If a stool culture is positive for pathogenic bacteria, then they are the most likely cause of the person's diarrhea and other symptoms. Results are frequently reported out with the name of the pathogenic bacteria that was detected. Some of the most common pathogenic bacteria that cause infections in the U.S. and their most frequently encountered sources include: Campylobacter – found in raw or undercooked poultry and unpasteurized milk; it is one of the most common causes of bacterial diarrhea in the U.S. It may become especially serious if it spreads to the blood, and it occasionally causes long-term complications such as arthritis and Guillain-Barré syndrome. Salmonella – found in raw eggs (even intact disinfected eggs), raw poultry, uncooked vegetables, and in reptiles; pets such as lizards and turtles may carry salmonella in their intestines without being ill themselves. Some humans may become carriers of salmonella. Salmonella may be transmitted person-to-person. Shigella – found in food and water contaminated with stool and from infected person-to-person when careful sanitation is not observed; for instance, it can be a challenge to prevent the spread of Shigella within a family and in a daycare or nursing home setting since very few organisms may cause disease. A wide variety of other bacteria may sometimes cause GI infections and may be identified with a stool culture. Some important examples include: Escherichia coli 0157:H7 and other toxin-producing E. coli (most strains of E. coli are considered normal flora and do not cause disease) – found in raw or undercooked hamburger/beef, spinach, or unpasteurized cider; causes bloody diarrhea and may lead to hemolytic uremic syndrome. Clostridium difficile – may be present as part of the normal flora, but use of broad-spectrum antibiotics can result in an overgrowth of these bacteria. Toxin-producing strains can cause diarrhea and other serious complications. If these strains are suspected to be the cause, then separate tests that detect the toxin-producing C. difficile will be performed. Examples of other less common causes include: Aeromonas Plesiomonas Yersinia enterocolitica Vibrio cholerae and other Vibrio species For more on bacteria that cause GI infections, see the articles on Diarrhea, Food and Waterborne Illness, and Travelers' Diseases. Results of stool cultures that are reported as negative usually reflect the fact that the stool culture was checked for the most common pathogens at several intervals and none were found (not isolated). A report may state: "no Campylobacter isolated," "no Salmonella or Shigella isolated," etc. If the culture is negative for the major pathogens, then it is likely that the person's signs and symptoms are due to another cause or to a less common pathogen. It is also possible that pathogenic bacteria are present in the gastrointestinal tract, but there were too few bacteria in that particular stool sample to be detected. If a healthcare practitioner suspects that this is the case and symptoms continue, a stool culture on another sample may be ordered and/or followed up with other tests. Most diarrheal disease is caused by a single pathogen, but it is possible to have an infection with more than one.