Integrity
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Integrity
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SYNONYMS:Staphylococcal alimentary toxicosis, staphylococcal gastroenteritis. ETIOLOGY:Coagulase-positive strains of Staphylococcus aureus that produce enterotoxins. Very few coagulase-negative stains are enterotoxigenic. The toxin is preformed in the food involved. To date, six types of enterotoxins are known: A, B, C, D, E, and F; of these A is the most prevalent in outbreaks. Enterotoxin F is implicated in toxic shock syndrome (TSS). Some strains can produce two or even three different enterotoxins. The toxins are heat-resistant and can withstand a temperature of 100oC for 30 minutes. GEOGRAPHIC DISTRIBUTION:Worldwide. THE DISEASE IN MAN:The incubation period is short, generally 3 hours after ingestion of the food involved. The interval between consumption of the enterotoxin and the first symptoms can vary from 30 minutes to 8 hours, depending on the quantity of toxin ingested and the susceptibility of the individual. The major symptoms are nausea, vomiting, abdominal pains, and diarrhea. Some patients may show low pyrexia (up to 38º C). More serious cases manifest prostration, cephalalgia, abnormal temperature, and lowered blood pressure, as well as blood and mucus in the stool and vomit. The course of the disease is usually benign and the patient recovers without medication in 24 to 72 hours. Recently, a toxic shock syndrome has been described. Symptoms consist of vomiting, diarrhea, high fever, erythroderma, edema, renal insufficiency, and toxic shock. Most patients are women who become ill during their menstrual period. The above-described symptoms also are observed in association with abscesses and osteomyelitis caused by S. aureus. A staphylococcal enterotoxin designated F was isolated from 94% of these patients strains of S. aureus from nine patients with toxic shock were examined, and production of enterotoxin F was confirmed in eight of them; only 42% of 50 strains isolated from other hospitalized patients produced this toxin. Toxin F production was not found in 48 strains originating from animal clinical specimens. Of 24 strains from healthy human carriers, 25% produced the toxin. SOURCE OF INFECTION AND MODE OF TRANSMISSION:The principal reservoir of is S. aureus is the human carrier. A high proportion (from 30 to 35%) of healthy humans have staphylococci in the nasopharynx and on the skin. A carrier with a respiratory disease can contaminate foods by sneezing coughing, or expectorating. Similarly, he may contaminate foods he handles if he has a staphylococcal skin lesion. However. even if not sick himself, the carrier may spread the agent by handling food ingredients, utensils, and equipment, or the finished food product. According to different authors, the proportion of enterotoxin-producing S. aureus strains of human origin varies between 18 and 75%. The proportion of toxigenic strains isolated from various sources (human, animal, and food) is very high. Strains of human origin predominate in epidemics, but animals are also reservoirs of the infection. Milk from cow udders infected with staphylococci can contaminate numerous milk products. Many outbreaks have been produced by consumption of inadequately refrigerated raw milk or cheeses from cows whose udders harbored staphylococci. The largest outbreak affected at least 500 students in California between 1977 and 1981 and was traced to chocolate milk. In developing countries, where refrigeration after milking is often inadequate, milk and milk products may be an important source of staphylococcal intoxication. According to recent investigations, a high proportion of strains isolated from staphylococcal mastitis produce enterotoxin A, which causes many outbreaks in humans. In several investigations it was possible to isolate from skin lesions and cow's milk the S. aureus phage type 80/81, which is related to epidemic infections in man. One of the studies proved that phage type 80/81 produced interstitial mastitis in cows. The same phage type was found among animal caretakers, which indicates that the bacterium is intertransmissible between man and animals and that the latter may reinfect man. Infected fowl and dogs may also give rise to and be a source of staphylococcal poisoning in man. One subject that deserves special attention is the appearance of antibiotic-resistant strains in animals whose food includes antibiotics. Concern exists over the possible transmission of these strains to man. On several occasions, resistant stains have been found both in animals (cows, swine, and fowl) and in their caretakers, with the same antibiotic resistance. Moreover, "human" strains (phage typed) have on occasion been isolated from the nostrils and lesions of other species of domestic animals. A variety of foods and dishes may be vehicles of the toxin. If environmental conditions are favorable, S. aureus multiplies in the food and produces enterotoxins. Once made, the toxin is not destroyed even if the food is subjected to boiling while being cooked. Consequently, the toxin may be found in the food whereas staphylococci are not. An important causal factor in food-borne intoxications is holding food at room temperature, which permits multiplication of staphylococci. Lack of hygiene in food handling is another notable factor. Frequently, outbreaks of food poisoning may be traced to a single dish. THE ROLE OF ANIMALS IN THE EPIDEMIOLOGY OF THE DISEASE:Most outbreaks are caused by human strains, and to a lesser degree by strains from cattle and other domestic animals. Animal products - such as meat, ham, milk, cheese, cream, and ice cream - usually constitute a good substrate for staphylococcal multiplication. Milk pasteurization offers no guarantee of safety if toxins were produced before heat treatment, as the toxins are heat-resistant. Outbreaks have been caused by reconstituted powdered milk, even when the dried product contained few or no staphylococci. DIAGNOSIS:The short incubation period between ingestion of contaminated food and appearance of symptoms is the most important clinical criterion. Laboratory confirmation, when possible, is based above all on demonstration of the presence of enterotoxin in the food. Biological methods (inoculation of cats with cultures of the suspect food, or of rhesus monkeys with the foodstuffs or cultures) are expensive and not always reliable. As substitutes, serologic methods such as immunodiffusion, immunofluorescence, hemagglutination inhibition, and, recently, ELISA are increasingly used. In febrile patients, blood cultures are indicated. Isolation of enterotoxigenic staphylococcal strains from foods and typing by phage or, more recently, by immunofluorescence have epidemiologic value. Quantitative examination of staphylococci in processed or cooked foods serves as an indicator of hygienic conditions in the processing plant and of personnel supervision. TREATMENT:In humans, treatment usually consists of replacement of fluids and electrolytes and, very rarely, management of hypovolemic shock and respiratory embarrassment. If botulism is suspected, polyvalent antitoxin must be administered. Historically, antimicrobial drugs have not been recommended unless a specific microbial agent producing progressive systemic involvement can be identified. Preliminary data now suggest that ciprofloxacin, 500 mg every 12 hours for 5 days, may shorten the duration of diarrhea and lead to a more rapid resolution of symptoms. Antimotility drugs may relieve cramping and decrease diarrhea in mild cases. Their use should be limited to patients without fever and without dysentery (bloody stools), and they should be used in low doses. CONTROL:It includes the following measures: a) education of persons who prepare food at home or commercially in proper personal hygiene; b) exclusion from handling food of individuals with abscesses or other skin lesions; and c) refrigeration of all foods to prevent bacterial multiplication and formation of toxins. Foods should be kept at room temperature as little time as possible. The veterinary milk inspection service should supervise dairy installations, ensuring that refrigeration units function correctly and are used immediately after milking, and that milk is refrigerated during transport to pasteurization plants. The veterinary meat inspection service should be responsible for enforcing hygienic regulations before and after slaughter as well as during handling and production of meat products. Control of hygienic conditions in meat retail establishments is also important. |
