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How to Treat
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Signs and
symptoms of
foodborne
illness
Treatment
Prevention
Emergence of
foodborne
disease
pathogens
Bioterrorism
readiness
The author
DR CRAIG DALTON
is public health physician,
Hunter New England Health
Service, and conjoint senior
lecturer, school of medical
practice and population
health, University of Newcastle.
Foodborne illness
Background
FOODBORNE illness can be caused
by a wide variety of micro-organisms,
biological toxins and chemical toxins.
While the primary manifestations
of foodborne disease are gastroenteric,
there are important neurological and
systemic presentations of foodborne
disease of which to be aware.
GPs are on the frontline of diagnos-
ing and treating foodborne disease,
and play an important role, individually and collectively, in preventing sporadic disease and controlling outbreaks.
Astute GPs have been instrumental
in identifying foodborne outbreaks
and alerting authorities to the problem. This allows public health inter-
ventions to control the outbreak,
thereby preventing illness and fatalities.
In Australia an estimated 4-7 million cases of foodborne illness occur
each year (11,000-19,000 cases a day).
Despite the increasing recognition of
foodborne disease as a problem, and
industry and government interventions
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to prevent it, the incidence may be
increasing.
What is foodborne illness?
Foodborne illness may be defined as
any illness in two or more people
related to the consumption of food
and is not limited to gastroenteritis.
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How to treat – foodborne illness
from previous page
While GPs predominantly see
sporadic or isolated single
cases of foodborne illness, the
single case may be part of a
larger outbreak.
One of the challenges to the
GP is differentiating foodborne illness from other routes
of transmission such as
person-to-person, waterborne
or zoonotic. Without a history
of similar illness related to
food it is difficult to identify a
foodborne aetiology unless:
mission (eg, Bacillus cereus,
Staphylococcus aureus
[enteric disease], Listeria
monocytogenes).
As these agents are not
necessarily the most common
causes of foodborne disease
in Australia (table 1), which
typically present with gastroenteritis, GPs often rely on
epidemiological links established through the history
and on laboratory support to
confirm foodborne illness.
Working with public health
The signs and symptoms are
pathognomonic of specific
foodborne diseases that do
not have an alternative
route of transmission (eg
ciguatera poisoning from
warm-water finfish carrying
ciaguatera toxin, and scombroid poisoning caused by
formation of histamine
during improperly controlled temperature storage).
■ The laboratory confirms an
agent that is almost exclusively foodborne in trans■
Table 1: Causes and treatments of foodborne illnesses
Organism
Signs and symptoms
Illness duration
Associated foods
Bacillus cereus
(diarrhoeal toxin)
Abdominal cramps, watery
diarrhoea, nausea
24-48 hours
Meats, stews, gravies
Bacillus cereus
(preformed enterotoxin)
Sudden onset of severe nausea and
vomiting. Diarrhoea may be present
24 hours
Improperly refrigerated cooked
and fried rice, meats
Campylobacter jejuni
Diarrhoea (may be bloody), cramps,
fever, vomiting
2-10 days
Raw or under-cooked poultry,
unpasteurised milk, contaminated water.
Clostridium botulinum
— children and adults
(preformed toxin)
Vomiting, diarrhoea, blurred vision,
diplopia, dysphagia, descending
muscle weakness
Variable (days to months).
Can be complicated by
respiratory failure and death
Home-canned foods with a low acid content,
improperly canned commercial foods,
home-canned or fermented fish, herbinfused oils, baked potatoes in aluminum foil,
cheese sauce, bottled garlic, foods held
warm for extended periods of time
Clostridium perfringens toxin
Watery diarrhoea, nausea, abdominal
cramps; fever is rare
24-48 hours
Meats, poultry, gravy, dried or pre-cooked
foods, poor-quality storage, poor temperature
control after cooking
Enterohemorrhagic E coli
(EHEC), including E coli 0157:
H7,0111 and other Shiga-toxinproducing E coli (STEC)
Severe diarrhoea that is often bloody,
abdominal pain and vomiting.
Usually little or no fever. More
common in children aged <4 years
5-10 days
Apart from the notable SA Metturst outbreak,
most cases in Australia are sporadic.
Overseas: undercooked beef, especially
hamburgers, unpasteurised milk and juice, raw
fruits and vegetables (eg, sprouts), salami (rarely),
and contaminated water
Enterotoxigenic E coli (ETEC)
Watery diarrhoea, abdominal
cramps, some vomiting
3 to >7 days
Water or food contaminated with
human faeces
Listeria monocytogenes
Fever, muscle aches, nausea or
diarrhoea. Pregnant women may have
mild flu-like illness, and infection can
lead to premature delivery or stillbirth.
Elderly or immunocompromised patients
may have bacteraemia or meningitis.
Infants infected from their mothers are
at risk for sepsis or meningitis
Variable
Fresh soft cheeses, unpasteurised or
inadequately pasteurised milk, ready-to-eat
deli meats, hot dogs
Salmonella spp
Diarrhoea, fever, abdominal cramps,
vomiting. S typhi and S paratyphi
produce typhoid with insidious onset
characterised by fever, headache,
constipation, malaise, chills, and
myalgia; diarrhoea is uncommon,
vomiting is usually not severe
4-7 days
Contaminated eggs, poultry, unpasteurised
milk or juice, cheese, contaminated raw fruits
and vegetables (alfalfa sprouts, melons).
S typhi epidemics are often related to faecal
contamination of water supplies or
street-vended foods
Shigella spp
Abdominal cramps, fever, and
diarrhoea. Stools may contain
blood and mucus
4-7 days
Food or water contaminated with human
faecal material. Usually person-to-person
spread, faecal-oral transmission. Ready-to-eat
foods touched by infected food workers, eg,
raw vegetables, salads, sandwiches
Staphylococcus aureus
(preformed enterotoxin)
Sudden onset of severe nausea and
vomiting. Abdominal cramps.
