To the Editor: Chikungunya virus (CHIKV) first emerged in Indian Ocean islands off the eastern coast of Africa in 2005 and was responsible for large-scale epidemics on the islands of Reunion, Comoros, Mayotte, Mauritius, Madagascar, and Seychelles (1-4). On Reunion Island, a French overseas territory of 810,000 inhabitants, herd immunity reached 38% in October 2006 (5). Molecular epidemiology of the strain responsible for these outbreaks indicated that it had originated in Kenya (6). The epidemic on Reunion Island was associated with a mutation in the envelope protein gene (E1-A226V) that improves replication and transmission efficiency in Aedes albopictus mosquitoes (7).
Since 2006, the Regional Office of the French Institute for Public Health Surveillance in the Indian Ocean has conducted epidemiologic and biological surveillance for CHIKV infection. Case definitions have been described (8). During December 2006-July 2009, no confirmed case was detected on Reunion Island and Mayotte, but new outbreaks were reported in Madagascar (9). In August 2009, a cluster of cases was identified on the western coast of Reunion Island (8).
We report an outbreak of CHIKV infection that occurred on Reunion Island in 2010. The first case was detected on March 17, 2010. As of July 6, a total of 100 confirmed and 32 probable cases had been identified (online Appendix Figure, www. cdc.gov/EID/content/17/2/307-appF. htm). Median age of case-patients was 39 years (range 6 months-80 years), and the ratio of male to female casepatients was 0.81:1. In addition to fever (95%), case-patients had arthralgia (95%), headache (78%), and myalgia (75%). Seven (5%) were admitted to hospitals. No severe illness or death was reported. The outbreak remained largely restricted to residents of Saint Paul (75%) on the western coast. Sporadic cases in other cities also were detected.
Sequence comparison based on partial envelope gene or complete genome showed a high level (>99.6%) of nucleotide and amino acid identity of 2010 isolates from Reunion Island with...