• Salmonella enteritidis bacteria: In the United States, these bacteria (found in contaminated raw or undercooked chicken and eggs) are a major cause of food poisoning, especially during summer.
• Campylobacter bacteria: Infants and young adults are most commonly affected by these infections, especially during the summer. The bacteria are often found in raw and undercooked chicken.
• Shigella bacteria: Shigella infection (called shigellosis) spreads easily in families, hospitals, and child-care centers. Kids 2 to 4 years old are the most likely to be infected.
• Giardia parasite: Infection with Giardia (called giardiasis) is easily spread through child-care settings and contaminated water supplies, especially water parks and pools (the bacteria are resistant to chlorine treatment), children's "touch tanks" in aquariums and museums, and contaminated streams or lakes.
• Cryptosporidium parasite: Found especially in drinking and recreational water, this parasite often is the culprit behind diarrhea epidemics in child-care centers and other public places. Cryptosporidiosis often causes watery diarrhea that can last for 2 weeks or more.