Diarrhoea and fever may be present
24-48 hours
Unrefrigerated or improperly refrigerated
meats, potato and egg salads, cream pastries
Yersinia enterocolytica and
Y pseudotuberculosis
Appendicitis-like symptoms
(diarrhoea and vomiting, fever, and
abdominal pain) occur primarily in
older children and young adults.
There may be a scarlatiniform rash
with Y pseudotuberculosis
1-3 weeks, usually
self-limiting
Under-cooked pork, unpasteurised milk,
tofu, contaminated water
Hepatitis A
Diarrhoea, dark urine, jaundice and
flu-like symptoms, ie, fever, headache,
nausea and abdominal pain
Variable: 2 weeks-3 months
Shellfish harvested from contaminated
waters, raw produce, contaminated
drinking water, uncooked foods and
cooked foods that are not reheated
after contact with an infected food handler
Noroviruses
(and other caliciviruses)
Nausea, vomiting, abdominal cramping,
diarrhoea, fever, myalgia and some
headache. Diarrhoea is more prevalent
in adults, vomiting is more prevalent
in children
2-60 hours
Shellfish, faecally contaminated foods,
ready-to-eat foods touched by infected
food workers (salads, sandwiches,
ice, cookies, fruit)
Rotavirus
Vomiting, watery diarrhoea, low-grade
fever. Temporary lactose intolerance may
occur. Infants, children, the elderly and
immunocompromised are especially
vulnerable
4-8 days
Faecally contaminated foods. Ready-to-eat
foods touched by infected food workers
(salads, fruits)
Bacteria and bacterial toxins
Viruses
40
| Australian Doctor | 15 April 2005
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authorities is essential for the
full assessment of epidemiological and laboratory information. The epidemiological
clue to look for is a common
shared meal among a group,
with similar onset times and
similar illness.
It is difficult to rule out a
non-foodborne aetiology
when GI illness occurs in families, because family members
obviously share common
foods and are at greater risk
of person-to-person transmission of GI pathogens.
If a group of ill persons
does not live together and has
shared a meal, with no other
contact in the days to weeks
before, or the days after, the
meal, a foodborne aetiology
becomes more likely.
It is important not to dismiss a foodborne aetiology
because the onset of illness
from the time of consumption
of the food (the incubation
period) is considered too
short or too long without first
examining the broad range of
incubation periods associated
with foodborne agents. As
can be seen in table 2, incubation periods range from
half an hour to several weeks.
Common foodborne agents
in Australia
Surveillance of foodborne disease is coming of age in Australia thanks to the initiation
of the OzFoodnet surveillance
network in collaboration with
local and state reference laboratories.
Estimates of incidence of
foodborne illness come from
two sources (both initiating
mainly from GPs) — laboratory surveillance of sporadic
disease, and reports of outbreaks involving two or more
cases.
The major causes of foodborne disease in Australia are
viruses, bacteria and bacterial toxins.
While foodborne outbreak
reports can include any agent
as long as the route of transmission is foodborne, laboratory-based surveillance reports
are generally restricted to
pathogens notifiable under the
state public health acts. These
are generally limited to salmonellosis, campylobacteriosis (except in NSW), shigellosis, Shiga-toxin producing E
coli infection, and hepatitis A.
The two major sources of
surveillance data for foodborne disease in Australia are
the National Notifiable Disease Surveillance System,
(NNDSS) and foodborne outbreak summaries compiled by
OzFoodnet.
The most common foodborne disease reported to the
NNDSS in recent years is
campylobacteriosis, with
about 15,000 cases (probably
about 20,000 if NSW reported
cases to NNDSS) followed by
salmonellosis, with about
7000 cases reported annually
in recent years. These notifications include foodborne
infection and transmission by
other routes.
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Table 2: Number of outbreaks caused by selected
foodborne disease agents, with typical
incubation periods
Agent
Bacterial
Salmonella spp
Clostridium
perfringens
Campylobacter
jejuni
Listeria
monocytogenes
Staphylococcus
Bacillus cereus
Number of
outbreaks,
1995-2000 (%)
131 (61%)
75 (35%)
30 (14%)
Typical incubation
periods
6 (3%)
2-5 days
5 (2%)
1-70 days
5 (2%)
2 (1%)
1-6 hours
1-6 hours for vomiting
toxin strain, 10-16 hours
diarrhoeal strain
1- 8 days
Shiga-toxinroducting E coli
Viral
Norovirus*
Hepatitis A
3 (1%)
Chemical
Ciguatera
34 (16%)
23 (11%)
Unknown
Total**
6 (3%)
2 (<1%)
1-3 days
8-16 hours
12-48 hours
15-50 days
28 days average
2-6 hours for
GI and neurological
symptoms, 2-5 days for
cardiovascular effects
40 (19%)
214
*This is certainly an underestimate of norovirus outbreaks — as many as
50% of foodborne outbreaks may be associated with norovirus infection
but many are missed because it is not detected with standard culture
methods.
**Outbreaks due to less common agents were excluded, so columns do
not add to total.
Norovirus — an emerging pathogen you need to
know
NOROVIRUS, previously known variably as Norwalk or
Norwalk-like virus, small round structured virus or calicivirus
(not the rabbit pathogen) is increasingly recognised as a major
cause of foodborne and person-to-person gastroenteritis.
This virus may be the most common single cause of
gastroenteritis in adults in Australia. It often causes epidemics
because:
■ It requires a very small dose to cause infection.
■ It has been shown to spread through the air.
■ It survives well on surfaces in the environment.
