Salmonella Food Poisoning (Encyclopedia of Medicine)
Salmonella food poisoning is a bacterial food poisoning caused by the Salmonella bacterium. It results in the swelling of the lining of the stomach and intestines (gastroenteritis). While domestic and wild animals, including poultry, pigs, cattle, and pets such as turtles, iguanas, chicks, dogs, and cats can transmit this illness, most people become infected by ingesting foods contaminated with significant amounts of Salmonella.
Salmonella food poisoning occurs worldwide, however it is most frequently reported in North America and Europe. Only a small proportion of infected people are tested and diagnosed, and as few as 1% of cases are actually reported. While the infection reate may seem relatively low, even an attack rate of less than 0.5% in such a large number of exposures results in many infected individuals. The poisoning typically occurs in small, localized outbreaks in the general population or in large outbreaks in hospitals, restaurants, or institutions for children or the elderly. In the United States, Salmonella is responsible for about 15% of all cases of food poisoning.
Improperly handled or undercooked poultry and eggs are the foods which most frequently cause Salmonella food poisoning. Chickens are a major carrier of Salmonella...
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Salmonella Food Poisoning (Encyclopedia of Children's Health)
Salmonella food poisoning is a bacterial infection that causes inflammation (swelling) of the lining of the stomach and intestines (gastroenteritis). The causative bacteria is called Salmonella. While domestic and wild animals, including poultry, pigs, cattle, and pets such as turtles, iguanas, chicks, dogs, and cats can transmit this illness, most people become infected by ingesting foods contaminated with significant amounts of the causative bacteria.
Improperly handled or undercooked poultry and eggs are the foods which most frequently cause salmonella food poisoning. Chickens are a major carrier of salmonella bacteria, which accounts for its prominence in poultry products. However, identifying foods which may be contaminated with salmonella is particularly difficult because infected chickens typically show no signs or symptoms. Since infected chickens have no identifying characteristics, these chickens go on to lay eggs or to be used as meat.
At one time, it was thought that salmonella bacteria were only found in eggs which had cracked, thus allowing the bacteria to enter. Ultimately, it was learned that, because the egg shell has tiny pores, even uncracked eggs which sat for a time on...
(The entire section is 1400 words.)
Salmonellosis (Encyclopedia of Public Health)
Salmonellosis is a common enteric disease caused by rod-shaped, gram-negative bacteria. The name is derived from the American veterinary surgeon, Daniel A. Salmon, who described Salmonella choleraesuis as the cause of hog cholera in 1885. Since then over 2,200 Salmonella serotypes have been described; each is distinguished by its unique combination of cell wall, flagella, and capsular antigens. Many serotypes are further subdivided, usually for epidemiological studies, by their sensitivity to standard sets of bacteriophages (phage typing), and DNA fingerprinting methods. Salmonella are found in the intestinal tract of animals and birds, including domestic species (e.g., cattle, poultry), wild animals, and pets. Most human infections are caused by a few serotypes, commonly S. typhimurium and S. enteritidis. In most countries that keep national statistics, the majority of human cases are due to only five to ten common serotypes.
Salmonellosis is characterized by diarrhea, headache, abdominal pain, fever, and vomiting, beginning 6 to 72 hours (usually 6 to 36 hours) after infection. Healthy people normally recover within a week. Some individuals, however, are more susceptible to serious illness (see Table 1), and there is increasing evidence of longer-term sequelae occurring in a small proportion of cases.
Specific Salmonella serotypes are adapted to specific hosts, in which they usually cause septicaemia. For example, Salmonella typhi, is the cause of typhoid in man. Human infection is linked to a diverse variety of foods, possibly contaminated by animal or human feces during slaughter or during cultivation, harvesting, and preparation. Foods most commonly linked to illness include those of animal origin, such as meat products, unpasteurized milk, poultry, and eggs; foods contaminated during cultivation or preparation including vegetables, salads, fruit; and, less commonly, processed foods such as chocolate and snack products. Human infection has also been linked to exotic pets such as turtles, reptiles, and small mammals. People recovering from infection or with mild symptoms excrete salmonellae in their feces, and they may become a source of infection for others. Person-to-person spread is a particular risk where hygiene standards are difficult to maintain, as in institutions, day-care facilities, nursing homes, and households with ill individuals.
Most cases are apparently sporadic, though outbreaks occurring in the general population are not unusual and may be linked to a social event or institution such as a hospital or nursing home, or large-scale catering issues such as hotels, restaurants, and canteens. More rarely, large national and international outbreaks have been associated with manufactured or processed food productsn 1998 over 800 cases of S. enteritidis in Canada were associated with a pre-packed lunch product. Probably the largest recorded Salmonella outbreak affected an estimated 185,000 individuals who drank improperly pasteurized milk in the United States in 1985. It is recognized that even in countries which keep national statistics most cases are not reported. For example, only an estimated 1
|Individuals Susceptible to Severe Disease or Complications|
|Susceptible Individuals||Possible Complication|
|SOURCE: Courtesy of author.|
|Very young and elderly.||Rapid and severe dehydration.|
|Individuals with low stomach acid.||Increased susceptibility to infection.|
|Individuals with cancers and depressed immune systems, including HIV-infected persons.||Increased risk of Salmonella septicaemia.|
|Individuals with sickle-cell disease.||Risk of internal abscesses and bone-joint infections.|
percent of cases in the United States are reported, and the estimated morbidity and economic burden is high. Current public health concern centers around the emergence of multiple antibiotic resistant salmonellae, which make serious illness, such as blood infection, difficult to treat.
