Epidemiological investigation of chikungunya outbreak, West Kalimantan, Indonesia

Background: Chikungunya is a vector-borne infection with high morbidity rate and associated with debilitating
prolonged polyarthritis and substantial socioeconomic impact. On 4 January 2010, a chikungunya outbreak was
reported in Sukadana Subdistrict, West Kalimantan, Indonesia.
Objective: An epidemiological investigation was conducted to identify the risk factors for the outbreak and recommend
control measures.
Method: A case-control study was conducted to identify the risk factors of the outbreak. The cases were residents
who had major clinical symptoms of chikungunya that were identified by active case finding through the affected
area while controls were neighbor of the cases. Interviews were conducted to collect demographic and
clinical data as well as the risk factors of infection. The venous blood from ten patients, selected randomly, were
collected and tested for diagnosis confirmation.
Results: During 12 December 2009 and 10 January 2010, a total of 65 chikungunya cases were identified with no
death. Seven out of ten blood samples were confirmed as chikungunya cases. All of the patients had fever, rash
and arthralgia while headache was reported in 43% of the cases. The attack rate was 17.3% (range 3.9–22.6%)
and those aged>44 year old had the highest attack rate. In multivariate model, those farming in the forest and
those who had poor practices in eliminating mosquito breeding sites had higher odds of having chikungunya,
with adjusted OR: 10.66 (95%CI: 3.95–28.79) and adjusted OR: 3.51 (95%CI: 1.35–9.13), respectively.
Conclusions: Farming in the forest and poor vectors control are two risk factor of chikungunya infection.
Therefore, using anti-mosquito repellent when farming and continuous and coordinated mosquito breeding sites
elimination are recommended.