Dan McGee

1. An Outbreak of E. coli O157:H7 Infection Dan McGee

2. Surveillance CDC EIS

3. June 1997 Michigan Department of Community Health 52 laboratory reports of E. coli O157:H7 infection. 18 were reported in June of 1996. The increase in cases continued into July.

4. Artificial increase? • increased culturing of stools • initiation of new testing by the laboratory (i.e., lab did not undertake necessary procedures to isolate this organism in the past) • laboratory error in identification • contamination of cultures • changes in reporting procedures • errors in data entry

5. Real increase? • an increase in population size • changes in population characteristics (with an influx of persons at higher risk for the infection) • an increase in rate of infection due to random variation (fluctuation) in incidence (i.e., chance) • an increase in rate of infection due to an outbreak common source exposure increase in behaviors [e.g., outdoor cooking]

6. Case Resident of Michigan with onset of symptoms between June 15 and July 15 diarrhea (≥3 loose bowel movements a day) and/or abdominal cramps Stool culture yielding E. coli O157:H7 with the outbreak strain PFGE pattern.

7. 38 cases of E. coli O157:H7 infection meeting the investigation case definition were reported from 10 counties in the lower peninsula of Michigan

8. Typical incubation period for E. coli O157:H7 is 3-4 days – ranges from 3-8 days, Exposures in the 7 days before onset of illness considered. A complete food history in the last 7 days

9. Thirty-one Cases Two controls for each case. matched to the case by age and gender.

10. 15 (56%) of 27 ill persons reported eating alfalfa sprouts in the 7 days before onset of illness, Three (6%) of 53 controls reported eating them in the same 7 days No other food item was significantly associated with illness.