Salmonella infection is usually caused by eating raw or undercooked meat, poultry, eggs or egg products. The incubation period ranges from several hours to two days. Most salmonella infections can be classified as stomach flu (gastroenteritis). Possible signs and symptoms include:

• Nausea
• Vomiting
• Abdominal cramps
• Diarrhea
• Fever
• Chills
• Headache
• Blood in the stool

Signs and symptoms of salmonella infection generally last two to seven days. Diarrhea may last up to 10 days, although it may take several months before bowels return to normal.

A few varieties of salmonella bacteria result in typhoid fever, a sometimes deadly disease that is more common in developing countries.

Salmonella bacteria live in the intestines of people, animals and birds. Most people are infected with salmonella by eating foods that have been contaminated by feces. Commonly infected foods include:

• Raw meat, poultry and seafood. Feces may get onto raw meat and poultry during the butchering process. Seafood may be contaminated if harvested from contaminated water.
• Raw eggs. While an egg's shell may seem to be a perfect barrier to contamination, some infected chickens produce eggs that contain salmonella before the shell is even formed. Raw eggs are used in homemade versions of mayonnaise and hollandaise sauce.
• Fruits and vegetables. Some fresh produce, particularly imported varieties, may be hydrated in the field or washed during processing with water contaminated with salmonella. Contamination also can occur in the kitchen, when juices from raw meat and poultry come into contact with uncooked foods, such as salads.

The Food and Drug Administration also indicates that some salmonella outbreaks have been traced to contaminants in spices. The agency is seeking ways to increase the safety of spices.

Many foods become contaminated when prepared by people who don't wash their hands thoroughly after using the toilet or changing a diaper. Infection also can occur if you touch something that is contaminated, including pets, especially birds and reptiles, and then put your fingers in your mouth.

Factors that may increase your risk of salmonella infection include activities that may bring you into closer contact with salmonella bacteria and health problems that may weaken your resistance to infection in general.

Increased exposure

• International travel. Salmonella infection, including varieties that cause typhoid fever, is more common in developing countries with poor sanitation.
• Owning a pet bird or reptile. Some pets, particularly birds and reptiles, can carry salmonella bacteria.

Stomach or bowel disorders

Your body has many natural defenses against salmonella infection. For example, strong stomach acid can kill many types of salmonella bacteria. But some medical problems or medications can short-circuit these natural defenses. Examples include:

• Antacids. Lowering your stomach's acidity allows more salmonella bacteria to survive.
• Inflammatory bowel disease. This disorder damages the lining of your intestines, which makes it easier for salmonella bacteria to take hold.
• Recent use of antibiotics. This can reduce the number of "good" bacteria in your intestines, which may impair your ability to fight off a salmonella infection.

Immune problems

The following medical problems or medications appear to increase your risk of contracting salmonella by impairing your immune system.

• AIDS
• Sickle cell disease
• Malaria
• Anti-rejection drugs taken after organ transplants
• Corticosteroids

Salmonella infection usually isn't life-threatening. However, in certain people — especially infants and young children, older adults, transplant recipients, pregnant women, and people with weakened immune systems — the development of complications can be dangerous.

Dehydration

If you can't drink enough to replace the fluid you're losing from persistent diarrhea, you may become dehydrated. Warning signs include:

• Decreased urine output
• Dry mouth and tongue
• Sunken eyes
• Reduced production of tears

Bacteremia

If salmonella infection enters your bloodstream (bacteremia), it can infect tissues throughout your body, including:

• The tissues surrounding your brain and spinal cord (meningitis)
• The lining of your heart or valves (endocarditis)
• Your bones or bone marrow (osteomyelitis)
• The lining of blood vessels, especially if you've had a vascular graft

Reactive arthritis

People who have had salmonella are at higher risk of developing reactive arthritis. Also known as Reiter's syndrome, reactive arthritis typically causes:

• Eye irritation
• Painful urination
• Painful joints