An investigation of chikungunya outbreak, Suphan Buri, Thailand, April–October 2020

Abstract

Background: Division of Epidemiology received a notification from Suphan Buri Provincial Public Health Office that more than 300 suspected chikungunya cases were found. The joint investigation team conducted an investigation during 3–7 August to verify diagnosis and confirm the outbreak, describe epidemiological characteristics of the outbreak, assess gaps in surveillance and control measure in clinics/drugstores & village health volunteers (VHVs), and provide recommendations.
Methods: We reviewed R506 and medical records. Active case finding was performed. We defined a suspected case as any person with fever and joint pain with at least one of the following symptoms: myalgia, maculopapular rash, headache, and retro–orbital pain. Confirmed case was any person who tested positive for chikungunya virus by RT–PCR. Positive samples were sequenced. We calculated household attack rate. We did an environmental survey, larvae survey, investigate a parous rate, and interviewed VHVs, clinic/drugstore owners about ad hoc surveillance and control measures.
Result: There was chikungunya outbreak in Suphan Buri with total of 670 cases during 1 April–5 October 2020. Fifty-three percent were female. The most attack rate was found among 10–14 years (189 cases per 100,000 population). Danchang district had the highest attack rate (764 cases per 100,000 population). Fifty-five percent of cases sought medical attention at clinic/drugstore and 42% of patients’ households (>=2 people/household) had attack rate 75–100%. Chikungunya genotype was ECSA strain with no mutation. After intensive implementation of control measures for 28 days in the epidemic area, number of new cases and House Index/Container Index decreased. Sixty-five percent of VHV used temephos improperly and 65% of clinic/drugstore didn’t aware of the ad hoc surveillance set up during the outbreak.
Conclusion: The first large chikungunya outbreak in Suphan Buri was confirmed and had the fifth–highest attack rate in Thailand. Children/teenage was most affected. The household attack rate was more than 75 percent. Over half of cases sought medical attention at clinics/drugstores so implementing the ad hoc surveillance in clinics/drugstores during the outbreak should be strengthened. Proper temephos using should be redemonstrated to VHVs and evaluated especially before the rainy season.