Relating Numbers of Foodborne Pathogens to Human Illness: Question and Answer Sessions - David Tribble, MD
Food Safety Initiative Technical Workshop:
Relating Numbers of Foodborne Pathogens to Human Illness
Introduction | Program | Talks | Abstracts | Qs & As | Slides | Biographies
Tuesday, August
4, 1998
Atrium, Stamp
Student Union
University
of Maryland
College Park,
MD
Question and Answer Sessions
David Tribble, MD
QUESTIONER: [Inaudible.] What kind of factors determine dose selection?
DR. TRIBBLE: I'll try to repeat. Let me just make sure I have the correct question. Your question was what were we using in our study to determine the dose selection in the Campylobacter study?
We primarily used the pre-existing information from the CVD study. In this study there was a lack of a illness dose-response at doses up to 109 inoculum in the same strain that we were using. The CVD investigators observed around 40 to 50 percent overall attack rate for diarrhea or fever.
That was the reason we chose as high a dose as 109 as one of the initial doses. The reason we chose the 105 dose as our lowest dose was based partly on the results from the C. jejuni A3249 strain. With this strain, a 46% attack rate was demonstrated in the 104 dose however, the attack rates were very inconsistent across the dose range. Using the bicarbonate buffer delivery modification, it was conceivable that a more consistent attack rate could be demonstrated at this lower dose. Another modification from the CVD study was the use of screening Campylobacter serology with enrollment of only seronegative volunteers. In the CVD study, retrospective analysis of baseline serology detected a decreased risk of illness post-inoculation in volunteers with elevated baseline serology. So those were the reasons we used that range. Limited number of inpatient beds, ward time availability, and limited number of volunteers were also considerations. Logistical concerns do weigh heavily in the design of these trials.
