Epidemiological surveillance du chikungunya on Reunion Island from 2005 to 2011

INTRODUCTION: The largest chikungunya epidemic in history hit Reunion Island in 2005/6. At that time, a specific monitoring system was set up. Since the end of the epidemic, this monitoring system has continued to operate and has been enhanced. The main objectives of the system are early detection of any case of chikungunya virus infection and epidemiological monitoring. METHODS: During nonepidemic periods, surveillance is focused on active detection of all cases. During epidemic periods, weekly incidence is estimated using data collected via a sentinel physician network. Occurrence of severe and fatal forms is tracked during all epidemiologic situations. RESULTS: In 2005-2006, the estimated number of symptomatic chikungunya-virus infections diagnosed on Reunion Island was 266 000, i.e., an attack rate of 34%. A total of 222 severe cases and 44 mother-to-child transmissions were recorded. Since the end of the outbreak, two clusters have been detected in the western region of the island in 2010 and 2011. The second cluster was non-negligible since it involved 164 cases including 112 that were biologically confirmed. CONCLUSION: Based on results recorded from 2005 to 2006, the chikungunya monitoring system appears to have good sensitivity and reactivity. Recent detection of two disease clusters confirms the system's efficacy.