Please read the background reading attached. Please answer question below after reading. What are the advantages and disadvantages of the case definition? Describe and compare the age and gender distribution of E. coli O157:H7 cases from this outbreak and those reported from U.S. FoodNet sites in 1997. What kinds of questions would you ask in the hypothesis-generating interviews? 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 incubation period for E. coli O157:H7 ranges from 3-8 days with a median of 3-4 days. The infection often causes severe bloody diarrhea and abdominal cramps, but can also cause a nonbloody diarrhea or result in no symptoms. In some persons, particularly children under 5 years of age and the elderly, the infection can cause a complication called hemolytic uremic syndrome, in which the red blood cells are destroyed and the kidneys fail. About 2-7% of infections lead to this complication.
For this outbreak investigation, a case was defined as diarrhea (at least 3 loose bowel movements a day) and/or abdominal cramps in a resident of the state with onset of symptoms between June 15 and July 15 and a stool culture yielding E.coli O157:H7 with the outbreak strain PFGE pattern.
Of the initial 38 persons who met the case definition, 26 (68%) were female with amedian age of 31 years. (Table 1)
Table1. Age group and gender distribution for persons with E. coli O157:H7 infection and the outbreak PFGE pattern, June 15 - July 15, 1997. (N=38)
The 38 cases of E. coli O157:H7 infection meeting the investigation case definition were reported from 10 counties. On set of illness occurred from mid-June to mid-July, peaking on June 22.
From July 16 - 19, hypothesis-generating interviews were undertaken with seven patients. These patients lived in four different counties and ranged in age from 5-69 years. Three of the patients were female.
Hypothesis-generating interviews revealed that most cases had consumed lettuce and alfalfa sprouts in the week before they became ill. No single restaurant or social event was identified in common.
APPENDIX 1. Distribution of E. coli O 157:H7 cases reported to FoodNetSites* by age group and gender, United States, 1997. (N=340)
Case definition can also be disadvantageous because there is a possibility that patients exhibiting same symptoms as may be wrongly diagnosed. This could be hazardous because a patient may be treated with medication for E. Coli when they are in fact suffering from another ailment.