SALMONELLA

Salmonella is the common name given to a type of food poisoning caused by the bacteria Salmonella enteritidis (other types of illnesses are caused by other species of Salmonella bacteria, including typhoid fever. When people eat food contaminated by S. enteritidis, they suffer gastroenteritis (inflammation of the stomach and intestines, with diarrhea and vomiting).

Salmonella food poisoning is most often caused by improperly handled or cooked poultry or eggs. Because chickens carrying the bacteria do not appear ill, infected chickens can lay eggs or be used as meat.

Early in the study of Salmonella food poisoning, it was thought that Salmonella bacteria were only found in eggs which had cracks in them, and that the infecting bacteria existed on the outside of the eggshell. Stringent guidelines were put into place to ensure that cracked eggs do not make it to the marketplace, and to make sure that the outside of eggshells were all carefully disinfected. However, outbreaks of Salmonella poisoning continued. Research then ultimately revealed that, because the egg shell has tiny pores, even uncracked eggs which have been left for a time on a surface (such as a chicken's roost) contaminated with Salmonella could become contaminated. Subsequently, further research has demonstrated that the bacteria can also be passed from the infected female chicken directly into the substance of the egg prior to the shell forming around it.

Currently, the majority of Salmonella food poisoning occurs due to unbroken, disinfected grade A eggs, which have become infected through bacteria which reside in the hen's ovaries. In the United States, he highest number of cases of Salmonella food poisoning occur in the Northeast, where it is believed that about one out of 10,000 eggs is infected with Salmonella.

The most effective way to avoid Salmonella poisoning is to properly cook all food which could potentially harbor the bacteria. Neither drying nor freezing are reliable ways to kill Salmonella. While the most common source for human infection with Salmonella bacteria is poultry products, other carriers include pets such as turtles, chicks, ducklings, and iguanas. Products containing animal tissues may also be contaminated with Salmonella.

While anyone may contract Salmonella food poisoning from contaminated foods, the disease proves most threatening in infants, the elderly, and individuals with weakened immune systems. People who have had part or all of their stomach or spleen removed, as well as individuals with sickle cell anemia, cirrhosis of the liver, leukemia, lymphoma, malaria, louse-borne relapsing fever, or acquired immunodeficiency syndrome (AIDS) are particularly susceptible to Salmonella food poisoning. In the United States, about 15% of all cases of food poisoning are caused by Salmonella.

Salmonella food poisoning occurs most commonly when people eat undercooked chicken or eggs, sauces, salad dressings, or desserts containing raw eggs. The bacteria can also be spread if raw chicken, for example, contaminates a cutting board or a cook's hands, and is then spread to some other uncooked food. Cases of Salmonella infections in children have been traced to the children handling a pet (such as a turtle or an iguana) and then eating without first washing their hands. An individual who has had Salmonella food poisoning will continue to pass the bacteria into their feces for several weeks after the initial illness. Poor handwashing can allow others to become infected.

Symptoms of Salmonella food poisoning generally occur about 12–72 hours after ingestion of the bacteria. Half of all patients experience fever; other symptoms include nausea, vomiting, diarrhea, and abdominal cramping and pain. The stools are usually liquid, but rarely contain mucus or blood. Diarrhea usually lasts about four days. The entire illness usually resolves itself within about a week.

While serious complications of Salmonella food poisoning are rare, individuals with other medical illnesses are at higher risk. Complications occur when the Salmonella bacteria make their way into the bloodstream. Once in the bloodstream, the bacteria can invade any organ system, causing disease. Infections which can be caused by Salmonella include: bone infections (osteomyelitis), infections of the sac containing the heart (pericarditis), infections of the tissues which cover the brain and spinal cord (meningitis), and liver and lung infections.

Salmonella food poisoning is diagnosed by examining a stool sample. Under appropriate laboratory conditions, the bacteria in the stool can be encouraged to grow, and then processed and viewed under a microscope for identification.

Simple cases of Salmonella food poisoning are usually treated by encouraging good fluid intake, to avoid dehydration. Although the illness is caused by a bacteria, studies have shown that using antibiotics may not shorten the course of the illness. Instead, antibiotics may have the adverse effect of lengthening the amount of time the bacteria appear in the feces, thus potentially increasing others' risk of exposure to Salmonella. Additionally, some strains of Salmonella are developing resistance to several antibiotics.

Efforts to prevent Salmonella food poisoning have been greatly improved now that it is understood that eggs can be contaminated during their development inside the hen. Flocks are carefully tested, and eggs from infected chickens can be pasteurized to kill the bacteria. Efforts have been made to carefully educate the public about safe handling and cooking practices for both poultry and eggs. People who own pets that can carry Salmonella are also being more educated about more careful handwashing practices. It is unlikely that a human immunization will be developed, because there are so many different types of Salmonella enteritidis. However, researchers in 1997 produced an oral vaccine for poultry from genetically altered live Salmonella bacteria, currently undergoing testing, that may show the prevention of Salmonella bacteria from infecting meat or eggs. In 2001, two teams of researchers in England sequenced the genomes of both Salmonella Typhimurium (a common cause of food poisoning) and Salmonella Typhi the cause of typhoid fever). Data gathered from the project will improve diagnosis of Salmonella infections, and may eventually lead to a method of blocking its transmission in humans.