Vibrio cholerae El Tor Inaba Outbreak in Khonkaen Province, July – September 2010

Abstract

Background: On 11^th August 2010, Bureau of Epidemiology (BOE) was notified about 14 cases of Vibrio cholerae Inaba in Muang district, Khonkaen province. BOE team conducted investigation with Khonkaen SRRT team and the Office of Disease Prevention and Control 6th to identify source and risk factors of the outbreak.
Methods: We reviewed medical records and case investigation of cholera cases in hospital, interviewed all available cases and food handlers. Confirmed case was defined as a person who had loose or watery stool, had onset from 30th July – 16th September 2010 and lived in Khonkaen province with rectal swab culture positive for Vibrio cholerae O1 eltor Inaba. Probable cases were the people who met case definition and consumed suspected food with the confirmed case of VC Inaba. We conducted a case control study. The case was confirmed and probable case who had age ≥ 15 years. Control was a person who lived near case’s house and no clinical diarrhea 2 weeks before and after onset of case. Case to control ratio was 1 to 2. We sent specimens from foods, water, environment swab and RSC for culture VC. We surveyed markets, waste water treatment system and suspected food shops.
Results: During this period, there were 44 confirmed, 5 probable cases. Most cases were reported from Muang district and few were from Banpai and Banhad. There were 16 hospitalized cases (5 hypovolumic shock). Male to female ratio was 1 to 1.45. Median age was 36 years old with IQR from 19 to 50 years old. Investigation of clusters and cases suggested different food items from A. market and B. market as main sources of the first few months of this outbreak. The later period of the outbreak linked with raw small shrimps salad consumption that the shrimps came from a canal connected to waste water treatment system. Result of case control study showed increase risk among people who ate outside or buy ready-to-eat foods (adjusted OR = 4.42, 95% CI = 1.36 – 14.39) and history of raw meat consumption (adjusted OR = 4.45, 95% CI = 1.23 – 16.14). For laboratory result, all were negative for cholera culture except waste water in main canal and the connected canal. Environment survey in A. market and B. market reveal poor sanitation and no chlorine in the water used for public toilet of B. market.
Conclusions: This prolong outbreak related with contamination of various foods in 2 main markets of Muang district. In the later period of the outbreak, source was shift to canal that connects to waste water drainage area. People who ate outside or buy food for eating and those who ate raw meat were the high risk group of this outbreak.