■ Immunity is short lived, allowing frequent reinfection.
The typical picture of norovirus is the rapid spread of an illness characterised by vomiting and diarrhoea. The time from
exposure to onset of illness (the incubation period) is usually
24-48 hours, with a 1-2-day duration of illness.
This virus is being increasingly diagnosed through the use of
PCR technology in reference laboratories because it is not
detected in standard stool cultures. Testing is not usually indicated except in an outbreak situation, and your local public
health department can help with testing.
Norovirus is responsible for many of the gastroenteritis outbreaks that occur in aged-care facilities, cruise ships and
schools. There may be low-level shedding of the virus in stool
for days and perhaps weeks after cessation of diarrhoea, and
food handlers are usually excluded from work for two days
after recovery, with instruction to maintain fastidious hand
hygiene.
There is evidence that a new strain, known as the Farmington Hills strain, has been circulating worldwide since about
2002 and is responsible for many epidemics.
Laboratory surveillance
data are limited by the many
barriers to detection and
reporting, beginning with
individual patients’ decisions
to present to their GP, the
decision to request a stool
specimen and patients’ compliance with these requests,
through to the laboratory
test selection and sensitivities.
These barriers are estimated to result in only one in
three to one in 38 cases of
salmonellosis in the community actually being detected
by surveillance systems and
appearing in surveillance
data. Similar underestimation
of campylobacteriosis cases
also occurs.
Summaries of outbreak
reports in Australia from
1980 to 2003 show that salmonellosis is the most
common cause of outbreaks
detected by state health
departments, followed by
Clostridium perfringens infection. More recently, norovirus
infection (see box) is increasingly detected as a result of
wider availability of PCR testing for viral nucleic acid (table
2).
Signs and symptoms of foodborne illness
THE major objectives in
assessing the patient are to
assess fluid loss and immediate hydration needs and to
develop a differential diagnosis of potential agents to
guide treatment and investigation.
History should include
asking about similar illness in
family or close friends, and
common meals shared with
other ill persons up to 10
days before onset of illness,
but especially in the three
days before illness.
Attendance at large catered
functions, especially those
catered by non-professional
workers, and travel may be
important clues. Consumption of high-risk foods such
as uncooked seafood or
undercooked meats and poultry is also important.
In exploring alternatives to
foodborne transmission,
drinking from raw water
sources such as creeks (or
swallowing water while
swimming), exposure to animals and/or their faeces
should be considered..
The history of foods consumed is not as predictive as
is commonly believed.
Chicken is often associated
with outbreaks of salmonellosis but many other foods
that may be contaminated
with salmonella must be considered.
In a review of outbreaks of
foodborne illness in Australia
from 1995 to 2000, only
13% of salmonella outbreaks
were attributed to chicken —
comparable to the number
attributed to eggs (11%) and
sandwiches (9%).
Foods previously considered low risk, such as salads
and fruits, have also been
implicated in salmonella outbreaks. Because norovirus
can be spread by contamination of food with vomit or
faeces from infected food
handlers or guests, almost
any food subject to handling
without further cooking may
spread this disease.
It is difficult to predict the
agent responsible for the outbreak from the history and
physical examination, apart
from a small number of
agents with pathognomonic
syndromes. However, it is
possible for the GP to narrow
the range of possibilities.
Individual patients may
have different presentations
depending on age and underlying immunity, dose ingested
and treatment. A patient may
experience a range of symptoms but there are clues to
aetiology based on the severity and the predominance of
specific symptoms:
■ Patients whose major complaint is vomiting are likely
to have a norovirus infection or a bacterial toxin
such as Staphylococcus
aureus or Bacillus cereus
toxins.
■ Patients with severe abdomwww.australiandoctor.com.au
Table 3: Guide to outbreak scenarios of common
foodborne disease agents
Foodborne
agent grouping
Characteristics
of presentation
Likely
agents
Viral
>50% of group vomiting
24-48 hour incubation
<3-day duration
Norovirus*
Bacterial toxin
<20-hour incubation
<24-hour duration
Clostridium
perfringens,
Bacillus cereus,
Staphylococcus
aureus
Bacterial enteritis 1-4-day incubation,
>3-day duration. Fever,
<50% of group
vomiting, cramps,
possibly bloody stools
Marine toxins
<6 hours’
incubation
<1 hour
incubation
Salmonella spp,
Campylobacter
jejuni,
Shigella spp
Parasthaesias and
temperature reversal
typical of ciguatera
Ciguatera toxin
Flushing, rash,
tingling/burning mouth
Scombrotoxin
*Norovirus was previously known as Norwalk and the Norwalk-like
viruses, small round structured viruses, and calicivirus.
inal cramping, fever, chills
and prostration are more
likely to have bacterial
enteritis.
■ Bloody diarrhoea is very
suggestive of invasive bacterial enteritis but should be
differentiated from haemorrhoids associated with prolonged diarrhoea.
■ Diarrhoea lasting less than
24 hours suggests a preformed toxin or a short
norovirus illness.
■ Diarrhoea lasting longer
than a week, with fewer
systemic manifestations, is
suggestive of parasitic disease.
■ Neurological manifestations
are suggestive of marine
toxins or botulism (table 3).
Additional clues to aetiology may be provided from
the histories of the wider
group affected in an outbreak
because this provides more
information on the prevalence of symptoms or incubation periods.
While this article focuses
on the more common agents
seen by GPs in Australia, a
more extensive description of
clinical presentations is available for downloading at the
American Medical Association web site (see Online
resources, page 43).
Examination is unlikely to
be helpful for identifying aetiology of gastroenteritis but is
important in assessing hydration and exploring any neurological manifestations.
When to request a stool
specimen
A stool specimen is critical to
identifying the agent and
provides several benefits to
the patient and to public
health.
