SEROEPIDEMIOLOGY OF LA-CROSSE VIRUS-INFECTION IN HUMANS IN WESTERN NORTH-CAROLINA

On the Cherokee Indian Reservation and surrounding area of western Nor th Carolina, an area-wide serosurvey was conducted to determine the pr evalence of neutralizing antibody to La Crosse (LAG) virus. A question naire was used to identify risk factors important in exposure to virus -infected mosquitoes in populations near the reservation. Of 1,008 ser um samples tested, 9.6% were positive for LAC virus antibody. For samp les solely collected from on (n = 311) or off (n = 697) the reservatio n, the prevalence of seropositive samples was 20.6% on the reservation and only 4.7% off the reservation. Seropositivity increased directly with age, indicating that transmission of LAC virus was highly endemic . Age and location residence (on versus off the reservation) were sign ificant risk factors for exposure to LAC virus. Persons on the reserva tion were 5.5 times more likely to have been exposed to LAC virus than were people who reside off the reservation. An additive increase in r isk of 1.5 times over each age group was found, so that the oldest age group (greater than or equal to 75 years) was 7.5 times more likely t o have been exposed to LAC virus than was the youngest age group (< 1- 14 years).