Oocysts of Cryptosporidium parvum, a zoonotic waterborne pathogen, can be r
emoved by bivalve molluscs from contaminated water and retained on gills an
d in hemolymph. We identified oocysts of C. parvum in oysters from seven si
tes in the Chesapeake Bay area. These findings document the presence of C.
parvum infectious for humans in oysters intended for human consumption.