The benefits to the patient
include the ability to provide
a prognosis in terms of duration of illness, the risk of
transmitting the disease to
family members and, in
workplaces, the precautions
required to control transmission and the potential for
treatment and its benefits.
From a public health perspective it may allow a link to
be made to a wider outbreak
to allow a recall of a contaminated food item and allow
appropriate exclusion of the
patient from sensitive occupations such as food handling or
patient care. GP reports to
health departments help build
a database of food safety
problems to help develop
better food safety programs.
However, stool cultures are
expensive and most gastroenteritis is self-limiting, so it
would be inappropriate to
test every case of diarrhoea.
The extent of testing is a
matter for clinical judgment,
but the presence of any of the
following signs and symptoms or characteristics may
be an indication for testing:
■ Bloody diarrhoea or severe
abdominal pain.
■ Significant weight loss.
■ Dehydration.
■ Fever >38.5˚C.
■ More than three days of
diarrhoea.
■ Suspected outbreak.
■ Hospitalisation or deaths
among similarly affected
cases.
■ Infant, elderly or immunocompromised patient.
A standard request to a
laboratory for microscopy,
culture and sensitivity on a
stool specimen will usually
only be plated on media that
will allow easy identification
of salmonella spp, Campylobacter jejuni and shigella
spp. Less common bacterial
pathogens such as vibrio and
yersinia spp may not be identified on standard plates at
your local laboratory unless
specific requests are made.
Likewise PCR for viruses
and toxin tests will not be
performed routinely. Public
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How to treat – foodborne illness
Typically only
about 20% of
patients who are
requested to
provide a
specimen actually
provide one.
from page 41
health authorities will request
these tests or forward the
specimens to a reference laboratory if these more specialised tests are required.
Illnesses with long incubation periods or diarrhoea lasting longer than seven days
may be due to parasitic infection, so a request for ova and
parasite examination may be
appropriate.
Collecting stool specimens
is often a challenge for
patients. Typically only about
20% of patients who are
requested to provide a specimen actually provide one.
Patients may be assisted in
the collection with simple
guidelines such as placing
paper across the toilet bowl
or placing a plastic container
in the toilet. Written guidelines are available from many
health departments.
Surprisingly, even patients
seriously ill with diarrhoea
can be hospitalised and discharged without having a
stool specimen collected
while in hospital.
In situations when it is
imperative to get a specimen
early, for example, a large
outbreak of a serious or fatal
illness, collecting a rectal
swab using a standard cotton
swab, placed in bacterial
transport media, should be
considered opportunistically.
Swabs will likely only be of
use when bacterial enteritis is
suspected, as they do not provide sufficient stool for viral
or parasitic investigations.
Differential diagnoses for
gastroenteric presentations
include inflammatory bowel
disease, irritable bowel syndrome, adverse reactions to
medications and structural
and functional intestinal aetiologies.
If a specific agent identified
in an individual patient, table
4 provides an estimate of the
probability that the illness
was due to foodborne transmission.
Table 4: Probability of the presence of a specific
agent in an individual patient being due to
foodborne transmission
Agent
Percentage foodborne
transmission
Staphylococcal food poisoning
100%
Clostridium perfringens
100%
Scombrotoxin
100%
Ciguatera toxin
100%
Listeria monocytogenes
99%
Salmonella, non-typhoidal
95%
Campylobacter jejuni
80%
Norovirus
40%
Shigella spp
20%
Giardia lamblia
10%
Hepatitis A virus
5%
Adapted from Mead, 1999.
Treatment
ILLNESS due to the most
common causes of foodborne disease in Australia
(norovirus, Salmonella spp,
and Clostridium perfringens)
is usually self-limited and
does not require more than
oral fluid replacement and
supportive care. IV therapy
may be required for severe
dehydration.
Antibiotic therapy has no
positive clinical effect on the
treatment of Salmonella
diarrhoea in healthy children
and adults with non-severe
diarrhoea and may prolong
excretion of Salmonella
(level 1A evidence).
Severe extra-intestinal
manifestations of salmonellosis include septicaemia,
meningitis, pneumonia,
endocarditis, pericarditis,
and hepatic or splenic
abscess. Recommended
antibiotic regimens for treating such invasive disease are:
■ Ciprofloxacin
(child:
10mg/kg up to) 500mg
orally, 12-hourly for 5-7
days, or:
■ Azithromycin
(child:
20mg/kg up to) 1g orally
on the first day, followed
by (child: 10mg/kg up to)
500mg daily for a further
six days (total treatment
duration seven days).2
While randomised controlled trials have found that
ciprofloxacin reduces the
duration of communityacquired diarrhoea by 1-2
days
compared
with
placebo, the relative high
incidence of viral disease in
Australia and the self-limiting nature of most GI illnesses do not support the
use of empirical treatment
for uncomplicated illness
acquired in Australia. A
Cochrane review published
in 1999 supports this recommendation.
Although diphenoxylate
and loperamide have both
been shown to be effective
in controlling diarrhoea in
randomised controlled trials,
they should be avoided in
children and the elderly
because of potential adverse
reactions.
Early studies suggested
patients with severe febrile
bacterial enteritis were more
likely to have a prolonged
illness if treated with
antidiarrhoeal agents, except
if they received concomitant
antibiotic therapy. If a
patient with fever or severe
abdominal pain requires
antidiarrhoeal medication —
to allow travel, for example
— consideration should be
given to concomitant administration of a fluoroquinolone.
Exclusions for ill patients
Patients with current or
recent diarrhoea may be an
infection risk to others, particularly in sensitive occupations such as food handling,
health care and childcare.
