Prevalence of enterohemorrhagic Escherichia coli O157:H7 in a survey of dairy herds

Abstract

The prevalence of Escherichia coli O157:H7 in dairy herds is poorly understood, even though young dairy animals have been reported to be a host. From February to May 1993, 662 fecal samples from 50 control herds in 14 states, and from June to August 1993, 303 fecal samples from 14 case herds in 11 states were collected for isolation of E. coli O157:H7. Case herds were those in which E. coli O157:H7 was isolated from preweaned calves in a previous U.S. Department of Agriculture study, whereas control herds from which E. coli O157:H7 had not been isolated previously were randomly selected from the same states as case herds. Among the control herds, E. coli O157:H7 was isolated from 6 of 399 calves (1.5%) that were between 24 h old and the age of weaning and from 13 of 263 calves (4.9%) that were between the ages of weaning and 4 months. Eleven of 50 control herds (22%) were positive. Among the case herds, E. coli O157:H7 was isolated from 5 of 171 calves (2.9%) that were between 24 h old and the age of weaning and from 7 of 132 calves (5.3%) that were between the ages of weaning and 4 months. Seven of 14 case herds (50%) were positive. Sixteen of 31 isolates were obtained by direct plating, with populations ranging from 10 3 to 10 5 CFU/g. Fifteen of 31 isolates were isolated by enrichment only. Nineteen of the isolates produced both verocytotoxin 1 (VT-1) and VT-2, whereas 12 produced VT-2 only.

Risk Factors for the Presence of High-Level Shedders ofEscherichia coliO157 on Scottish Farms

“…From weaning until 12 months of age, calves are believed to be a major risk group for shedding VTEC O157 (18,39,43). Higher prevalences have been detected for calves after weaning (11,16,56). Studies conducted in other countries have reported similar E. coli O157 excretion rates for calves but with higher prevalences for weaned calves than for unweaned calves (11).…”

Manure and Microbes: Public and Animal Health Problem?

“…This organism is of concern to the dairy industry because many outbreaks have been traced to ground beef and some to raw milk (7, 18) as well as to water, apple cider ( 1 ) , and vegetables (56). Dairy farms have been identified as reservoirs of E. coli O157:H7 (22,57,60). It was suggested, but not proven, that the apples that were the source of the E. coli O157:H7 in the Massachusetts cider outbreak had been contaminated by manure that had been deposited under the trees ( 1 ) .…”

“…Research on E. coli O157:H7 in dairy cattle from Washington (22), Wisconsin and Washington ( 5 7 ) and two national US studies (20,60) indicate that the prevalence of this bacterium is less than 5% and usually lower than 1%. It is difficult to compare these studies because different detection methods of varying sensitivities, sample collection strategies, age grouping, and number of samples collected were used.…”

“…Recovery of E. coli O157:H7 was three times more likely on the case farms than on the control farms. Samples were collected from 64 and 50 control herds in 14 states in the national studies, one of which was conducted in 1991 to 1992 ( 2 0 ) and the follow-up study that took place in 1993 to 1994 (60). In addition, 3 case herds were sampled from the first study and 14 case herds were sampled from the second study in which E. coli O157:H7 had been identified.…”

Modelling the vector pathway and infection of humans in an environmental outbreak of Escherichia coli O157

“…In addition, 31% of sheep excreted E. coli O157 during summer time [7] and 2.9% of UK lamb [8] products were contaminated with the pathogen. Individual cows in a herd have been shown [9] to shed large variations of E. coli O157 numbers (0^10 5 g 31 ) and there is increasing concern [1] regarding environmental infection by E. coli O157, particularly in children associated with farm and countryside visits [2]. This risk is exacerbated because the minimum infectious dose is thought to be low ( 6 10 viable cells [10] and less than a few hundred [11]).…”