¹Dept. of Health Sciences, The Hong Kong Polytechnic University, Hong Kong, ²Caritas Medical Centre, Hong Kong, ³Dept. of Microbiology, The University of Hong Kong

Verocytotoxigenic Escherichia coli (VTEC) causes diseases ranging from mild diarrhoea to haemorrhagic colitis to haemolytic uraemic syndrome in human. More than 57 serotypes have been described and O157:H7 is the most well-known serotype. Cattle are known to be the major reservoir for VTEC. The epidemiology of VTEC infections in Hong Kong has not been reported. Our study was to investigate the VTEC carriage rate in cattle and pigs from abattoir, to assess the contamination rate of carcasses during slaughter procedures and to study the incidence of VTEC infections in human. Faecal and carcass samples from 346 cows and 225 pigs were collected from Government Abattoir during the period 8/96 to 9/97. At the same time, faecal samples from 1003 patients suffering from diarrhoea were collected from 6 hospitals in Hong Kong. The samples were inoculated onto sorbitol MacConkey agar. For animal carcasses, an additional enrichment medium was used. Cultures were directly screened for VTEC by polymerase chain reaction (PCR). The primers used were degenerate-sequences MK1 and MK2 which allowed simultaneous amplification of verotoxin (VT) genes. VT-1, VT-2 and VT-2 variants. For each PCR positive sample, verocytotoxicity assays were done on 10 single colonies randomly selected for identity confirmation. VTEC strains were detected in faecal samples from 150 (43%) cows and 3(1.3%) pigs. Furthermore, they were also detected in carcass samples from 7 (2.1%) cows. Specific seasonal pattern of VTEC carriage in cows was not observed. For clinical cases, VTEC strains were detected in 4 (0.4%) patients. O157:H7 strains were identified from the faecal samples of I cow and 2 patients. By using DNA hybridization assay, it was found that majority of the animal VTEC isolates (66%) carried both verotoxin (VT-1 and -2) genes, 34% carried VT-2 gene alone, while none of the isolates carried VT-1 gene alone. For human VTEC isolates, 1 out of 4 (25%) carried both VT genes, while 3 out of 4 (75%) carried VT-2 gene alone. The specificity and simplicity of the PCR system used in this study make it a valuable alternative for rapid VTEC detection. VTEC carriage rate is high in cows, however, it is extremely low in pigs. Contamination of carcasses occurred at a very low level and this is attributed to the hygienic evisceration practised in the abattoir. Incidence of human VTEC infections in Hong Kong is also very low. O157:H7 is rare and VTEC strain with VT-1 gene alone is not found in this locality.