A diarrheal illness occurs when normal host defenses are overwhelmed by microbial virulence. There are other causes of diarrhea as well. Microorganisms can cause this if they produce infection-causing toxins. Bacteria can generate enterotoxins which can lead to copious, typical diarrhea by acting on the secretory mechanisms directly. When bacteria produce cytotoxin, it causes bloody stools containing inflammatory cells due to mucosal cell destruction. This results in a reduction in absorptive ability. Other causes include enterocyte invasion, achlorhydric states, hypomotility states, the ingestion of toxins and pathogenic organisms, norovirus, and normal bowel flora alteration (typically occurs after antibiotic administration).