Salmonella, also called salmonellosis, is a foodborne illness named for the group of bacteria that cause it.
Salmonella causes diarrhea and gastroenteritis, and, rarely, typhoid fever. It is often spread through contaminated food or water. Raw or improperly prepared or stored foods such as beef, poultry, produce, raw milk and eggs can become contaminated with the salmonella bacteria. All foods, including vegetables, can potentially become contaminated. Contaminated foods usually look and smell normal. Cooking kills the bacteria.
The amount of salmonella bacteria needed to make a person ill depends on the type of bacteria, the number of bacteria ingested and the strength of a person’s defense systems. Acid secreted by the stomach to digest food is usually the body's first defense against salmonella. Bacteria that survive the stomach acid invade the walls of the small intestine and trigger a reaction by the immune system, the second line of defense. It takes a million or more bacteria to make someone in good health fall ill. A smaller number of bacteria can make a person ill, but it may take a longer time for the illness to develop. Usually, contaminated food contains more bacteria than contaminated water. Cheese and milk, antacids, H2 antagonists and antibiotics can decrease the amount of stomach acid, making it easier for the salmonella bacteria to make it out of the stomach to the intestine, where they can multiply. Chronic medical conditions such as lupus, diabetes, cancer or HIV make a person more vulnerable to salmonella. Young children and elderly adults, both of whom have weakened immune systems, also are at risk.
In severe salmonella infections, or in people with weakened immune systems, the bacteria can spread from the intestine to the bloodstream, a condition called bacteremia. This can cause an infection of blood vessels, heart (endocarditis), bones (osteomyelitis) or joints (septic arthritis).
Some people can become infected with salmonella but not fall ill. They become carriers of the disease -- able to pass it on to others without having symptoms of salmonella. Animals also can be carriers of salmonella. In an example reported in 2002 in the New England Journal of Medicine, a blood donor unwittingly passed on salmonella to two people. He had been infected by his snake. Neither the man nor the snake had symptoms of illness.
Snakes aren't the only animals that can harbor salmonella. Lizards, turtles, chicks and ducklings also are especially likely to pass salmonella to people. Dogs, cats, wild or pet birds, wild or pet rodents, horses and farm animals also can infect people. Salmonella has been found in the saliva of dogs and cats, so the bacteria can be transmitted by licking. Some pet foods made from animal products, such as pig ears, may be a source of salmonella for both dogs and the people who handle the foods.
Typhoid fever, which is also caused by salmonella bacteria, affects about 400 Americans each year, according to the Centers for Disease Control and Prevention (CDC). Most of these infections are acquired during international travel; typhoid fever is common in the developing world. Salmonella Typhi, the strain that causes typhoid fever, infects only humans. It can be transmitted by contaminated food or water. After recovering from typhoid fever, a few people become carriers. Antibiotics will cure both people who are carriers and those who have symptoms of infection.
Symptoms of gastroenteritis caused by salmonella usually begin six hours to three days after you are infected. These are the most common symptoms:
Loose stool or watery diarrhea that usually does not have blood; this usually lasts three to seven days
Fever of 100 to 102 degrees F that begins within two days of infection and usually lasts two days; a fever that lasts a week or more and increases daily suggests typhoid fever