While guidelines for exclusion from work vary across
jurisdictions depending on
the pathogen, in general,
patients working in these
sensitive areas should be
excluded from work until
the diarrhoea has resolved,
and they should practise fastidious hand-washing practices after toileting.
A negative stool culture is
not required for return to
work after salmonellosis;
however, testing may be
required in some settings
after diagnosis of infections
with a higher propensity for
person-to-person transmission, such as shigella, shigatoxin-producing E coli infection or typhoid.
Patients with hepatitis A
will generally be excluded
from sensitive occupations
for seven days from the
onset of jaundice.
Contact your local public
health department for guidance on duration of exclusion and retesting for specific pathogens.
Reporting of foodborne
outbreaks
Notification of foodborne
outbreaks (the same illness
in two or more persons,
related to the consumption
of food) by doctors is
mandatory under public
health acts across Australian
state and territory jurisdictions.
Doctors should report any
incident affecting two or
more persons if they have
any suspicion of foodborne
illness. It is also appropriate
to report single cases occurring at sporadic intervals if
they have a link to a
common food outlet.
Epidemiologists will interview patients, looking for
common food exposures. If
a point source of the outbreak is identified, a cohort
study may be initiated to
explore food-specific attack
rates to look for a foodborne
link — essentially an elevated relative risk associated
with a single food.
If a foodborne link with a
commercial establishment is
established or suspected,
food inspectors will inspect
the food facility for
breaches of food standards,
including temperature controls, cross-contamination
and hand washing. They
may collect food specimens
or environmental swabs for
culture.
Epidemiologists may conduct case finding by calling
other parties booked at the
facility on the same day or
subsequent days to look for
further cases.
Prevention
Higher-risk foods
THE main purpose of defining
higher-risk foods to a GP audience
is to help identify foods that may
be responsible for outbreaks and
to help doctors counsel potentially
vulnerable patients about the risks
of foods they may wish to avoid.
Equally, vulnerable patients should
be counselled about risky foodhandling practices.
Examples of higher-risk foods
identified by Food Standards Australia include:
■ Cold processed meats.
■ Cold cooked chicken.
■ Paté.
■ Salads prepared in advance for
salad bars, and packaged salads.
■ Chilled seafood, for example, raw
oysters, sashimi, sushi; smoked
seafood; ready-to-eat peeled
prawns.
■ Soft cheeses.
■ Soft-serve ice-cream.
■ Unpasteurised dairy products, for
example, raw goats’ milk.
42
| Australian Doctor | 15 April 2005
Salad bars where
prolonged storage
or high temperatures allow bacterial growth.
■ Delicatessen
foods displayed
such that crosscontamination can
occur.
The Food Standards
Australia guidelines apply
equally well to preventing
infection with other bacterial foodborne pathogens.
Patients should be counselled to adopt good food
hygiene practice by keeping
hot foods hot (>60˚C) and
cold foods cold (<5˚C ) and
avoiding cross-contamination
between raw meats and ready-toeat foods.
The approach to counselling
patients on these higher-risk foods
and food practices must be balanced against their quality of life.
■
While there is no
doubt that many of
the foods listed pose
an elevated relative
risk of food poisoning,
the
absolute risk per
serving is still
extremely small.
It may be more
appropriate to counsel
some patients to avoid
higher-risk foods only
during the short selected
periods when they are
under maximum immune
suppression from their illness or therapy.
Higher-risk patients
There are about 70 cases of listeriosis annually in Australia, of
which 30-50% are fatal. Food
Standards Australia provides a
patient-information brochure (see
under Online resources) that
identifies the following patients
www.australiandoctor.com.au
as being at higher risk of listeriosis:
■ Pregnant women, their unborn
and newborn children.
■ Older people (generally considered to be those over 65-70).
■ People of all ages whose immune
systems have been weakened by
disease or illness, for example,
cancer, leukaemia, AIDS, diabetes, liver or kidney disease
■ Anyone taking medication that
can suppress the immune system,
for example, prednisone or cortisone, including organ transplant
patients.
While L monocytogenes is the
foodborne pathogen that most
selectively impacts the immunocompromised and elderly, other
pathogens may also affect vulnerable patients.
Higher-risk settings
In a summary of 214 outbreaks of
foodborne disease in Australia
from 1995 to 2000:
Restaurants and commercial
caterers were associated with the
highest number of outbreak
reports and cases.
■ Outbreaks in hospitals and agedcare facilities were responsible for
35% of the 20 deaths.
■ The most frequently implicated
food vehicles in the 173 outbreaks with known vehicles were
meats, 64 cases (30%), fish 34
(16%), seafood 13 (6%), salad
12 (6%), sandwiches 11 (5%)
and eggs 9 (4%).
■ Chicken, the most frequently
implicated meat, was associated
with 27 outbreaks (13%).
The Ministerial Policy Guidelines
on Food Safety Management in
Australia prioritised raw oysters
and other bivalves, processed meats
(particularly uncooked fermented
meats), food service facilities for
high-risk patients, and catering
operations serving food to the general public for food safety programs.
■
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Emergence of foodborne disease pathogens
SEVERAL factors may contribute to an increasing incidence of food-borne disease,
including changes in diet,
global distribution of foods,
expansion of commercial food
services and new methods of
large-scale food production.
Australian diets have diversified rapidly in the past 30
years, so much so that the
recent outbreak of Salmonella
enterica serotype Montevideo
in NSW associated with tahini
imported from Egypt was not
restricted to any particular
ethnic group.
Fat and salt that inhibit bacterial growth are being
reduced in many food lines
and there is greater consumption of raw and pre-prepared
salads. Bacteria can grow on
cut vegetable and fruit surfaces, so the time from cutting/processing to consumption presents a potential
hazard. It is important to recognize that contamination of
fruit and vegetables can occur
anywhere from paddock to
plate.
