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BACKGROUND: During 2014, chikungunya virus (CHIKV) quickly spread throughout the Americas to many areas that are also endemic for dengue virus (DENV). Both can be spread by the same mosquito species, and in the past co-infections have been identified in areas endemic to both viruses. Florida had high numbers of imported CHIKV and DENV fever cases in 2014, all of which were in people with recent travel history to areas affected by either or both viruses.
METHODS: Data from Florida Department of Health Merlin reporting system were used to compare reported cases of chikungunya fever (CHIK) and dengue fever (DEN) to identify any individuals that may have experienced co-infections. National case definition criteria were used to classify cases. Both CHIKV and DENV testing is performed at the Bureau of Public Health laboratories (BPHL). Samples forwarded to the BPHL for confirmatory testing for DENV or CHIKV are tested for both viruses.
RESULTS: As of March 1, 2015, 507 cases of imported CHIK and 88 cases of imported DEN were reported in Florida with onset from January 1, 2014 to January 27, 2015. Twenty persons were reported as both DEN and CHIK cases. Five cases had concurrent infections, evidenced by positive polymerase chain reaction (PCR) results for both viruses. Seven were PCR positive for one virus and IgM positive for the other, indicating potential consecutive infections. Of these cases, only two could definitively report different onset dates for their infections. The remaining eight cases were IgM positive for both viruses and reported a single onset date, indicating recent infections with undetermined co-infection status. Cases with both CHIKV and DENV infections had travel history to Cuba (7), Dominican Republic, Haiti (3), Honduras (2), India, Jamaica (3), Mexico, and Puerto Rico (2). Most cases were visiting friends/relatives (80%) and spent an average of 24 days outside of Florida. Those with multiple infections presented with fever (100%), myalgia (80%), thrombocytopenia (80%), arthralgia (75%), retro-orbital pain/headache (75%), rash (45%), leukopenia (30%), nausea/vomiting (25%), and diarrhea (20%).
CONCLUSIONS: Providers should consider both DEN and CHIK when evaluating suspect cases with travel to areas where both viruses are present. The BPHL identified 80% of co-infections, highlighting the value of public health confirmation of specimens. The low number of patients reporting two distinct onset dates suggests dual, immediately consecutive, or asymptomatic secondary infections. Co-infections are most likely underreported due to incomplete testing, asymptomatic infections, and not all infected individuals seeking healthcare.