Multi-state E.coli Outbreak.
A person having diarrhea with loose stools greater than 3 bowel movements in a day with or without abdominal cramps, who is a resident of Michigan, having onset of symptoms between the 15th of June and 15th of July and the stool cultures yielding E.coli 157:H7. (Lautenbach, E., 2008). (Multistate Outbreak of E.coli O157:H7 Infection, 2008)
It is an infection leading to severe abdominal cramps and bloody diarrhea. Non bloody diarrhea can also occur, or it may also be that the patient will have no symptomatic complaints. The causative organism is E.coli O157:H7 which has an incubation period of 3 to 8 days with a median of 3-4 days. (Lautenbach, E. 2008). . In people in extremes of age groups I.e. elderly and children under 5 years of age, the infection can also lead to complications like Hemolytic uremic syndrome.
By including a lab test as criteria for case confirmation, the specificity of the case definition increases hence the power of the test increases and so do the chances to detect the source.
Investigation: by making lab investigations like stool cultures and PFGE a criterion, people who had the symptoms but were not able to visit the doctor were not counted as having the disease, hence the sensitivity of the definition decreased.
By only taking residents of Michigan into consideration, people who were visitors and might have got infected were excluded from the count.
Slight alterations could be made to the case definition.
Proposed Case Definition
A person having diarrhea with loose stools greater than 3 bowel movements in a day with or without abdominal cramps. The person may be a resident or may have visited Michigan a week prior to having onset of symptoms between the 15th of June and 15th of July. A person with clinically compatible picture who is epidemiologically linked with a confirmed case of E.coli infection. The stool cultures yielding E.coli 157:H7.
The lab testing requirement still has to remains, to ensure specificity and power of the definition.
Comparison between age groups:
In the Michigan outbreak, it was noted that more than twice as many females were infected as were males. People in age groups of 20-39 and 40-59 were reported most frequent cases in the Michigan outbreak. Food net on the other hand reported nation wide distribution of cases almost equally in males and females, i.e. 162 to 178 respectively. They also documented that largest segmented of population infected in 1997 was in the age group of 1-9 years.
This pattern shows that in the Michigan outbreak, the source most probably started with some sort of interaction between source and the adult females of age between 20-59years.
Inquiry about disease
E.coli infection is mainly an oral-fecal transmission pathway. Hence poorly chlorinated water, unpasteurized milk are common fluid sources. Uncooked or improperly cooked beef another forms of meat are another likely source of transmission. Vegetables directly from farms or stores, which are not properly washed, like lettuce, spinach alfalfa etc are another source of infection. (Escherichia coli O157:H7, 2005). E
xposure to farm animals, or contact with infected people are also risk factors. In the United States infected children in daycare centers also a major source of spread. So questions pertaining to contact and handling of the above stated risk factors should be asked.
Source of the outbreak according to the currently present evidence is alfalfa sprouts. Contaminated alfalfa seeds initially caused the outbreak and then the infection easily spread through person to person transfer. The leading hypothesis is that contaminated alfalfa sprouts or seeds of alfalfa sprouts were the initial cause of the outbreak.
People who consumed these foods in the area of Michigan got infected with E.coli O157:H7 and then the infection were further transferred to other people with whom they came into contact.
Escherichia coli O157:H7 (2005). Division of Bacterial and Mycotic Diseases, Center for Disease Control and Prevention. Retrieved March 6, 2008, from http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_t.htm
Lautenbach, E. (2008). Outbreak Investigation: Discussion Group. Pennsylvania department of health. Retrieved March 6, 2008, from http://www.dsf.health.state.pa.us/health/lib/health/Outbreak_Investigation.ppt.
Multistate Outbreak of E.coli O157:H7 Infection, (2008). Foodsafety.net Retrieved March 6, 2008, from http://www.foodsafetynet.info/NEHA/EpiSlides/Ecoli_122803.ppt.