Salad sprouts are an example of a food that is increasingly consumed by humans.
In the past they were almost
exclusively grown as animal
fodder and hence they are
often grown in close proximity to livestock, allowing contamination from manure in
run-off from paddocks.
Increasing urban and
human impact on oystergrowing estuaries makes it difficult to protect oysters from
faecal contamination. Largescale livestock production has
become an industrial enterprise with a movement away
from free-ranging animals to
intensive livestock facilities.
These new agricultural environments provide new ecological niches for the emergence, entrenchment, and
dissemination of new
pathogens. Concerning examples from overseas include the
transovarian transmission of
Salmonella enteritidis phage
type 4 to the inside of chicken
eggs in the USA and Europe.
The use of antibiotics as a
growth promoter in livestock
(by changing the bacterial pro-
Medicolegal considerations
Assigning blame
It is important to remember that it is almost impossible to determine that food is the cause of a
single case of gastroenteritis. No matter how severe the vomiting or diarrhoea experienced after a
suspect meal, it is impossible to attribute it to a specific meal on the basis of history.
Anyone who vomits during waking hours has usually eaten within the previous few hours, so the
most recent meal (no matter what the patient’s perception of it on being re-presented with it partially digested) should not be under particular suspicion, given that foodborne illness incubation
periods range from less than an hour to many weeks, depending on the agent.
Neither should blame be assigned only to take-away or restaurant meals. GPs should elicit their
patients’ concerns about high-risk or suspect foods that the patient is concerned about, but not
pass judgment on the likely source.
It is best left to health and food safety agencies to explore the links and identify the cause under the
protection of their respective acts. GPs may be drawn into public accusations promoted in the
media or further legal action if they assign blame to a particular food or retail food outlet.
Implications of not reporting outbreaks
GPs have a legal obligation to report foodborne disease outbreaks in all jurisdictions across Australia. While there is little chance of a doctor being fined by a health department for not reporting a
foodborne outbreak, the greater liability is that failure to comply with the public health act may
result in delayed recognition of an outbreak by the health department, resulting in more illness or
deaths.
In the coronial inquest into the death of a four-year-old girl in the South Australian mettwurstrelated outbreak of 1995, the coroner closely reviewed the actions of each doctor to determine if
failure to communicate clinical findings contributed to delayed recognition of the outbreak.
Time can be of the essence in identifying and recalling a food or closing a restaurant. In the mettwurst outbreak, after weeks of investigation the mettwurst was recalled on a Monday but the child
who died ate it on the Saturday two days before.
It is important to remember that, while many of the patients you will see will have mild self-limited
illness, there may be others at the extremes of age or who are immunocompromised who may die
from the same infection.
Prior judgments have established that GPs owe a duty of care to people other than their own
patients. The trigger to reporting is a history of two or more people with illness who have shared a
common meal. This report transfers responsibility to the health department to explore the link.
Exclusion of ill persons from sensitive occupations and facilities
People with gastroenteritis may need to be excluded from work as food handlers, healthcare workers, childcare or aged-care workers.
Children and long-term-care patients may need to be excluded from daycare and long-term-care
facilities until their illness has resolved and for a buffer period thereafter, depending on the
pathogen.
Seek advice from the local health department on a case-by-case basis. It is important to remember
that some pathogens may continue to be excreted by asymptomatic patients.
file in the gut, less food is
required for weight gain) has
led to infections in human
with resistant and multiresistant pathogens.
Shiga-toxin-producing E
coli first came to notice as a
cause of haemolytic uraemic
syndrome in the US in the
1980s. The first outbreak of
this syndrome in Australia
was associated with consumption of mettwurst (a
fermented but uncooked
processed meat) in SA in
1995.
It may be that diets high
in grain, associated with
feed-lots, promote the
growth of this type of E coli,
which
has
somehow
acquired the genes to produce Shiga toxin. The toxin
is cytotoxic to microvasculature and causes renal failure, strokes and anaemia.
Safe food handling knowledge required in today’s
domestic kitchen now
greatly exceeds the simple
infection-prevention steps
relied on when grilling lamb
chops and boiling three vegetables.
It may require programs in
early high school years and
tight linking to the marketing
of food to improve food handling. The increasing capacity
of Australian governments to
implement food safety standards through better policy,
Author’s case study
Table 5: Leading foodborne bioterror agents and
selected characteristics
Agent
Clinical
syndrome
Case
fatality
Other
characteristics of
microbe or illness
Botulinum
toxin
Descending
paralysis,
respiratory
compromise
5%
treated
95% of patients
need hospitalisation;
60% of patients
need intubation
Salmonella
serotypes
(excluding
S typhi)
Acute
diarrhoeal
illness, 1-3%
chronic
sequelae
>1%
Hardy organism,
lengthened survival
in the environment
Salmonella
typhi
Acute febrile
illness,
protracted
recovery,
10% relapse,
1% intestinal
rupture
10%
untreated,
1%
treated
Clinical syndrome
unfamiliar in
developed countries;
long incubation
period;
asymptomatic
carrier rate of 3%
Shigella
spp
Acute
diarrhoea,
often bloody
<1%
(most
common
species in
developing
countries)
Shigella
Dysentery,
dysenteriae seizures
type 1
Up to 20%
(treated)
Causes severe
dysentery, toxic
megacolon,
haemolytic uraemic
syndrome,
convulsions in
children
Shigatoxinproducing
E coli
Acute
1%
bloody
diarrhoea,
5%
haemolytic
uraemic
syndrome,
renal
complications
Long-term sequelae:
hypertension, stroke,
renal insufficiency/
failure, neurological
complications
Vibrio
cholerae
Acute, lifethreatening
dehydrating
diarrhoea
Historically causes
massive waterborne
epidemics in areas
with poor sanitation
Up to 50%
untreated,
1%
treated
Adapted from Sobel J, et al, 2002.
standards and state food
authorities will help improve
commercial food safety.
