PREVALENCE OF ANTIBODIES TO RICKETTSIAE LN THE HUMAN-POPULATION OF SUBURBAN BANGKOK

Following a report of three cases of scrub typhus in suburban Bangkok, we performed a serosurvey in the patients' communities. Both IgG and IgM antibodies were measured in an indirect immunoperoxidase assay, us ing separate spots of antigen from Rickettsia tsutsugamushi (scrub typ hus), R. typhi (murine typhus), and TT-118 spotted fever group rickett siae. Of 215 people donating blood, antibody levels indicative of most recent exposure to R. tsutsugamushi were most prevalent (21%), follow ed by R. typhi (8%), and TT-118 (4%). Seroprevalence suggesting most r ecent exposure to R. tsutsuga-mushi varied by location (range 13-31%), gender (26% of females and 13% of males), age (61-80-year-old individ uals were the highest, with a prevalence of 38%), and contact with orc hards and orchid farms (29% of those with extensive contact, 38% of th ose with occasional contact, and 10% of those with no contact). These patterns indicated that exposure to R. tsutsugamushi was related to oc cupation and behavior, as has been observed in areas of rural transmis sion. Expansion of metropolitan Bangkok has created a situation in whi ch people employed in agriculture live with people employed in the cit y. As a result, a serosurvey in suburban Bangkok reveals evidence of m urine typhus, which is usually transmitted in urban areas, as well as scrub and tick typhus, which are usually transmitted in rural areas.