Enterotoxigenic E. coli also is commonly associated with traveler's diarrhea. Prophylaxis against this infection may be achieved by providing passive immunity with immune milk. A bovine whey protein concentrate from cows immunized with enterotoxigenic E. coli serotypes and consumed 3-times daily for seven days protected all of the adult volunteers from developing diarrhea after being challenged with an enterotoxigenic E. coli strain [64] . In contrast, 90% of the volunteers who received control immunoglobulin concentrate prior to challenge developed diarrhea after the E. coli challenge. Subsequent studies using IgG isolated from bovine colostrum from cows hyperimmunized against specific E. coli colonization factor antigens also have shown protective effects in volunteers challenged with colonization factor antigen-bearing enterotoxigenic E. coli [65] , however other studies by the same group did not demonstrate significant effects of similar milk immunoglobulin products [66] .