Verocytotoxin- producing Escherichia coli 0157 on a farm open to the public: outbreak investigation and longitudinal bacteriological study
- G. C. Pritchard, BVM&S,BSc, DVM&S, FRCVS1,
- T. Carson, HNC1,
- G. A. Willshaw, BSc, PhD2,
- T. Cheasty, BSc2 and
- J. R. Bailey, MB, BS,MFPHM3
- 1 Veterinary Laboratories Agency - Bury St Edmunds, Rougham Hill, Bury St Edmunds, Suffolk IP33 2RX
- 2 Laboratory of Enteric Pathogens, Division of Gastrointestinal Infections, PHLS Central Public Health Laboratory, 61 Colindale Avenue, London NW9 5HT
- 3 Norfolk Heath Authority, St Andrews House North Side, Thorpe St Andrew, Norwich, Norfolk NR7 OHT
Verocytotoxin-producing Escherichia coli (vTEC) 0157 phage type 2 (PT2) was isolated from three calves and two goats on a farm open to the public. Phenotypic and DNA-based typing showed that the strains were identical or very closely related to those obtained from an outbreak of VTEC 0157 infection in two separate family groups who visited the farm. No VTEC 0157 PT2 was isolated again from the farm during a 12-month longitudinal bacteriological study undertaken after the infected animals had been removed. However, phenotypically and genotypically indistinguishable VTEC 0157 PT21/28 strains were detected in two of 474 faecal samples collected at monthly visits from 15 species of animals of various ages. The two isolates were obtained from calves from different sources sampled 146 days apart, suggesting that the infection had persisted on the farm although it was not detected in the other species. The same strain was subsequently isolated from another calf housed in the same pen as one of the infected calves. The longest period during which the organism was excreted was seven days. No VTEC 0157 was isolated either from 204 replacement animals (including 138 orphan lambs and 10 calves) brought in from various sources, and sampled while they were kept in isolation for two weeks before being introduced to the farm, or from environmental samples. During the study a visitor became ill with VTEC 0157 PT2. However, the isolate was distinct from those recovered from the farm and there was no evidence to suggest that the visit was the source of the infection.
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