Infectious diarrhea. Managing a misery that is still worldwide. Infectious diarrhea is the largest single cause of morbidity and mortality in the world. Bacteria, viruses, and protozoan parasites are the most common causative agents. Treatment in most cases of bacterial and viral diseases consists of correcting fluid loss and electrolyte imbalance by oral or parenteral rehydration. Antimicrobial therapy is reserved for very ill patients only. With the exception of Cryptosporidium, for which no effective agent is yet available, all protozoan infections are treatable with metronidazole. 