MINNESO
MINNESOTTA
DEP
AR
TMENT
DEPAR
ARTMENT
OF HEAL
TH
HEALTH
DISEASE CONTROL NEWSLETTER
August 1999
Volume 27, Number 4 (pages 33-36)
Detection and Investigation of Foodborne Illness
Outbreaks in Minnesota
In Minnesota, outbreaks of foodborne
illness are primarily investigated by
epidemiologists from the Minnesota
Department of Health (MDH) and
environmental health specialists from
local public health agencies or MDH. In
a few large cities and counties that
have their own epidemiologists, the
local agency may take primary responsibility for both epidemiologic and
environmental health investigations. In
these situations, the local health
department epidemiologists follow MDH
protocols, notify MDH of outbreaks
being investigated, and may seek
consultation and public health laboratory support for their outbreak investigations. These methods result in
Minnesota having a highly centralized
and standardized foodborne illness
surveillance system. This also allows
for rapid epidemiologic assessment of
outbreaks and the efficient use of public
health laboratory resources.
MDH identifies foodborne illness
outbreaks in two ways. The first is from
telephone calls from the public reporting suspected foodborne illness. The
second is through active laboratory
surveillance of selected bacterial and
protozoan pathogens.
Foodborne Illness Hotline
MDH has a statewide toll free hotline
(1-877-FOOD-ILL, i.e., 1-877-3663455) that allows the public to report
suspected foodborne illness. Individual
complaints to the hotline about a
restaurant or food item may precipitate
restaurant notification or an immediate
health inspection. All complaints are
recorded and maintained in an electronic format which allows epidemiologists to recognize multiple complaints
about a restaurant or food item. For
example, in the summer of 1998,
several calls to MDH led to the identification of two restaurant-associated
outbreaks which ultimately led to the
recognition of an international outbreak
of Shigella sonnei infections associated
with imported parsley.
In addition, a single report of illness
among two or more persons in different
households may prompt an outbreak
investigation. Many outbreaks have
been detected from a single complaint
reporting illness among a group of coworkers or friends who shared a
common meal.
It is often difficult to identify possible
causes of a person’s foodborne illness
because many people assume their
foodborne illness was caused by the
last meal they ate or the last meal they
ate away from home. This is not
usually the case.
Foodborne illness often has an incubation period of 24 hours to 4 days. Also,
because infection may occur at home or
at a restaurant it is difficult to identify
the source of an individual’s illness
without an epidemiologic investigation.
Laboratory Surveillance
MDH also detects outbreaks when
there is an increase in laboratory
submissions of notifiable foodborne
bacterial pathogens such as Salmonella, Shigella, E. coli O157:H7, or
Campylobacter, or when similar DNA
fingerprints among these pathogens
are identified. For example, MDH
identified the massive nationwide
Schwan’s ice cream Salmonella
outbreak in 1994 through this active
laboratory surveillance. Since that
time, numerous other outbreaks due to
restaurants or commercially available
food items have been detected in this
manner. Without stool cultures from
patients ordered by their health care
providers, these outbreaks would have
gone undetected. Furthermore, stool
cultures for bacteria and testing for
protozoan parasites such as
Cryptosporidium have the added
benefit of aiding in the detection of
waterborne outbreaks and outbreaks in
childcare settings, in which early
intervention can be critical.
Physician Involvement
MDH relies on physicians to order
appropriate stool tests on patients with
acute diarrheal illness to detect
foodborne pathogens. Although many
foodborne illnesses are viral and will
escape laboratory detection, opportunities are frequently missed to detect
bacterial infections and associated
outbreaks.
In 1996, MDH surveyed a random
sample of 1,000 physicians in primary
care and selected specialties to
determine provider practices with
respect to culturing patients who
continued...
present with acute diarrheal illness.
Acute diarrhea was defined as three or
more loose stools in a 24-hour period
with a duration of less than 7 days
before presentation. Four hundred
ninety-one (49%) Minnesota physicians
who had seen a patient with acute
diarrhea in the past 12 months were
included in the final analysis. Of these,
232 (48%) said they ordered a bacterial
stool culture on their last patient with
acute diarrheal illness. Respondents
said the most important influences on
their decision to order a culture were
duration, the presence of blood in the
stool, and fever.
Burden of Diarrheal Illness
in Minnesota
Beginning in 1996, a population-based
telephone survey to evaluate the
burden of diarrheal illness in Minnesota
was conducted through the Emerging
Infections Program (EIP). Between
March 1996 and June 1997, 2,448
Minnesota residents participated in the
survey. Of these, 257 (10%) reported
having diarrhea in the past 4 weeks; 16
(6%) of these visited a health care
provider. Only three respondents
(19%) with diarrheal illness and who
visited a health care provider said their
providers requested stool cultures.
Twenty-five respondents (10%) with
diarrhea reported that their diarrhea
lasted for at least 3 days. Among
those, five (20%) visited their physician;
only one (20%) of those five reported
that the physician requested a stool
culture.
Although these numbers are small, an
identical survey was conducted in four
other EIP sites, including Oregon and
selected counties in California, Connecticut, and Georgia. The combined
results from all five sites are similar to
Minnesota’s. In the five-site study,
1,674 (14%) of 11,732 respondents
reported having diarrhea in the past 4
weeks; of these, 131 (8%) visited a
health care provider. Thirty-three
respondents (25%) with diarrhea and
who visited a health care provider said
their provider requested a stool sample.
Among those who reported having
diarrhea in the past 4 weeks, 191
(11%) reported that their diarrhea
lasted at least 3 days. Among those,
40 (21%) visited their physician; 15
(38%) of those 40 said their physician
requested a stool culture.
