Experimental Human Salmonellosis

Summary Immunity after experimental human infections due to Salmonella meleagridis and S. ana um was studied by challenging the subjects at various intervals and dose levels. Some increased resistance was found in all twenty-three subjects studied although the degree varied considerably. On the first refeeding using somewhat larger doses of the same strains, sixteen of the twenty-three subjects did not become ill. Of seventeen subjects refed a second time using considerably larger doses, seven again did not become ill. The great majority of illnesses produced by first or second refeeding were milder than the initial illnesses. An increased resistance was present in some instances as long as nine months after the initial attack. Seven men who developed prolonged carrier states in the initial experiments, with one exception, ceased excreting the organism promptly in the refeeding experiments.