PREVALENCE OF ANTIBODIES TO MOSQUITO-BORNE ENCEPHALITIS VIRUSES IN RESIDENTS OF THE COACHELLA VALLEY, CALIFORNIA

Sera from 19 (2.6%) and 118 (16.4%) of 719 outpatients attending clini cs in the southeastern Coachella Valley, California during 1993 and 19 94 exhibited IgG antibodies to western equine encephalomyelitis and St . Louis encephalitis (SLE) viruses, respectively, using enzyme immunoa ssays. However, only seven (1.0%) and 36 (5.0%) outpatients were posit ive by plaque-reduction neutralization tests (PRNTs), and seven (1.0%) and 84 (11.7%) outpatients were positive by sera hemagglutination inh ibition assays, respectively. None were positive for IgM antibodies in dicative of recent infection or were diagnosed clinically with central nervous system disease. Prevalence of PRNT antibody to SLE increased as a function of patient age, but did not vary significantly in relati on to years of residence, sex, race, postal zip code, occupation, or m onth of collection.