Discussion
Extrapolating results of the population
survey to the entire population of
Minnesota, it is estimated that 6.6
million diarrheal illnesses occur among
Minnesota residents each year. Of
these patients, 515,000 seek medical
care, 342,000 are treated with antibiotics, 108,000 have a stool sample
requested, 48,900 visit an emergency
room, and 30,500 are hospitalized.
The 3:1 ratio of patients treated with
antibiotics versus those who had a
stool culture illustrates the frequency of
empiric treatment with antibiotics. This
practice is not recommended since
antibiotics are not indicated for the
treatment of many enteric bacterial
infections; rehydration and supportive
therapy remain the cornerstones of
treating gastrointestinal illness.
Furthermore, antimicrobial resistance in
bacterial enteric pathogens continues
to increase in Minnesota.
Foodborne Disease Outbreaks in Minnesota, 1981-1998:
The Importance of Norwalk-like Caliciviruses
From 1981-1998, 289 outbreaks of
foodborne illness occurred in Minnesota. Of these, 120 (42%) met epidemiologic criteria for being considered
outbreaks of Norwalk-like viral gastroenteritis (Table 1). These criteria
include a median incubation period of
24-48 hours, vomiting occurring with
greater frequency than fever, and a
median duration of illness of 24-48
hours. The constellation of symptoms
associated with Norwalk-like viral
gastroenteritis are often what the public
refers to as the “stomach flu” not
realizing that the infection may have
been transmitted to them via food
prepared by an infected person.
Laboratory confirmation of the presence of Norwalk-like caliciviruses was
obtained for two outbreaks in 1982, one
in 1993, three in 1996, three in 1997
and eight in 1998. During 1981-1998,
there were 54 outbreaks caused by the
major bacterial foodborne pathogens 32 (11%) due to Salmonella, eight (3%)
due to Campylobacter, eight (3%) due
to Escherichia coli O157:H7, and six
(2%) due to Shigella. Thus, the
number of foodborne illness outbreaks
caused by these bacterial pathogens
combined accounted for less than half
the number of outbreaks of viral
gastroenteritis.
A high proportion of the 120 foodborne
outbreaks of viral gastroenteritis were
continued on page 36
Table 1. Foodborne Illness Outbreaks in Minnesota,
by Agent, 1981-1998
Number (%) of Outbreaks
1981-1989
Agent
Norwalk-like virus
35 (33)
Clostridium perfringens 15 (14)
Salmonella
12 (11)
Staphylococcus aureus
7 ( 7)
Chemical
9 ( 8)
Bacillus cereus
7 ( 7)
Campylobacter
4 ( 4)
E. coli O157:H7
1 ( 1)
Other E. coli*
1 ( 1)
Hepatitis A virus
1 ( 1)
Shigella
2 ( 2)
Other**
2 ( 2)
Unknown
11 (10)
Total
107 (100)
1990-1998
85 (47)
21 (12)
20 (11)
5 ( 3)
3 ( 2)
3 ( 2)
4 ( 2)
7 ( 4)
5 ( 3)
5 ( 3)
4 ( 2)
6 ( 3)
14 ( 8)
182 (100)
Total
120 (42)
36 (12)
32 (11)
12 ( 4)
12 ( 4)
10 ( 3)
8 ( 3)
8 ( 3)
6 ( 2)
6 ( 2)
6 ( 2)
8 ( 3)
25 ( 9)
289 (100)
*Includes four enterotoxigenic E. coli, one enteropathogenic E. coli, and one other diarrheagenic E. coli.
**Includes three scombroid toxin, two ciguatera toxin, two Giardia, and one Cryptosporidium.
34
MDH Brochure on Foodborne Illness Available
Below are the text panels of a new
brochure on foodborne illness
available from MDH. Targeted for the
general population, this brochure is
designed to give an overview of
foodborne illness, as well as to
promote the MDH toll-free number to
report foodborne illness. Health care
providers may obtain, free copies of the
brochure by calling the MDH Acute
Disease Epidemiology Section at (612)
676-5414. Health care providers also
For a more
legible
copy
of this
brochure
via Adobe
Acrobat
Reader,
click here
35
are encouraged to call the toll-free
number to report possible foodborne
illness; testing for Norwalk-like
caliciviruses at MDH may be arranged
in some instances if appropriate.
associated with consumption of cold
food items that had been handled by ill
food workers. In 53 outbreaks (44%), ill
persons who handled the implicated
food items were identified. In 21
outbreaks (18%), food workers denied
illness but reported illnesses among
members of their household, suggesting either the possibility of transmission
from persons with asymptomatic
infections or their failure to adequately
wash hands and remove virus particles
acquired at home. In total, at least 74
(62%) outbreaks were likely the result
of contamination of foods by bare hand
contact. The occurrence of employee
illnesses and potential for ongoing
transmission of illness to patrons led to
the temporary closure of 11 restaurants.
Jan K. Malcolm
Commissioner of Health
Division of Disease Prevention and Control
Martin LaVenture, M.P.H. .......................... Acting Division Director
Kirk Smith, D.V.M., Ph.D. ....................................................... Editor
Sheril Arndt ......................................................... Production Editor
Richard N. Danila, Ph.D., M.P.H. ........ Acting State Epidemiologist
These results of statewide foodborne
disease surveillance in Minnesota
demonstrate that Norwalk-like
caliciviruses are the leading cause of
foodborne illness outbreaks, accounting
for 42% of all confirmed foodborne
disease outbreaks that occurred from
1981-1998.
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The Disease Control Newsletter is available on the MDH Acute Disease Epidemiology Section
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