Chikungunya Outbreak, Singapore, 2008

a 1972 serosurvey suggested widespread distribution of chikungunya infection , and numerous outbreaks have reemerged since 2001 (3). Malaysia reported its fi rst outbreak between De-cember1998 and February 1999 and a reemergence in an isolated northwestern coastal town in 2006 (4). In Singapore, although dengue fever has been endemic since the 1960s, the fi rst chikungunya case was not reported until 2006. In 2007, 10 imported cases were reported to Singa-pore's Ministry of Health (5). Notably, Taiwan reported a case involving a returning student from Singapore in November 2006, suggesting the possibility of autochthonous transmission in Singapore (6). Located in tropical Southeast Asia, Singapore has remained vigilant in the surveillance of chikungunya. A 2002/2003 serosurvey on 531 healthy young adults showed only 2 (0.3%) persons with chikungunya antibodies (7). We describe an outbreak of au-tochthonous chikungunya transmission in Singapore and discuss removal of infectious human reservoirs from transmission areas as an outbreak control strategy. On January 14, 2008, a local case of chikungunya infection was detected through the general practitioners' laboratory-based surveillance system established by Singapore's Environmental Health Institute in 2006. The Ministry of Health responded with a massive active surveillance exercise. A total of 2,626 people who resided or worked within a 150-m radius of the index case-patient's address were screened for chikungunya infection by reverse transcription–PCR (RT-PCR), using primers adapted from Hasebe et al. (5,8). Persons with an acute febrile illness, signs or symptoms compatible with chikungunya fever (fever, joint pain, or rash), or those with positive RT-PCR results were referred to the Communicable Disease Centre at Tan Tock Seng Hospital (CDC/TTSH), the national infectious disease referral center in Singapore.kungunya infection was confi rmed for 13 patients (5). Of these, 10 acutely symptomatic patients (all men; median age 35 years, range 22–69 years) were isolated at CDC/TTSH until fever resolved and a negative chikungu-nya RT-PCR test result was obtained. During hospitalization, patients' temperatures were monitored every 4 hours and daily chikungunya RT-PCR tests were performed. Viral load pro-fi les were derived from an external standard curve generated by 10-fold serially diluted virus from a concentration of 10 8 pfu/mL, using crossing-point values. The Table summarizes the presence of viremia and patients' febrile status in relation to the day of illness. High levels of viremia were observed during the fi rst 5 days of illness (median 119,126 pfu/mL, range 360– 14,605,314 pfu/mL). Fever lasted a median of 5 days …