Colibacillosis is a common systemic disease of economic importance in poultry and occurs worldwide. Escherichia coli infection occurs as an acute fatal septicemia or subacute pericarditis and airsacculitis, as well as perihepatitis, arthritis, and also cellulitis. Among bacterial infections, colibacillosis is very often the first cause of morbidity and mortality in poultry. Large numbers of E. coli are maintained in the poultry house environment through fecal contamination. Systemic infection occurs when large numbers of pathogenic E. coli gain access to the bloodstream via the respiratory tract or intestine. Bacteremia progresses to septicemia and death, or the infection extends to serosal surfaces, pericardium, joints and other organs. Uncontrolled, avian E. coli represents a serious animal welfare concern and risk to public health as it is a zoonotic organism with avian E. coli species known to adapt to humans.