Staphylococcal Food Poisoning

Staphylococcal food poisoning is a gastrointestinal illness. It is caused by eating foods contaminated with toxins produced by Staphylococcus aureus. It is one of the most common foodborne illnesses in the United States.^[1]

Signs and Symptoms

The onset of symptoms in staphylococcal food poisoning is usually rapid and in many cases severe, 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
• Abdominal cramps
• Prostration

Some people 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 is not unusual for complete recovery to take three days and sometimes longer in severe cases. Death from staphylococcal food poisoning is very rare, although such cases have occurred among the elderly, infants, and severely debilitated persons.

Colorized electron micrography of S. aureus. Source: CDC/ Janice Carr; Jeff Hageman.

Causes

Staphylococcal food poisoning is caused by eating food contaminated with Staphylococcus aureus. S. aureus is able to grow in a wide range of temperatures, pH (4.2 to 9.3) and sodium chloride (salt) concentrations. These characteristics enable S. aureus to grow in a wide variety of foods and conditions. Often this type of food poisoning occurs when cooked food is allowed to cool slowly and/or sit at room temperature for some time. The warm food allows the S. aureus bacteria to grow.

These bacteria produce a toxin — enterotoxin that remains in the food even when reheated. The symptoms are caused by the toxin not by the bacteria themselves, hence staphylococcal food poisoning is sometimes called food intoxication'.

Staphylococci are ubiquitous. These bacteria are present in air, dust, dirt, 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.^[2] The colonization rate is even higher for those who work with or who come in contact with sick individuals and hospital environments.

Staphylococcus enterotoxin

The pathogenic effects of Staphylococcus are mainly caused by toxins. In staph food intoxication, the major toxin is called an enterotoxin. The S. aureus enterotoxin causes quick onset food poisoning which can lead to cramps and severe vomiting. This enterotoxin is very stable and can withstand high temperatures (such as re-heating cooked food).

Diagnosis

The short incubation period, brevity of illness, and usual lack of fever help distinguish staphylococcal from other types of food poisoning except that caused by Bacillus cereus. Toxin-producing Staphylococcus aureus can be identified in stool or vomit, and toxin can be detected in food items. Diagnosis of staphylococcal food poisoning in an individual is generally based only on the signs and symptoms of the patient. Testing for the toxin-producing bacteria or the toxin is not usually done in individual patients. Testing is usually reserved for outbreaks involving several people.

Treatment

For most patients, staphylococcal food poisoning causes a brief illness. The best treatments for these patients are rest, plenty of fluids, and medicines to calm their stomachs. Highly susceptible people, such as the young and the elderly, are more likely to have severe illness requiring intravenous therapy and care in a hospital.

Antibiotics are not useful in treating this illness. The toxin is not affected by antibiotics.

Prevention

It is important to prevent the contamination of food with Staphylococcus before the toxin can be produced. S. aureus is often present on skin, under fingernails, in the nose and throat, in cuts, abrasions, boils, and abscesses. S. aureus can also be found on contaminated surfaces and food preparation utensils. The following can help prevent staphylococcal food poisoning:

• Washing hands and under fingernails vigorously with soap and water before handling and preparing food.
• Not preparing food if a person has a nose or eye infection.
• Not preparing or serving food for others if a person has wounds or skin infections on the hands or wrists.
• Keeping kitchens and food-serving areas clean and sanitized.
• Keeping hot foods hot (over 140°F) and cold foods cold (40°F or under). Especially if the food is stored for more than 2 hours.
• Storing cooked food in a wide, shallow container and refrigerating as soon as possible.

How Staphylococcal Food Poisoning is Spread

Although food handlers are usually the main source of contamination in food poisoning outbreaks, equipment and environmental surfaces can also be sources of S. aureus. Contaminated milk and cheeses can also contribute to the spread of the illness. Staphylococcus is salt tolerant and can grow in salty foods like ham. As the germ multiplies in food, it produces toxins that can cause illness. Staphylococcal toxins are resistant to heat and cannot be destroyed by cooking. Foods at highest risk of contamination with S. aureus and subsequent toxin production are those that are made by hand and require no cooking. Some examples of foods that have caused staphylococcal food poisoning are sliced meat, puddings, some pastries and sandwiches.

People with this illness are not contagious. Toxins are not transmitted from one person to another.

Epidemiology

Incidence

The true incidence of staphylococcal food poisoning is unknown for a number of reasons, including poor responses from sick people 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 analysis; and improper laboratory examination.

Outbreaks

In September, 1997, an outbreak of staphylococcal food intoxication, likely from cooked ham, occurred at a retirement party in Texas; over 30 people became ill. Although, the ultimate source of Staphylococcus aureus was not determined, a reconstruction of the preparation of the food reveals opportunities for S. aureus to grow and produce toxins.

The sequence of events follows: On September 25, a food preparer had purchased a 16-pound precooked packaged ham, baked it at home at 400 F (204 C) for 1.5 hours, and transported it to her workplace, a large institutional kitchen, where she sliced the ham while it was hot on a commercial slicer. The food preparer reported having no cuts, sores, or infected wounds on her hands. All 16 pounds of sliced ham had been placed in a 14-inch by 12-inch by 3-inch plastic container that was covered with foil and stored in a walk-in cooler for 6 hours, then transported back to the preparer's home and refrigerated overnight. The ham was served cold at the party the next day, when people ate it and subsequently became ill.

Staphylococcal toxins and bioterrorism

Staphylococcal toxins could potentially be used as a biological agent either by contamination of food/water or by aerosolization and inhalation. Breathing in low doses of staphylococcal enterotoxin B may cause fever, cough, difficulty breathing, headache, and some vomiting and nausea. High doses of the toxin have a much more serious effect

References

1. ↑ CDC, Outbreak of Staphylococcal Food Poisoning Associated with Precooked Ham -- Florida, 1997. MMWR December 19, 1997 / 46(50);1189-1191 Full Text
2. ↑ FDA, Center for Food Safety and Applied Nutrition, Bad Bug Book. Staphylococcus

External Links

FDA, Bad Bug Book: Staphylococcus