TABLE 3.2.

Outbreaks of Diarrhea by Organism

Organism	Inoculum Required to Cause Diarrhea in Adult Volunteers	Attack Rate in Enrollees (%)	Secondary Attack Rate in Family Members (%)	Asymptomatic Excretion in Enrollees
Rotavirus	18–1000 virions	50	15–80	Common

Enteric adenovirus	Unknown	40	Unknown	Common

Astrovirus	Unknown	50–90	Unknown	Common

Calicivirus	Unknown	50	Unknown	Common

*Giardia intestinalis*	10^1-2 cysts	17–54	15–50	Common

*Cryptosporidium*	132 oocysts	33–74	25–60	Common

*Shigella*	10^1-2	33–73	25–50	Uncommon

*Escherichia coli*	10⁸
O157:H7		29, 34	Unknown	Uncommon
O114:NM		67	Unknown	Uncommon
O111:K58		56, 94	Unknown	Uncommon

*Clostridium difficile*	Unknown	32	Unknown	Common