Emergence of Locally-Acquired Chikungunya in Florida

BACKGROUND: Chikungunya fever is transmitted through Chikungunya virus infected Aedes aegypti and albopictus mosquito bites. Symptoms include fever, joint pain, and rash. The disease is rarely fatal, but can cause temporary disability. Chikungunya virus (CHIKV) was introduced into the Caribbean in late 2013. Five locally acquired infections have been reported in Florida since July 17, 2014.

METHODS: Infections with CHIKV were identified through active and passive surveillance. Travel history, onset of illness, symptoms, and risk factors for infection were gathered. A locally-acquired Chikungunya case was defined as an individual who had laboratory evidence of Chikungunya infection (by RT-PCR or ELISA), residence in Palm Beach County (PBC) during illness onset, and no recent history of travel outside PBC. Home isolation of case-patients during viremic phase was implemented. Mosquito Control was notified to complete an environmental assessment and treatment around the case-patients home. A field investigation was conducted within 100 meters of each case-patient’s home. The objectives of the field investigation were to identify and test symptomatic and asymptomatic persons, evaluate risk factors, conduct environmental assessment and provide recommendations to eliminate mosquito breeding sites. Following identification of the second locally acquired case-patient, testing was targeted to only symptomatic persons.

RESULTS: Through active surveillance, three locally-acquired case-patients were identified between July 17 and August 13, 2014. There was no clear epidemiological link established through geo-spatial relationships during incubation and infective periods among imported and or locally-acquired case-patients. During three separate field investigations on 7/24/2014 through 8/9/2014, 78 households were visited, of which six were vacant and no one was home at the other 28. No symptomatic persons were identified. All eight blood samples obtained tested negative for CHIKV. The field teams identified mosquito breeding sites on some properties and drained and covered the stagnant water. Education on preventing further mosquito-borne illness was shared verbally and through printed materials provided to every household.

CONCLUSIONS: This investigation did not find any evidence to suggest that further local transmission had occurred. Isolation of cases-patients during the viremic phase likely prevented transmission among household members and local community members.