Specimen testing

All blood specimens were transported to CDC-DB in San Juan, Puerto Rico, on the day of collection, centrifuged, and serum was aliquoted and frozen at -80°C. Serum specimens were tested by anti-CHIKV IgM and IgG ELISA [29, 30]. Participants whose serum specimen tested positive by either assay were defined as “CHIKV-positive”; all other participants were defined as “CHIKV-negative”.

As previously described [22], mosquitos were collected from surveillance traps weekly, identified to species and sex, pooled into groups of ≤20 female Ae. aegypti, transported to CDC-DB, and frozen at -80°C. Pools were later homogenized, and RNA was extracted for testing by RT-PCR to detect CHIKV and DENV RNA [31]. During the second half of 2014, a total of 1,334 pools were tested that included 26,251 individual female mosquitos. As previously reported, no mosquito pools were positive for DENV [22, 32–34].