The recent introduction of immunoglobulin M-capture, enzyme-linked immunosorbent assays for the diagnosis of EEE, WEE, SLE, and LaCrosse encephalitis has made possible specific diagnoses using cerebrospinal fluid or serum obtained during the acute phase of illness. These techniques are currently in use in CDC's Arbovirus Reference Branch.

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