S. aureus is a spherical bacterium (coccus) which on microscopic
examination appears in pairs, short chains, or bunched, grape-like
clusters. These organisms are Gram-positive. Some strains are capable of
producing a highly heat-stable protein toxin that causes illness in
aureus is a bacterium which is carried on the skin of 10% or more of the
population. In the majority of cases, this does not result in any harm.
Occasionally, recurrent skin infections (boils) can occur. Rarely
Staphylococcus aureus can cause a serious infection, such as pneumonia or
a blood stream infection.
Contact with wounds
and boils infected with Staphylococcus aureus can spread the infection.
with a person carrying the bacteria on their skin without symptoms and
sharing towels or linen, or inadequate laundering, can spread the
bacteria, particularly within families.
Lack of hand washing
during food preparation can result in Staphylococcus aureus from hands
contaminating food, which may lead to food poisoning.
infection range from pain, redness and swelling in an abscess, to a
serious illness with fever, and occasionally shock, in a blood stream
The diagnosis of
Staphylococcus aureus infection is made by growing the bacteria from a
sample of pus or blood.
In the majority of
cases, the infection can be successfully treated with a range of
antibiotics. In some cases, the bacteria are resistant to the commonly
used antibiotics. These bacteria are known as MRSA (methicillin resistant
Staphylococcus aureus). However, antibiotics are available which will work
Staphylococcus aureus (including MRSA) can be treated with appropriate
antibiotics. People who carry the germ on their skin or in their nose will
only require antibiotics under special circumstances.
Name of Acute Disease:
Staphylococcal food poisoning (staphyloenterotoxicosis;
staphyloenterotoxemia) is the name of the condition caused by the
enterotoxins which some strains of S. aureus produce.
Nature of the Disease:
The onset of symptoms in staphylococcal food poisoning is usually rapid
and in many cases acute, depending on individual susceptibility to the
toxin, the amount of contaminated food eaten, the amount of toxin in the
food ingested, and the general health of the victim. The most common
symptoms are nausea, vomiting, retching, abdominal cramping, and
prostration. Some individuals may not always demonstrate all the symptoms
associated with the illness. In more severe cases, headache, muscle
cramping, and transient changes in blood pressure and pulse rate may
occur. Recovery generally takes two days, However, it us not unusual for
complete recovery to take three days and sometimes longer in severe cases.
Infective dose--a toxin dose of less than 1.0 microgram in contaminated
food will produce symptoms of staphylococcal intoxication. This toxin
level is reached when S. aureus populations exceed 100,000 per
Diagnosis of Human Illness:
In the diagnosis of staphylococcal foodborne illness, proper interviews
with the victims and gathering and analyzing epidemiologic data are
essential. Incriminated foods should be collected and examined for
staphylococci. The presence of relatively large numbers of enterotoxigenic
staphylococci is good circumstantial evidence that the food contains
toxin. The most conclusive test is the linking of an illness with a
specific food or in cases where multiple vehicles exist, the detection of
the toxin in the food sample(s). In cases where the food may have been
treated to kill the staphylococci, as in pasteurization or heating, direct
microscopic observation of the food may be an aid in the diagnosis. A
number of serological methods for determining the enterotoxigenicity of
S. aureus isolated from foods as well as methods for the separation
and detection of toxins in foods have been developed and used successfully
to aid in the diagnosis of the illness. Phage typing may also be useful
when viable staphylococci can be isolated from the incriminated food, from
victims, and from suspected carrier such as food handlers.
Foods that are frequently incriminated in staphylococcal food poisoning
include meat and meat products; poultry and egg products; salads such as
egg, tuna, chicken, potato, and macaroni; bakery products such as
cream-filled pastries, cream pies, and chocolate eclairs; sandwich
fillings; and milk and dairy products. Foods that require considerable
handling during preparation and that are kept at slightly elevated
temperatures after preparation are frequently involved in staphylococcal
Staphylococci exist in air, dust, sewage, water, milk, and food or on
food equipment, environmental surfaces, humans, and animals. Humans and
animals are the primary reservoirs. Staphylococci are present in the nasal
passages and throats and on the hair and skin of 50 percent or more of
healthy individuals. This incidence is even higher for those who associate
with or who come in contact with sick individuals and hospital
environments. Although food handlers are usually the main source of food
contamination in food poisoning outbreaks, equipment and environmental
surfaces can also be sources of contamination with S. aureus. Human
intoxication is caused by ingesting enterotoxins produced in food by some
strains of S. aureus, usually because the food has not been kept
hot enough (60°C, 140°F, or above) or cold enough (7.2°C, 45°F, or below).
