Enhanced Detection of Sporadic Escherichia coli O157:H7 Infections -- New Jersey, July 1994
Infection with Escherichia coli O157:H7 causes an estimated
20,000 cases of diarrhea in the United States each year. Although
E. coli O157:H7 can be isolated using commercially available media,
many clinical laboratories do not routinely test stool samples for
the organism. In 1993, the Council of State and Territorial
Epidemiologists recommended that clinical laboratories begin
culturing all bloody stools -- and optimally all diarrheal stools
--
for E. coli O157:H7 (1). This report describes the investigation of
a pseudo-outbreak of E. coli O157:H7 infection that occurred in New
Jersey during July 1994 after a year-long increase in the number of
laboratories culturing all diarrheal specimens for this pathogen.
From June 1 through July 27, 1994, a total of 46
culture-confirmed cases of E. coli O157:H7 infection were reported
to the New Jersey Department of Health (NJDOH). In comparison, five
cases had been reported during the same period in 1993. To identify
the source of these infections, NJDOH and CDC conducted a
case-control study involving 23 cases and 46 age-matched controls.
A case was defined as a stool culture positive for E. coli O157:H7
in a New Jersey resident with onset of diarrhea during July 1994.
Of 22 case-patients for whom data were available, 18 (81%) reported
they had eaten a hamburger during the week before illness, compared
with 21 (47%) of 45 matched controls for whom data were available
(matched odds ratio=undefined, p less than 0.001). Of the
hamburgers eaten by case-patients, 73% had been prepared at home or
at picnics. No other food item or activity was associated with
illness.
An extensive traceback investigation was conducted to identify
the source of ground beef eaten by ill persons. The investigation
identified multiple retail and wholesale sources, suggesting these
cases were sporadic and not related to a common-source outbreak.
This finding was verified by laboratory tests that identified 17
different strains of E. coli O157:H7 among the 23 clinical
isolates. To assess the role of enhanced laboratory surveillance in
generating the increase in case reports, NJDOH surveyed 20 clinical
laboratories that had reported at least one E. coli O157:H7 isolate
during 1994. The number of laboratories culturing all diarrheal
specimens for E. coli O157:H7 had increased from two (10%) in July
1993 to 18 (90%) in July 1994.
Reported by: L Finelli, DrPh, E Crayne, E Dalley, MA, K Pilot, KC
Spitalny, MD, State Epidemiologist, New Jersey Dept of Health. Food
Safety Inspection Svc, US Dept of Agriculture. Foodborne and
Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases,
National Center for Infectious Diseases, CDC.
Editorial Note
Editorial Note: Since 1993, several outbreaks of E. coli O157:H7
infection have been detected as a result of increased laboratory
testing for this organism (2,3). The findings in New Jersey
demonstrate that increased testing can also substantially enhance
detection and reporting of sporadic infections. In January 1995, an
estimated 29% of clinical laboratories in the United States were
culturing all diarrheal specimens for E. coli O157:H7; however, the
proportion was increasing rapidly (CDC, unpublished data, 1995).
Therefore, public health officials should anticipate continuing
increases in reports of both sporadic and outbreak-related cases
and should evaluate the role of enhanced detection when an outbreak
is suspected.
A primary strategy for preventing infection with E. coli
O157:H7 is reducing risk behaviors through consumer education. In
New Jersey, the sudden increase in E. coli O157:H7 case reports was
reported widely by the news media. The press coverage provided
public health officials with an opportunity to inform the public
about the risks of eating undercooked ground beef, the need for
safe food-handling practices, and the potential for
person-to-person transmission.
Although traceback investigations can be important in
preventing E. coli O157:H7 infections, they should be undertaken
selectively. Traceback investigations are most useful when the
implicated vehicle is novel (e.g., salami) (3) or has a long shelf
life (e.g., frozen hamburger patties) (4). Because fresh ground
beef has a short shelf life and usually is derived from many
sources, traceback investigations involving this food item are
often unproductive.
An effective public health response to E. coli O157:H7
requires a timely and sensitive national surveillance system.
Through March 1995, a total of 33 states had enacted legislation
designating E. coli O157:H7 infection as a reportable disease (W.
Keene, State Health Division, Oregon Department of Human Resources,
personal communication, 1995). In addition, CDC has developed a
software module that enables states to report laboratory-confirmed
cases to CDC through the Public Health Laboratory Information
System (PHLIS). During January 1994-March 1995, a total of 38
states reported to PHLIS 1187 isolates of E. coli that were
positive for both the O157 and H7 antigens. Although PHLIS is a
passive, laboratory-based system, reported incidence rates in some
states have exceeded three cases per 100,000 population. With
expanded culturing by clinical laboratories and strengthened
reporting by states, these rates probably will increase.
References
Council of State and Territorial Epidemiologists. CSTE position
statement #4: national surveillance of Escherichia coli O157:H7.
Atlanta: Council of State and Territorial Epidemologists, June
1993.
CDC. Escherichia coli O157:H7 outbreak linked to commercially
distributed dry-cured salami -- Washington and California, 1994.
MMWR
1995;44:157-60.
Bell BP, Goldoft M, Griffin PM, et al. A multistate outbreak of
Escherichia coli O157:H7-associated bloody diarrhea and hemolytic
uremic syndrome from hamburgers: the Washington experience. JAMA
1994;272:1349-53.
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