The first source of information for hypothesis generation in any outbreak is case-patients group which will provide valuable information on the "potential sources of exposure" (Meijia, 2006). In case the case-patient is unavailable, family member or friend must be interviewed. In case, the case-patient is a child, or guardian must be interviewed. Based on the size of the outbreak, about 8-10 cases of different demographic characteristics must be selected for the interview. Preferred are those cases which have occurred during the middle of the outbreak and those with typical case presentations. However, it is important to remember that even unusual cases may provide important clues. The following questions may be asked (Meijia, 2006):
4. Given your knowledge about E. coli O157:H7, the descriptive epidemiology of the initial cases, and the results of hypothesis-generating interviews, outline the information available at this point on the source of the outbreak and mode of transmission.
The source of outbreak has been attributed to alfalfa sprouts and lettuce. Thus the possible sources of contamination are deer feces, cattle manure and irrigation water. The mode of transmission is