Infant: E. coli (enteropathogenic), rotavirus.
Child/adult without travel, afebrile, diarrhea with no gross blood or WBCs in stool: Rotavirus, norovirus and other caliciviruses, E. coli (GNR).
Child/adult with acute watery diarrhea, low-grade fever: E. coli (GNR) (enterotoxigenic (ETEC), enteroinvasive (EIEC), Clostridium difficile (GPR), norovirus.
Child/adult with fever and dysentery (WBC in stool): E. coli (EIEC), shigella (GNR), Campylobacter sp. (GNR).
Child/Adult with diarrhea, bloody stool or history of travel to subtropics/tropics (or elsewhere) (varies with epidemiology): E. coli (GNR), enterohemorrhagic (EHEC, 0157:H7, STEC O104:H4), and other shiga-toxin-producing E. coli serotypes).
Other causes of acute diarrhea: salmonella (GNR), Yersinia enterocolitica (GNR), aeromonas (GNR), plesiomonas (GNR), vibrio (GNR), cryptosporidium, Entamoeba histolytica, Giardia lamblia, cyclospora, strongyloides, microsporidia (in HIV infection).
Child/adult with diarrhea and vomiting: E. coli (EPEC, enteropathogenic), norovirus.
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