“The Big 6” foodborne pathogens: Salmonella

What you need to know about the foodborne pathogen, Salmonella, and how to prevent it.

Salmonella is a group of bacteria that includes about 2500 different strains worldwide. For the purposes of this article we are going to talk about two groups of this bacteria- typhoidal (S. typhi) and non-typhoidal (salmonella spp.). Similar to our last bacteria, shigella, the salmonella family shares about 65 percent of their DNA with E. coli.

The name salmonella has nothing to do with salmon or fishing. In fact, it is named after the American scientist, Daniel Salmon, who first identified the bacteria in the 1800s, despite the fact that the bacteria had probably inhabited America, and made people ill, since the 1600s. Today there are about 5,700 cases of S. typhi and 140,000 cases of S. spp each year in the U.S.

Common sources and transmission

Salmonella typhi is transmitted person-to-person or from consuming water that is contaminated with sewage. It is actually a pretty rare disease in the U.S. and over 75 percent of cases in Americans are acquired during travel to foreign countries where the disease is more prevalent. Mary Mallon, more commonly known as “Typhoid Mary,” brought attention to the disease in the early 1900s when she worked as a cook for 7 different families in New York City, almost all of whom eventually came down with the illness. Mary, however, never had a single symptom and it was then discovered that a person could be a “carrier” for the disease and pass it on to others unknowingly. The most common vessel in the U.S. is beverages or ready-to-eat foods that were handled by infected persons or through water contaminated by human feces. S. typhi is one of the few food-borne diseases that only infects humans and is not passed by other animals.

The majority of the other common Salmonella species usually have poultry or eggs as their vector of transmission. Eating undercooked eggs or poultry or not properly cleaning after handling these items can lead to bacterial growth and infection. Although poultry is the most common source, that does mean it isn’t found in other foods like cheese and peanut butter, both of which have been involved in Salmonella-related food recalls in the last decade. Salmonella is also found on the skin of reptiles, which can then be passed on via food handled by dirty hands.

Symptoms and duration

S. typhi

  • Sustained fever of up to 104 degrees Fahrenheit
  • Weakness, stomach pains, headache, loss of appetite
  • Symptoms may not appear until up to 3 weeks after exposure and can last up to 60 days

Non-typhoidal salmonella

  • Also referred to as salmonellosis
  • Diarrhea, sometimes bloody
  • Sometimes fever, cramps, vomiting, body aches
  • Symptoms occur 6-72 hours after exposure and can last 3-7 days
  • Can cause reactive arthritis that can last days or years after other symptoms have ceased
Prevention
  • Wash hands before preparing food, and after handling meat or eggs
  • Cook meat and eggs to proper minimum internal temperatures
  • Do not eat foods containing raw or undercooked eggs, or unpasteurized milk
  • Avoid cross contamination by keeping raw or undercooked foods away from foods that will not be further cooked

For more information regarding salmonella check out the “It was probably something you ate” by Nichols Fox ad “Food, Sex, and Salmonella: Why Our Food is Making Us Sick” by David Waltner-Toews. Check back later this week to learn more about the Big 6 Pathogens from Michigan State University Extension.

Other articles in this series

Related Events

Related Articles

Related Resources