Chikungunya Virus Disease in Travelers – United States, 2010 – 2013 *

BACKGROUND: Chikungunya virus is a mosquito-borne alphavirus that can cause large outbreaks of acute febrile illness with severe polyarthralgia. It is an emerging health threat to the United States because humans are amplifying hosts and mosquito species that transmit the virus are present in many areas of the country. In late 2013, the first cases of locally-acquired chikungunya virus disease were identified in the Americas.

METHODS: We identified laboratory-confirmed chikungunya cases with diagnostic testing performed at the Centers for Disease Control and Prevention, the California Department of Public Health, or Focus Diagnostics from 2010‒2013. We defined a case as a patient with one of the following: 1) chikungunya virus or viral RNA detected by culture or RT-PCR; 2) ≥4-fold rise in anti-chikungunya virus neutralizing antibodies between acute- and convalescent-phase specimens; or 3) anti-chikungunya virus IgM antibodies with either anti-chikungunya virus IgG or neutralizing antibodies. Patients with chikungunya virus or RNA detected in serum were considered viremic. We described the epidemiology of these cases and determined which were reported to ArboNET, the national surveillance system for arboviral disease.

RESULTS: From 2010‒2013, 115 laboratory-confirmed chikungunya cases were identified in the United States. Sixty-seven cases were identified in 2010, 10 in 2011, 5 in 2012, and 33 in 2013. The median age of case-patients was 44 years [interquartile range (IQR) 34‒54 years]; only two case-patients were children. Travel history was available for 55 (48%) cases. Of those, 53 (96%) reported travel to Asia and 2 (4%) to Africa. The most commonly reported travel destinations were India (n=37), Indonesia (n=7), and the Philippines (n=7). Six patients were viremic after returning to the United States and an additional 15 patients returned <7 days after illness onset but did not have viral culture or RT-PCR testing performed. Of the 115 cases identified, only 24 (21%) were reported to ArboNET, with a median of 71 days (IQR 51–114 days) between illness onset and reporting.

CONCLUSIONS: Since 2010, a median of 22 chikungunya cases were identified per year in the United States. Although viremic travelers pose a theoretical risk for local transmission, no locally-acquired cases were identified. Less than one-quarter of recognized cases were reported to ArboNET; however, chikungunya is not currently a nationally notifiable condition. Given the recent increased risk of introduction into the United States, healthcare providers and public health officials should be educated about the recognition, diagnosis, and timely reporting of chikungunya cases.