6. Frequency of Illness:
The true incidence of staphylococcal food poisoning is unknown for a
number of reasons, including poor responses from victims during interviews
with health officials; misdiagnosis of the illness, which may be
symptomatically similar to other types of food poisoning (such as vomiting
caused by Bacillus cereus toxin); inadequate collection of samples
for laboratory analyses; and improper laboratory examination. Of the
bacterial pathogens causing foodborne illnesses in the U.S. (127
outbreaks, 7,082 cases recorded in 1983), 14 outbreaks involving 1,257
cases were caused by S. aureus. These outbreaks were followed by 11
outbreaks (1,153 cases) in 1984, 14 outbreaks (421 cases) in 1985, 7
outbreaks (250 cases) in 1986 and one reported outbreak (100 cases) in
Death from staphylococcal food poisoning is very rare, although such
cases have occurred among the elderly, infants, and severely debilitated
All people are believed to be susceptible to this type of bacterial
intoxication; however, intensity of symptoms may vary.
Analysis of Foods:
For detecting trace amounts of staphylococcal enterotoxin in foods
incriminated in food poisoning, the toxin must be separated from food
constituents and concentrated before identification by specific
precipitation with antiserum (antienterotoxin) as follows. Two principles
are used for the purpose: (1) the selective adsorption of the enterotoxin
from an extract of the food onto ion exchange resins and (2) the use of
physical and chemical procedures for the selective removal of food
constituents from the extract, leaving the enterotoxin(s) in solution. The
use of these techniques and concentration of the resulting products (as
much as possible) has made it possible to detect small amounts of
enterotoxin in food.
There are developed rapid methods based on monoclonal antibodies (e.g.,
ELISA, Reverse Passive Latex Agglutination), which are being evaluated for
their efficacy in the detection of enterotoxins in food. These rapid
methods can detect approximately 1.0 nanogram of toxin/g of food.
10. Typical Outbreak:
1,364 children became ill out of a total of 5,824 who had eaten lunch
served at 16 elementary schools in Texas. The lunches were prepared in a
central kitchen and transported to the schools by truck. Epidemiological
studies revealed that 95% of the children who became ill had eaten a
chicken salad. The afternoon of the day preceding the lunch, frozen
chickens were boiled for 3 hours. After cooking, the chickens were deboned,
cooled to room temperature with a fan, ground into small pieces, placed
into l2-inch-deep aluminum pans and stored overnight in a walk-in
refrigerator at 42-45°F.
The following morning, the remaining ingredients of the salad were
added and the mixture was blended with an electric mixer. The food was
placed in thermal containers and transported to the various schools at
9:30 AM to 10:30 AM, where it was kept at room temperature until served
between 11:30 AM and noon. Bacteriological examination of the chicken
salad revealed the presence of large numbers of S. aureus.
Contamination of the chicken probably occurred when it was deboned. The
chicken was not cooled rapidly enough because it was stored in
l2-inch-deep layers. Growth of the staphylococcus probably occurred also
during the period when the food was kept in the warm classrooms.
Prevention of this incident would have entailed screening the individuals
who deboned the chicken for carriers of the staphylococcus, more rapid
cooling of the chicken, and adequate refrigeration of the salad from the
time of preparation to its consumption.
11. Atypical Outbreaks:
In 1989, multiple staphylococcal foodborne diseases were associated
with the consumption of canned mushrooms. (CDC Morbidity and Mortality
Weekly Report, June 23, 1989, Vol. 38, #24.)
Starkville, Mississippi. On February 13, 22 people became ill with
gastroenteritis several hours after eating at a university cafeteria.
Symptoms included nausea, vomiting, diarrhea, and abdominal cramps. Nine
people were hospitalized. Canned mushrooms served with omelets and
hamburgers were associated with illness. No deficiencies in food handling
were found. Staphylococcal enterotoxin type A was identified in a sample
of implicated mushrooms from the omelet bar and in unopened cans from the
Queens, New York. On February 28, 48 people became ill a median of 3
hours after eating lunch in a hospital employee cafeteria. One person was
hospitalized. Canned mushrooms served at the salad bar were
epidemiologically implicated. Two unopened cans of mushrooms from the same
lot as the implicated can contained staphylococcal enterotoxin A.
McKeesport, Pennsylvania. On April 17, 12 people became ill with
gastroenteritis a median of 2 hours after eating lunch or dinner at a
restaurant. Two people were hospitalized. Canned mushrooms, consumed on
pizza or with a parmigiana sauce, were associated with illness. No
deficiencies were found in food preparation or storage. Staphylococcal
enterotoxin was found in samples of remaining mushrooms and in unopened
cans from the same lot.
Philipsburg, Pennsylvania. On April 22, 20 people developed illness
several hours after eating food from a take-out pizzeria. Four people were
hospitalized. Only pizza served with canned mushrooms was associated with
illness. Staphylococcal enterotoxin was found in a sample of mushrooms
from the pizzeria and in unopened cans with the same lot number.