Bioterrorism readiness
GPs are on the front line of
naturally occurring outbreaks,
so they will be integral to Australia’s preparedness and
response to potential bioterror threats, which are, admittedly, extremely low.
Familiarity with the clinical syndromes associated
with the leading foodborne
bioterror agents, as prioritised by the CDC (table 5),
will enhance preparedness.
References available on request
Online resources
Preventing a foodborne disease
outbreak
A GP sees a 40-year-old woman who has
had vomiting and diarrhoea for four days.
She describes fevers and chills and severe
abdominal pain for two days.
The GP asks if she has been in contact
with anyone with similar illness recently.
The patient advises that her best friend
had onset of similar symptoms the same
day. They had had lunch at a local café
two days before the illness but otherwise
had not seen each other during the previous 10 days.
The GP reports this illness because a
possible foodborne outbreak to the local
public health department, which sup-
ported the GP’s decision to perform a
routine stool culture because bacterial
enteritis was the provisional diagnosis.
The public health department asks the
patient for her friend’s phone number
and arranges for an officer to drop off a
stool-collection kit at the friend’s home.
The specimen was picked up that afternoon.
The GP reviews the morning’s pathology results and finds a stool culture positive for salmonella in another 29-yearold woman he had seen five days ago
with similar symptoms. He contacts the
woman to give her the result and finds
she has also eaten at the same café.
This information is phoned in to the
public health department, which then
requests copies of the restaurant’s
bookings on the day of the implicated
meals and calls patrons to see if anyone
else has been sick. Many are ill and are
subsequently found to have the same
type of salmonella infection.
Food inspectors find squeezable sauce
bottles containing a range of dressings
containing perishable ingredients such
as eggs, which were stored unrefrigerated in the café. Cultures from the
sauce revealed the same subtype of salmonella that infected the patients. The
café removes all sauces, educates all
staff on food hygiene and the outbreak
is brought under control.
www.australiandoctor.com.au
National Notifiable Diseases Surveillance System This
application generates summary data for notifications of
communicable diseases reported to Australia’s National
Notifiable Diseases Surveillance System (NNDSS). All
notifiable foodborne diseases are available here:
www1.health.gov.au/cda/Source/CDA-index.cfm
Food Standard Australia New Zealand ensures safe food by
developing effective food standards for Australia and New
Zealand. It provides information on national food policy, food
safety issues and standards for food safety regulation:
www.foodstandards.gov.au
OzFoodnet is a health network to enhance the surveillance of
foodborne diseases in Australia and is funded by the Federal
Health Department. It provides reports on sporadic foodborne
disease, outbreaks and special research initiatives:
www.ozfoodnet.org.au
15 April 2005 | Australian Doctor |
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How to treat – foodborne illness
Background
DR MARTINE WALKER
Mosman, NSW
MAYA, a 37-year-old banker
who is eight weeks’ pregnant,
had eaten at a friend’s place
two days earlier — a light
cold lunch of deli products
(prosciutto, cheese, bread)
and fruit. Since that time she
had been nauseated and
feverish intermittently but
had no diarrhoea.
This was a very precious
IVF first pregnancy, and
Maya was very well informed
of all possible problems that
could impact on her baby’s
health. She was concerned
she may have listeriosis and
asked to be tested for this
infection.
Apart from a low-grade
temperature of 37.8˚C and
pulse of 90, her general and
abdominal examinations
were normal. Urinalysis was
also normal. I felt that listeriosis was very unlikely but I
was also keen to alleviate her
strongly expressed fears. I
was also unsure about the
best tests to exclude listeria
in order to reassure her.
Questions for the author
How likely is this illness to
be listeriosis and what is the
usual presentation of Listeria food poisoning?
Because listeriosis is a very
uncommon disease, it is an
unlikely cause of this
patient’s illness. Also, it is
more common after 26
weeks’ gestation because of
declining cell-mediated
immunity. Other more
common pathogens that produce nausea and fever, such
as viral pathogens, are more
likely causes.
How should Maya be best
investigated?
No further investigations
for listeriosis should be conducted on this patient unless
there is a suggestion of sepsis
or fetal complications. A
blood culture is unlikely to
be positive, given the presentation, and the finding of Listeria monocytogenes in stool
alone is not indicative of
invasive infection and not an
indication for antibiotic treatment.
Can you describe the risks of
listeria infection for a pregnant woman?
We know that people eat
listeria-contaminated food
regularly, probably many
times a year, yet there are
only about 70 cases identified a year in Australia. Usually fewer than 30% of these
How To Treat Quiz
Foodborne illness — 15 April 2005
1. Which ONE statement about foodborne
illnesses is correct?
❏ a) The three most common causes of
foodborne disease outbreaks in Australia are
Salmonella, Staphylococcus aureus and
norovirus
❏ b) Foodborne illnesses always occur within
48 hours of consumption of infected food
❏ c) Foodborne illnesses are not limited to
gastroenteritis
❏ d) Foodborne Illnesses are usually related to
protozoal infections in Australia
2. Rob, 24, works in the kitchen of an agedcare facility and developed vomiting and
diarrhoea 24 hours after a meal shared with
friends, some of whom have had similar
symptoms. Which of the listed infections is
he most likely to have (choose TWO)?
❏ a) Salmonella
❏ b) Norovirus
❏ c) Clostridium perfringens
❏ d) Hepatitis A
3. What are TWO features of a norovirus
infection?
