How to explain the re-emergence of chikungunya infection in Reunion Island in 2010?

In March 2010, a new outbreak of chikungunya infection was detected in the west of Reunion Island. An investigation was launched to describe the incident cases occurrence and to raise hypotheses on factors that could explain the occurrence of this outbreak. All probable or confirmed cases detected by the surveillance system in the western area between March 1st and July 2nd, 2010 were included in the investigation. A standardized questionnaire was performed by phone, including sociodemographic, environmental and behaviour data. A total of 74 cases were described (i.e. response rate of 72%). They were mainly women (sex ratio M/F=0.7), all ages were represented. Most of them (76%) resided in a house; 31% had recently moved, including 22% from metropolitan France. They reported to have been more exposed to mosquitoes and to infected patients than during the major epidemic of 2005-2006. In addition, 41% reported to have reduced their protection against mosquitoes. The results suggest that several concomitant factors contributed to this outbreak: the reintroduction of the chikungunya virus in the island, the population characteristics and environmental factors.