VALIDATION OF A VOLUNTEER MODEL OF CHOLERA WITH FROZEN BACTERIA AS THE CHALLENGE

To evaluate a standardized inoculum of Vibrio cholerae for volunteer c hallenge studies, 40 healthy adult volunteers were challenged at three different institutions with a standard inoculum prepared directly fro m dials of frozen, virulent, Fl Tor Inaba V. cholerae N16961, with no further incubation. Groups of 5 volunteers, with each group including 2 volunteers with blood group O, were given a dose of 10(5) CFU, and 3 4 of the 40 volunteers developed diarrhea (mean incubation time, 28 h) , Transient fevers occurred in 15 (37.5%) of the volunteers. V. choler ae was excreted by 36 of 40 volunteers. Five additional volunteers rec eived 10(4) CFU, and four developed diarrhea but with a lower average purging rate than required for the model. Of the 40 volunteers, 37 dev eloped rises in their vibriocidal and antitoxin titers similar to thos e in previous groups challenged with freshly harvested bacteria, We co nclude that challenge with frozen bacteria results in a reproducible i llness similar to that induced by freshly harvested bacteria. Use of t his model should minimize differences in attack rates or severity when groups are challenged at different times and in different institution s.