After flooding the gravest concern is contaminated drinking water so any pathogen spread by water is a concern. These pathogens include Vibrio cholerae, enterotoxigenic E. coli, Shigella, Salmonella enterica (serovar Typhi), norovirus, hepatitis E, Giardia, and Cryptosporidium.
Enterohemorrhagic E. coli produce the Shiga toxin, which causes capillary thrombosis and blood in the stool. They also cause effacement of the intestinal microvilli. Enterohemorrhagic strains attack the colon by adhering through attachment proteins and using the secretion injection system to deliver proteins into the target cells. The proteins then radically alter the cytoskeletal components of the cells. Attachment and effacement causes the diarrhea, while the Shiga toxin produces capillary thrombosis and inflammation of the colonic mucosa, leading to hemorrhagic colitis. The Shiga toxin can also circulate in the blood and bind to renal tissue, causing glomerular swelling and the deposition of fibrin and platelets in the blood vessels.
Attachment of adult worms to the colonic mucosa produces haemorrhaging and localized ulcerations that can be used as portals of entry for opportunistic bacterial infections. Consequently, concomitant bacteraemia can often be seen with this parasitic infection. Although light infections are usually asymptomatic, with more moderate worm loads there can be damage to the intestinal mucosa, accompanied by nausea, diarrhea, and abdominal pain. Some children can have worm loads as high as 800, and in these cases there is significant mucosal damage, blood loss, and anemia. When these children strain to defecate, the sheer force of the fecal stream on the worm bodies can cause prolapse of the colonic or rectal mucosa out through the anus.