What is Salmonella?
It seems like every month we hear about another suspected outbreak of salmonella in the news. Salmonella is a bacterial infection that is passed to humans from animals, including poultry, cattle, pigs, and even domestic animals. Eating undercooked poultry and drinking unpasteurized milk are the most common ways humans can acquire the infection.
Recently the media has focused on vegetable products as the source of many Salmonella outbreaks. When vegetables or fruits are the source of an outbreak, it means that these products have been handled unsafely, such as processing or preparation on surfaces that have become contaminated with animal feces or raw poultry. Another way for vegetables to become contaminated is by an infected food handler.
The bacteria were first isolated by Theobald Smith in 1885 from pigs. The genus name Salmonella was derived from the last name of D.E. Salmon, who was Smith's director.
Salmonella (S.) is the genus name for a large number (over 2,500) of types of bacteria. Each type is distinctly identifiable by its specific protein coating, but they all are closely related. Salmonella bacteria are rod-shaped, flagellated, and are known to cause disease in humans, animals, and birds worldwide.
Salmonellosis, the name for gastroenteritis is characterized by nausea, vomiting, and diarrhea, is the most common disease caused by the organisms. Abdominal cramping usually occurs along with the other symptoms. Salmonellosis produces the symptoms that are commonly referred to as food poisoning. Even though food poisoning is usually a mild disease, nausea, vomiting, and diarrhea can lead to dehydration and even death and there are about 500 fatal cases per year in the U.S. It is important to note that many other organisms such as viruses and E. coli, and toxins like, botulism and pesticides can also produce symptoms similar to those of food poisoning. There are about 1.4 million cases of salmonellosis per year in the U.S., and other industrialized countries have similar rates. Countries with poor sanitation have a much higher incidence of salmonellosis.
Typhoid fever occurs when some of the Salmonella organisms (often identified as S. typhi) are not killed by the normal human immune defenses after they enter the gastrointestinal tract. Salmonella then survive and grow in the human spleen, liver, and other organs and may reach the blood. Salmonella can be shed from the liver to the gallbladder, where they can continue to survive and be secreted into the patient's feces for up to a year. Symptoms include high fevers up to 104 F, sweating, inflammation of the stomach and intestines, and diarrhea. Symptoms usually resolve, but many patients become Salmonella carriers. Approximately half of patients develop slow heartbeat, bradycardia, and about 30% of patients get flat, slightly raised red or rose-colored spots on the chest and abdomen. Typhoid fever is also referred to as enteric fever.
The Most Famous Case
Some Salmonella can survive in the cells of the immune system and can reach the bloodstream, causing a blood infection called bacteremia. Other Salmonella can enter the gallbladder, leaving the affected patient a chronic carrier of the organisms. Salmonella can then be shed with the bile from the gallbladder into the feces and then may infect other people. The most famous such carrier identified in 1907 was a cook named Mary Mallon, also known as "Typhoid Mary." She was suspected of infecting hundreds of individuals.
Antibiotics, often given intravenously, are needed to treat salmonellosis. Salmonella should be tested for antibiotic drug resistance as some Salmonella species have been reported to be resistant to multiple antibiotics. Resistance to drugs is a potential problem for those individuals that become infected with Salmonella as drug treatment options become limited.
Supportive therapy for both enteritis and enteric fevers consists mainly of preventing dehydration and electrolyte fluctuations, such as abnormal levels of potassium and sodium, with fluids containing electrolytes such as IV fluids or oral fluids like sports drinks.
Carriers of Salmonella are considered to be infected even though they may show no symptoms. Carriers can infect other people and need to be cured of the carrier state. About 85% of carriers can be cured by a combination of surgery to remove their gallbladder and antibiotic treatments.
Cleanliness is the most important aspect of prevention. Hand washing with soap and hot water, especially after handling eggs, poultry, and raw meat is likely to reduce the chance for infections. The use of antibacterial soaps has been recommended by some doctors and researchers. By using chlorine-treated drinking water, washed produce, and by not ingesting undercooked foods such as eggs, meat or other food, people can also reduce the chance of exposure to Salmonella. Avoiding direct contact with animal carriers of Salmonella like, turtles, snakes, other reptiles, and pigs may also prevent the disease.