A study on epidemiological characteristics and control methods of EHEC infection in Korea

Lee, Sang Won; Lee, Bok Kwon; Lee, Yong Jae; Lee, Hee Soo; Jung, Suk Chan; Sun, Kwak Hyo; Choi, Bo Youl

Abstract

E. coli is a bacterium that is commonly found in the gut of humans and warm-blooded animals. Most strains of E. coli are harmless. But some strains such as Enterohaemorrhagic E. coli(EHEC), can cause severe food borne disease. It is transmitted to humans primarily through consumption of contaminated foods, such as raw or undercooked ground meat. There is no widely agreed definition of when a shiga-toxin producing E. coli is considered to be an EHEC. But in Korea, the word "EHEC", "STEC", "VTEC" are often used as same meaning, which refer to the E.coli those producing shiga-toxin. We suggest the term STEC refers to those E. coli produce one or more shiga-toxins(stx), and the term EHEC refers only to STEC that cause a clinical illness. EHEC infection were designated as the class 1 notifiable disease in Korea in 2000. Although EHEC/STEC cases were not common in Korea, the number of STEC infection cases reported has increased since 2001. From 2001 to 2004, the number of STEC infection cases in Korea were 11, 8, 52, 118 respectively. These cases included 17 due to E. coli O157, 136 due to E. coli, serogroup non-O157, and 15 due to E. coli that were not serogrouped. The most common serotype implicated is E. coli O91 without virulent factor and clinical symptoms. But those cases involve in one epidemic in primary school in 2004. STEC infections in Korea occur in all age groups, with the highest frequencies in children less than 5 years old. Healthy cattle are the main animal reservoir for STEC and they harbor the organism as part of the bowel flora. The proportion of STEC in E. coli in animal feces was examined by using stool samples from 283 Korean beef cattle on 27 farms, 169 milk cattle on 28 frams, 455 swine on 50 farms. As determined by culture and toxin assay, the proportion of STEC was 25.8%(16 STEC/62 E. coli) in milk cattle, 18.8%(19 STEC/101 E.coli) in Korean beef cattle, 14.0%(25 STEC/178 E. coli) in swine. Effective surveillance of EHEC/STEC in humans is essential in order to protect the public health. EHEC infection is notifiable in many countries including USA, Japan, and Belgium, Finland, Italy, Netherlands, and the United Kingdom(UK), have sentinel systems. England, Wales, and Scotland have comprehensive national laboratory reporting schemes for STEC. And there has been an increase in the number of reported cases and outbreaks during the past decades in many countries Prevention of STEC infection requires control measures at all stages of surveillace, investigations and special pathogen tracing such as PulseNet.