Salmonella is a bacterium commonly found - and spread - through the feces of animals or people, often through unsanitary agriculture or food handling practices. Image Credit: Shutterstock

Washington: The US Food and Drug Administration earlier this week reported a widespread outbreak of salmonella food poisoning that sickened 73 people in 22 states, resulting in 15 hospitalisations. The cases have been linked to tainted bagged diced onions and celery made by the California company Gills Onions.

Salmonella is the most frequently reported cause of foodborne illness, according to the Department of Agriculture. It results in 1.35 million infections, 26,500 hospitalisations and 420 deaths annually in the United States - almost all of them from contaminated food - according to the Centers for Disease Control and Prevention.

What is salmonella? How can you prevent becoming ill from it? Here's what the experts say:

What causes salmonella?

Salmonella is a bacterium commonly found - and spread - through the feces of animals or people, often through unsanitary agriculture or food handling practices. It usually enters the food supply in the food chain: farming, industry, food inspectors, retailers, food service workers and even consumers themselves.

"Outbreaks are usually traced to contaminated foods, such as vegetables like jalapeo peppers that end up uncooked in guacamole, tomatoes and others," said Robert T. Schooley, an infectious diseases specialist at the University of California at San Diego. "Chicken and pork products are also places where salmonella can hang out."

In these cases, "they were usually contaminated in the fields where they were grown downstream from animal or human waste or the bacteria made it into food during handling by a food worker or a restaurant worker who was carrying salmonella in their GI tracts, with or without active disease," he added.

Food processing methods also can introduce bacterial contamination, "either by contaminated equipment, such as blades, knives or mixing vessels or by individuals handling the food and food products," said Brian Coombes, professor and chair of McMaster University's department of biochemistry and biomedical sciences.

"Oftentimes, processed foods have preservatives that extend the shelf life of the product, which could help amplify a bacterial contaminant in the product," Coombes said. "Some bacteria like salmonella can double every 20-30 minutes, so the longer the food is on the shelf, the more the bacterial contamination."

Salmonella also can be acquired from contact with reptiles such as lizards and snakes. "People who handle them or who eat with people who do are at increased risk of becoming infected," Schooley said. "Also, the organisms are sensitive to stomach acid, and people who are on antacids or proton pump inhibitors are at increased risk of infection."

Salmonella cases have exploded in the United States in recent years because of "the increased popularity of backyard chickens," said Dean Blumberg, chief of pediatric infectious diseases at the University of California Davis Health in Sacramento.

What can consumers do to prevent salmonella infection?

Cook your food: Salmonella are susceptible to heat and generally don't survive cooking, as long as the food reaches an internal temperature of 165 degrees Fahrenheit, experts said.

"In this case, thoroughly cooking the raw onions would likely have killed the salmonella, however, it is possible that even heat-destroyed bacteria could cause minor symptoms in some people," Coombes said. "Many foods linked to foodborne outbreaks are not cooked, including many types of vegetables that can be eaten raw."

Wash produce: Experts recommend washing all produce, although for some products that are consumed raw, "there is not much a consumer can do to minimize the risk of illness," DiCaprio said.

"Cooking is a good way to reduce the risk for all types of raw products," said Erin DiCaprio, associate professor in the department of food science and technology at the University of California at Davis. "We don't want to discourage consumption of fruits and vegetable because of the overall health benefit, but increasing awareness related to risks might help those at highest risk make informed decisions about what they purchase and how they prepare food."

Take precautions when preparing food: It's important to try to minimize cross-contamination during food preparation, which means separating raw poultry from other foods, and cleaning cutting boards and utensils with hot soapy water after contact with raw poultry, along with vigorous hand washing, experts said.

Don't forget the sink: Schaffner pointed out that many people wash their raw poultry before cooking. "Wash your hands thoroughly and rinse out the sink."

This is all especially important right now, "because Thanksgiving is almost upon us, and we soon will be preparing turkeys. So be mindful of that - and be careful," Schaffner said.

What are the symptoms of salmonella poisoning?

The symptoms can be nasty, but usually are self-limiting and not life-threatening. "I have taken care of patients with salmonella, and the vast majority of people recover, but it's a very unpleasant few days," said William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University.

Salmonella symptoms include fever, diarrhea, stomach cramps and sometimes vomiting. These can occur quickly after ingesting contaminated food products, within six hours, or take as long as six days before they appear, according to the CDC, usually lasting from four days to a week.

"Diarrhea causes water loss in the body, and so one danger is dehydration, which can be very serious," Coombes said. "Drinking plenty of clear fluids when symptoms are most active is important."

Some individuals, however, including the very young, the very old and those with compromised immune systems or other conditions, may be vulnerable to more serious illness. People who are immunocompromised, children under 5 and those with sickle cell disease "can have a more systemic infection including infection in their blood, bones and joints as well as other locations," said Lisa Speiser, an infectious diseases specialist at the Mayo Clinic in Phoenix.

People also can be "asymptomatic carriers," Speiser said.

How is it treated? When should you contact the doctor?

For uncomplicated cases - in otherwise healthy people - experts recommend against taking antibiotics. Treat the symptoms as you would any gastrointestinal upset, and drink plenty of fluids. Antibiotics should be reserved for the severely ill, they said.

"If you take antibiotics, your body may retain the bacterium for a longer period of time," Schaffner said, making that person a "carrier" of the organism. "Also, and of equal importance, treating uncomplicated salmonella gastroenteritis with antibiotics doesn't shorten the duration of illness, or is of any benefit. If you have any doubts whatsoever about the severity of your illness, call your doctor."

Coombes suggested patients seek medical care if the symptoms persist for longer than four days or if they can't tolerate fluids or foods.