Many strains of diarrheagenic E. coli primarily affect popula-tions in developing countries. There is a wide variation in the prevalence of these strains worldwide. EPEC, EAEC, and DAEC have been reported to occur most often in developing coun-tries. ETEC is the primary cause of traveler’s diarrhea and is the major cause of infantile diarrhea in poor and developing countries. ETEC causes nearly more than 600 million cases of diarrhea every year and 700,000 deaths in children below 5 years. EHEC is an emerging cause of food-borne disease, particularly in the northern United States and Canada. Outbreaks of HUS in children that caused fatalities have also been documented in these countries.
Most strains of E. coli causing diseases in humans inhabit the human intestine. Few strains, such as EHEC, inhabit the cattle intestine also.
Most E. coli infections with the exception of neonatal men-ingitis and gastroenteritis are endogenous. The infection is caused by theE. coli that constitute the patient’s normal micro-bial flora. These bacteria cause infections, such as UTI, due to poor personal hygiene or when the patient’s defenses are compromised. Diarrhea caused by E. coli is widespread in areas with poor sanitation, and infections are exogenous. Food and water contaminated with human or cattle feces are important sources of diarrheagenic E. coli. Ground beef, apple juice, and alfalfa sprouts contaminated with cattle feces are important sources of infection caused by enterohemorrhagic E. coli(e.g., O157:H7). Infection is acquired by ingestion of contaminated food or water. The usual source of E. coli in neonatal infections is the intestinal tract of the mother. The bacteria may also be acquired nosocomially, particularly in infants who are prema-ture or who require mechanical ventilation. Humans and also cattle (for E. coli O157:H7) are reservoirs of infection.