PAUL N. SOCKETT
(SEE ALSO: Food-Borne Diseases)
Old, D. C. (1992) "Nomenclature of Salmonella." Journal of Medical Microbiology 37:36163.
Roberts, J. A., and Sockett, P. (1994) "The Socioeconomic Impact of Human Salmonella Enteritidis Infections." International Journal of Food Microbiology 21:11729.
Rodrigue, D. C.; Tauxe, R. V.; and Rowe, B. (1990). "Increase in Salmonella Enteritidis: A New Pandemic?" Epidemiology and Infection 1:217.
Saeed, A. M.; Gast, R. K.; Potter, M. E.; and Wall, P. G., eds. (1999). Salmonella enteritidis serovar enteritidis in Humans and Animals: Epidemiology, Pathogenesis, and Control. Ames, IA: Iowa State University Press.
Sockett, P. N. (1991). "The Economic Implications of Human Salmonella Infection." Journal of Applied Bacteriology 71:28995.
Salmonella Food Poisoning (World of Microbiology and Immunology)
Salmonella food poisoning, consistent with all food poisoning, results from the growth of the bacterium in food. This is in contrast to food intoxication, were illness results from the presence of toxin in the food. While food intoxication does not require the growth of the contaminating bacteria to reasonably high numbers, food poisoning does.
Salmonella is a Gram negative, rod-shaped bacterium. The gastrointestinal tracts of man and animals are common sources of the bacterium. Often the bacterium is spread to food by handling the food with improperly washed hands. Thus, proper hygiene is one of the keys to preventing Salmonella food poisoning.
The food poisoning caused by Salmonella is one of about ten bacterial causes of food poisoning. Other involved bacteria are Staphylococcus aureus, Clostridium perfringens, Vibrio parahaemolyticus, and certain types of Escherichia coli. Between 24 and 81 million cases of food borne diarrhea due to Salmonella and other bacteria occur in the United States each year. The economic cost of the illnesses is between 5 and 17 billion dollars.
Poultry, eggs, red meat, diary products, processed meats, cream-based desserts, and salad-type sandwich filling (such as tuna salad or chicken salad) are prime targets for colonization by species of Salmonella. The high protein content of the foodstuffs seems to be one of the reasons for their susceptibility. Contamination is especially facilitated if improperly cooked or raw food is held at an improper storage temperature, for example at room temperature. Proper cooking and storage temperatures will prevent contamination, as Salmonella is destroyed at cooking temperatures above 150° F (65.5 °C) and will not grow at refrigeration temperatures (less than 40°F, or 4.4°C). Also, contamination can result if the food is brought into contact with contaminated surfaces or utensils.
The vulnerable foods offer Salmonella a ready source of nutrients and moisture. If the temperature conditions are right for growth, the increase in numbers of Salmonella can be explosive. For example, from a starting population of a single live bacterium with a division time of 30 minutes, a population of over 500 million bacteria can be generated in just 15 hours.
The ingestion of contaminated foods leads, within hours, to the development of one or all of the following ailments: stomach cramps, vomiting, fever, headache, chills, sweating, fatigue, loss of appetite, and watery or bloody diarrhea. Prolonged diarrhea is dangerous, as the body can be depleted of fluids and salts that are vital for the proper functioning of organs and tissues. The resulting shock to the body can be intolerably lethal to infants and the elderly. As well, there is a possibility that the bacteria can spread from the intestinal tract to the bloodstream, leading to infections in other parts of the body.
There are hundreds are different forms, or strains, of Salmonella, varying in the antigenic composition of their outer surface and in the maladies caused. Concerning food poisoning, Salmonella enteriditis is of particular concern. This strain causes gastroenteritis and other maladies because of several so-called virulence factors the organism is armed with.
One virulence factor is called adhesin. An adhesin is a molecule that functions in the recognition and adhesion of the bacterium to a receptor on the surface of a host cell. In the case of Salmonella, the tube-like structures called fimbriae can perform this function. Other molecules on the surface of the bacterium can be involved also.
Another virulence factor is a compound called lipopolysaccharide (LPS for short). Depending on the structure, LPS can help shield the Salmonella surface from host antibacterial compounds. As well, part of the LPS, can lipid A, can be toxic to the host. The lipid A toxic component is also referred to as endotoxin. Salmonella also produces another toxin called enterotoxin. Other bacteria produce enterotoxin as well. The Salmonella enterotoxin is readily degraded by heat, so proper cooking of food will destroy the activity of the toxin. The enterotoxin remains inside the bacteria, so the toxin concentration increases with the increase in bacterial numbers.
Salmonella is not particularly difficult to identify, as it produces distinctive visual reactions on standard laboratory growth media. For example, on bismuth sulfide media the bacteria produce hydrogen sulfide, which produces jet-black colonies. Unfortunately for the individual who experiences a food poisoning event, the diagnosis is always "after the fact." Knowledge of the cause often comes after the miseries of the poisoning have come and gone. But, in those instances where the spread of the bacteria beyond the gastrointestinal tract has occurred, diagnosis is helpful to treat the infection.
The prospects of eliminating of Salmonella food poisoning using vaccination are being explored. The most promising route is to block the adhesion of the bacteria to host epithelial cells of the intestinal tract. Such a strategy would require the development of a vaccine with long lasting immunity. However, vaccine development efforts will likely be devoted to other illnesses. For the foreseeable future, the best strategy in preventing Salmonella food poisoning will remain the proper cooking of foods and the observance of good hygiene practices when handling food.
See also Food preservation