A randomized, controlled trial of the toxin-blocking effects of B subunit in family members of patients with cholera

A randomized, controlled field trial was performed to test the ability of B subunit, the nontoxic, binding portion of cholera toxin, to block the toxin receptors (G(M₁) ganglioside) in the small intestine and thereby prevent diarrhea in individuals infected with Vibrio cholerae O1. Of 1,922 family contacts of 370 index patients selected randomly to receive orally on two successive days either B subunit (low dose, 1.0 mg; high dose, 5.0 mg) or placebo, 190 were asymptomatically infected on day 1 or day 2 of the study and within 24 h ots receiving B subunit. During the first 24-hr period of follow-up, the relative risk of disease among contact receiving B subunit versus placebo was 0.18 for the low dose (P = .08) and 0.50 for the high dose (P = .22). Subsequently the relative risk increased toward 1.0 and was at no single point significantly reduced, although in five of the six follow-up periods the risk of disease was less in the B subunit group.