Published Date: 1998-02-05 23:50:00
Subject: PRO/AH> E. coli, VTEC, Prevalence among farmers - Canada
Archive Number: 19980205.0224

E. COLI, VEROTOXIGENIC, PREVALENCE AMONG FARMERS - CANADA
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See Also

E. coli, beef, risk factors for contamination 980203220505
E. Coli 0157, host susceptibility 970130123255
E. Coli 0157, host susceptibility (02) 970203165342,
970204044620
Date: Wed, 04 Feb 1998 12:19:34 -0800
From: Dr. James Chin, CDPC-mail
Source: Canada Communicable Disease report - Vol. 24, No. 3, February 1, 1998

VEROCYTOTOXIGENIC ESCHERICHIA COLI INFECTION IN DAIRY FARM FAMILIES
Infection with verocytotoxigenic _E. coli_ (VTEC) continues to be an
important cause of enteric illness in Canada with 5.0 cases reported per
100,000 population in 1995, the most recent year for which complete data
are available. Infection results in a spectrum of illness including watery
diarrhea, bloody diarrhea, and the hemolytic uremic syndrome. Cattle are
believed to be the principal reservoir for this organism and consumption of
improperly cooked ground beef contaminated with bovine feces at slaughter
is an important risk factor for human infection. The VTEC serotype most
commonly isolated from clinical specimens in Canada is _E. coli_ O157:H7.
However, in both ground beef and bovine feces, _E. coli_ 0157:H7 is far
exceeded by non-O157 VTEC serotypes, several of which have been associated
with human illness.
Because dairy farm families are exposed to high levels of bovine VTEC
through direct contact with cattle manure and through consumption of
unpasteurized milk, they constitute a model of naturally occurring
transmission of these organisms from cattle to people. We report here on a
recently published Canadian study of dairy farm families undertaken to
investigate the role of VTEC serotypes of bovine origin in human disease…
Significant behavioral risk factors for infection were not identified, and
neither stool cultures nor serologic status were associated with clinical
illness. VTEC were isolated from stools cultures of 679 (46%) of cattle on
all 80 (100%) farms. Twelve cattle (0.8%) on seven (8.8%) farms were
positive for _E. coli_ O157:H7 on at least one visit.
A substantial number of dairy farm residents participating in this study
thus had evidence of current or past infection with VTEC on the basis of
stool cultures (6.3%) or serologic status (41.3%). VTEC infection occurred
at a very young age in subjects in this study, as indicated by both the
presence of VTEC in feces and seroprevalence of antibodies to VT1. Most of
these infections appeared to be due to VTEC other than serogroup O157 since
a much higher proportion of persons had antibodies to VT1 (41.3%) than to
O157 LPS (12.5%). Furthermore, _E. coli_ O157:H7 was isolated on only 8.8%
of farms and only one of the nine human VTEC isolates was E. coli O157:H7.
Seven of the eight other human VTEC isolates belonged to serotypes
previously associated with human infection. Our results thus provide
further evidence that non-O157 VTEC of bovine origin can infect humans…
The lack of disease due to VT1-producing _E. coli_ in farm residents in
this study may reflect protection associated with antibodies induced by
previous exposure. Exposure to the dairy-farm environment may have greater
health significance for urban residents and specific subgroups within the
rural community. Urban residents who visit farms, have direct contact with
cattle, or consume unpasteurized milk may be expected to have a higher risk
of VTEC infection and disease due to less prior exposure to VTEC. In
addition, children with declining maternal immunity, the elderly, and other
immunocompromised individuals who live on dairy farms may have increased
risk of infection and VTEC-associated disease.
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