One of the major causes of gastrointestinal food poisoning is caused by a species of bacteria called Salmonella. Salmonella bacteria are found worldwide in many types of animals. These animals carry the organism and spread it around, but generally do not become ill from it. When humans are exposed to large numbers of Salmonella, severe disease and even death can be the result. Most Salmonella infections are acquired by eating contaminated food, and can be prevented by proper handling and strict adherence to cooking guidelines. As a microbiologist for many years, I have seen many of these infections come across my bench. Let’s look at some of the most common types of food that can cause Salmonella infection as described in the textbook Medical Microbiology by Patrick R. Murray et.al.
Chicken and Eggs
Ingestion of contaminated chicken and eggs is a major cause of Salmonella infection in the United States. If chicken is cooked properly and thoroughly (to an internal temperature of 170 degrees F), the bacteria will be killed by the heat and unable to cause infection. Often times people don’t realize that cooking utensils that came into contact with the raw chicken can also act as a vehicle to transmit the disease. If one uses a knife or cutting board to prepare the chicken, then cuts raw vegetables to make a salad, enough viable bacteria can transferred to the vegetables which are being consumed raw. When preparing chicken, care must be taken to make sure that it is prepared separately from all other food items. Using wooden cutting boards for slicing raw chicken is also very dangerous. The bacteria can get into the grooves of the board, and if not washed properly, the cutting board can then become another vehicle for disease transmission. Spills or splashes from the raw chicken should also be cleaned up immediately using a dilute bleach solution, or some other type of appropriate disinfectant to make sure that a person can’t accidentally touch the counter surface and transmit the bacteria to themself.
Eggs are also largely to blame for Salmonella infection. When a chicken carries this bacteria, the eggs it lays can also harbor the organism. What some people don’t realize is that it is not only the outer shell that can be contaminated, but also the inner part of the egg itself. Eating eggs sunny side up, soft boiled, or any other way that doesn’t fully cook the yolk can cause infection. Eggs must be completely cooked at 145 degrees to kill the organism. Preparing a recipe that calls for raw eggs, such as eggnog, cesar dressing, or home made ice cream can also be hazardous. Bottom line, make sure anything that is prepared with raw eggs is cooked, or use some type of egg substitute that has already gone through a pasteurization process.
Cattle can also harbor Salmonella bacteria, and milk obtained from colonized cows can become contaminated during collection. Raw dairy products that haven’t been pasteurized are wonderful breeding grounds, and allow the Salmonella bacteria to multiply. So even one or two bacteria present in the milk can turn into thousands by the time it is consumed.
Raw fruits and Vegetables
Farmers sometimes use fecal material from many animals to fertilize their fields. Unfortunately, that “fertilizer” can be teeming with Salmonella. There has been alot of public anxiety recently regarding contaminated tomatoes, peppers, and other healthy vegetables, and these issues have cost the agricultural industry millions. Most crops are harvested and only superficially cleaned. When fresh vegetables are not washed sufficiently by the consumer, viable bacteria can remain on the surface. To make matters worse, if the food made with these vegetables (ie. fresh cole slaw or salsa) is not eaten right away, the bacteria can multiply creating a larger infectious dose when it is finally eaten. Word to the wise, clean your raw foods before you eat them, you never know what might be lurking.
Salmonella can also be transmitted in other ways. It is carried in the digestive tract of many animals that are kept as pets. Investigations have shown that reptiles are one of the biggest culprits. It is estimated that about 85% of all reptiles harbor this organism. People handling pet turtles, iguanas, and snakes have fell ill by neglecting to wash their hands after handling the animal. Dogs and cats have also been shown to carry the organism, but to a lesser extent.
How do you know if you have Salmonella? Signs and Symptoms
Generally, signs begin to show up about 12 hours to 3 days after infection. Symptoms tend to start with nausea and diarrhea, then progress over time into fever and abdominal cramping. Some patients also complain of chills and muscle aches during the illness. Most healthy individuals will recover in 4 to 10 days without any intervention, but in the case of people with altered immune systems the disease can become systemic and deadly. If the infection enters the bloodstream it can gain access to the surrounding tissues, and in severe cases, can even enter the brain and spinal cord. Treatment of a patient largely depends on their immune system. Fluid replacement and antidiarrheals are often used to keep the patient hydrated. In cases where the organism has gotten into the bloodstream, antibiotic intervention is often needed.