By Barry C. Fox, M.D., University of Wisconsin
Infections of the gastrointestinal tract are generally caused by viruses, with viral gastroenteritis being the cause of 30 to 40 percent of diarrhea cases in the US. But viruses are not the only reason for illness in your gut. Parasites and bacterial infections cause a lot of trouble, too.
Parasites are nasty organisms that use your body for food and shelter. Giardia lamblia is the most common parasitic infection of humans. It’s also the most frequently isolated intestinal parasite in the United States, with about 20,000 cases annually. However, there are millions of cases of giardiasis worldwide annually.
Giardia symptoms appear a week or two after the ingestion of contaminated water. One additional notable symptom that may point to Giardia as a cause is flatulence. The Western and Northeastern mountain regions of the United States are areas where there is a high risk for acquiring Giardia.
Environmental factors, such as the closeness of the water supply to the habitat of a certain animal species, especially beavers, predispose the area to infestation with Giardia. In both infected humans and animals, both Giardia cysts and trophozoites are excreted and the cyst forms are infectious. Cysts are even resistant to chlorination, and can persist for months in soil or water.
Learn more about the dynamic world of infectious disease.
The 1993 Milwaukee Outbreak
In the spring of 1993 there was a widespread outbreak of acute watery diarrhea among the residents of Milwaukee. For two weeks no one could figure out what was causing it—checks for viruses and bacteria came up with nothing. Doctors suggested that patients drink more water and stay hydrated.
Then, at a fancy Sunday brunch, people noticed that the ice sculptures were actually cloudy. An investigation revealed there was increased turbidity of the water in one of the city’s treatment plants, and the plant was shut down.
Evidence of a parasite, Cryptosporidium, was identified in the Milwaukee water system during these weeks. It was estimated that 400,000 people had watery diarrhea attributable to this outbreak. There were 100 deaths in the elderly and other immune-compromised individuals. The 1993 Milwaukee Cryptosporidiosis outbreak was the largest waterborne disease outbreak in history.
So what happens when the diarrhea involves invasion of the intestines? The presence of white blood cells under the microscope and/or blood in bowel movements defines an inflammatory diarrhea, since the germ invades the intestinal lining. This shows up in bowel movements as the passage of diarrhea with blood or mucus, the presence of moderate or severe abdominal pain, and fever.
There is a wide array of harmful bacteria that cause these symptoms: Salmonella, Campylobacter, Shigella, and a special type of E. coli. Symptoms of all these bacterial diseases may begin as early as 12 hours but more typically at 48 to 72 hours after ingestion of contaminated food. The bacteria need time to multiply and produce their toxins.
This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now Wondrium.
Up to 2 million cases of Salmonella infection occur in the United States every year, with 98 percent of the contamination caused by bacteria linked to animal sources of food. Eggs at the grocery store appear to have intact shells, but approximately 1 in 1000 have cracks and contain Salmonella. When these eggs are used raw, such as in the dressing for Caesar salad or in eggs sunny-side up with runny yolks, Salmonella can contaminate the food.
Virtually every other month there is a CDC epidemiology report involving a Salmonella outbreak. For example, in 1994, a quarter of a million Americans developed intestinal illness after eating ice cream from a national brand where Salmonella contaminated the ice cream processing trucks.
Campylobacter has recently become the most common bacterial cause of intestinal illness in the United States—around 3 million annual cases, with 1 percent of the population affected. Seventy to eighty percent of retail poultry is contaminated by Campylobacter, thus making cross-contamination very hazardous in food preparation.
Using good handling techniques for poultry, such as not preparing your salad on the same cutting board as your chicken, will help reduce these risks.
Learn more about antibiotics.
Illness from E. coli
What about another invasive foodborne bacteria E. coli O157:H7? E. coli O157:H7 serotype was first identified as a cause of illness in 1982 during an outbreak of severe bloody diarrhea traced to contaminated hamburgers. This germ has since emerged as an important cause of both bloody diarrhea and an illness known as hemolytic-uremic syndrome, or HUS. HUS is the most common cause of acute kidney failure in children, and can occasionally result in childhood deaths.
In this outbreak, undercooking of hamburger patties likely played an important role. Based on this outbreak, the FDA made recommendations to increase the internal temperature for cooking hamburgers to 155 to 160 degrees Fahrenheit and these recommendations remain in place at the present time.
Nevertheless, certain traditions in the United States go on, with nary a thought to medical implications involving ingesting raw meat: Have you been to a Milwaukee wedding lately? Cannibal sandwiches is an appetizer featuring raw, lean ground beef served on cocktail bread.
Cannibal sandwiches have been a festive dish in German, Polish, and other ethnic communities in the Milwaukee area since the 19th century. They were also tied to foodborne outbreaks in Wisconsin in 1972, 1978, and 1994. You are more likely familiar with a similar version, steak tartare as the offending food. This has lean ground beef seasoned with salt and pepper on a rye cocktail bread with sliced raw onions on top. Consume at your own risk!
Common Questions about Parasites and Bacterial Infections
Environmental factors, such as the closeness of the water supply to the habitat of a certain animal species, especially beavers, predispose the area to infestation with Giardia.
In the spring of 1993, there was a widespread outbreak of acute watery diarrhea among the residents of Milwaukee caused by Cryptosporidium. It was estimated that 400,000 people had diarrhea, and there were 100 deaths in the elderly and other immune-compromised individuals.
There is a wide array of harmful bacteria that cause intestinal infection: Salmonella, Campylobacter, Shigella, and a special type of E. coli.