❏ a) It always lasts less than 24 hours
❏ b) It can be detected on standard stool cultures
❏ c) The illness spreads rapidly
❏ d) It does not usually require hospital
admission
4. Norovirus infection is confirmed. What
advice should you give Rob about this
infection (choose ONE)?
❏ a) It is safe to return to work as soon as the
diarrhoea finishes
❏ b) When he returns to work he should pay
meticulous attention to hand washing
❏ c) There is no excretion of the virus in the
stool when the diarrhoea stops
❏ d) He will be immune to further infection by
norovirus
5. Joy, a 54-year-old high-school teacher,
has had diarrhoea for three days and is
admitted to hospital, where salmonella
septicaemia is diagnosed. Which ONE
statement about Joy’s management is
correct?
❏ a) A negative stool culture is necessary before
Joy returns to work
❏ b) Azithromycin 1g daily for three days is
appropriate
❏ c) Ciprofloxacin 500mg bd for 14 days is a
treatment of choice
cases will be pregnancy-associated so, despite the regular
exposure of pregnant women
to Listeria-contaminated
food, while the risk is higher
during pregnancy, their risk
is still very low.
In one study that followed
more than 500 pregnant
women with listeria in their
stool but who had no antibiotic treatment, all delivered
normal babies with no intercurrent listeria infection.
Is there an Australian listeriosis information sheet for
pregnant woman?
A brochure Listeria and
food. Advice for people at
risk is available at
www.foodstandards.gov.au/_
srcfiles/Listeria.pdf
General questions for the
author
According to your article,
only 10% of Giardia infection is foodborne. What are
the other important other
sources of Giardia infection.
Other risk factors for Giardia infection include contact
with animals and their faeces,
children in nappies, and
untreated water sources.
Test on stool specimens in
suspected giardia infection
are notoriously unreliable.
What are your suggestions
regarding optimising the likelihood of detecting Giardia?
About 85% of Giardia
infections can be diagnosed
with a single stool specimen.
Sensitivity increases with the
number of stool specimens
examined, so that three specimens collected every other
day over five days will detect
about 90% of infections.
However, some experts
recommend only two specimens be collected and, if
these test positive, a trial of
tinidazole could be considered.
How reasonable is it to treat
Giardia on speculation in the
context of what seems an
appropriate clinical picture?
It is common practice to
make a presumptive diagnosis of Giardia infection in the
context of diarrhoea lasting
more than seven days, and
particularly over several
weeks, with bloating and
abdominal cramps. In these
cases is reasonable to treat
with tinidazole.
What is the incidence of Giardia and Cryptosporidia infec-
tions from the water supply?
Waterborne disease surveillance is not yet as
advanced as foodborne disease surveillance in Australia
and more data are needed.
Infection from modern
municipal water supplies
with protection of the water
catchment and filtration is
very unlikely. The risk is
greater from rural sources
drawing water from less-protected water sources with
inadequate treatment, such
as rivers impacted by livestock.
What are the most common
microbiological causes of
food-related travellers’ diarrhoea?
A range of pathogens may
be implicated, including E
coli, viruses, salmonella,
campylobacter, shigella, giardia and Entamoeba histolytica.
How is travellers’ diarrhoea
best treated?
Avoidance of antibiotics is
recommended unless an invasive bacterial enteritis associated with sepsis is suspected.
Stool examination for parasites may lead to treatment
for Giardia or Entamoeba.
INSTRUCTIONS
Complete this quiz to earn 2 CPD points and/or 2 PDP points by marking the correct answer(s)
with an X on this form. Fill in your contact details and return to us by fax or free post.
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❏ d) The use of antibiotics may prolong the
excretion of salmonella
6. George, 40, is immunocompromised and
you are discussing good food hygiene
practices with him. Which advice is correct
(choose TWO)?
❏ a) The holding temperature for hot foods is
50˚C
❏ b) Food contact surfaces should be meticulously clean
❏ c) Avoid pasteurised milk
❏ d) Maintain clean hands
7. Which ONE food could George consider as
a lower-risk food?
❏ a) Food from salad bars
❏ b) Pressure cooked meal
❏ c) Chilled smoked seafood
❏ d) Soft cheese
8. Which TWO organisms have preformed
toxins in food that result in very short
incubation periods?
❏ a) Campylobacter
❏ b) Bacillus cereus
❏ c) Staphylococcus aureus
❏ d) Clostridium perfringens
ONLINE
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for immediate feedback
9. Which ONE statement about foodborne
infection is correct?
❏ a) Neurological manifestations are common
with norovirus infection
❏ b) Salmonellosis is usually associated with
diarrhoea and no abdominal pain
❏ c) Diarrhoea for more than a week with
minimal systemic symptoms suggests
parasitic infection
❏ d) Scombroid poisoning is associated with
temperature reversal
10. GPs have a legal obligation to report
foodborne outbreaks. Which ONE statement
about reporting is incorrect?
❏ a) Gastroenteritis in two members of a family
affected after sharing a common meal should
always be reported
❏ b) By reporting the outbreak, the health
department becomes responsible for
exploring the link
❏ c) Gastroenteritis in two or more people from
different households affected who have
shared a common meal should always be
reported
❏ d) Salmonellosis was the common cause of
outbreaks detected by state health
departments between 1980 and 2003
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HOW TO TREAT Editor: Dr Lynn Buglar
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Address: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Postcode: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The mark required to obtain points is 80%. Please note that some questions have more than one correct answer. Your CPD activity will be updated on your RACGP records every January, April, July and October.
NEXT WEEK The next How to Treat looks at UTIs in children. The author is Dr Patrina Caldwell, centre for kidney research, NHMRC centre of clinical research excellence in renal medicine,
The Children’s Hospital at Westmead, NSW; and lecturer, discipline of paediatrics and child health, University of Sydney.
46
| Australian Doctor | 15 April 2005
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