How We Actually Monitor an Outbreak

A CDC website lays out how we actually identify an outbreak of O157:H7. Guess what? It doesn’t happen like it does in the movies or on TV. This is why keeping these networks fully functional (i.e., adequately funded) matters: time is critical and delays in processing due to inadequate resources or personnel can be deadly. For kicks, imagine if this were something far more contagious than a food-borne pathogen.
Here’s the timeline:

1. Incubation time: The time from eating the contaminated food to the beginning of symptoms. For E. coli O157, this is typically 3-4 days.
2. Time to treatment: The time from the first symptom until the person seeks medical care, when a diarrhea sample is collected for laboratory testing. This time lag may be 1-5 days.
3. Time to diagnosis: The time from when a person gives a sample to when E. coli O157 is obtained from it in a laboratory. This may be 1-3 days from the time the sample is received in the laboratory.
4. Sample shipping time: The time required to ship the E. coli O157 bacteria from the laboratory to the state public health authorities that will perform “DNA fingerprinting”. This may take 0-7 days depending on transportation arrangements within a state and the distance between the clinical laboratory and public health department.
5. Time to “DNA fingerprinting”: The time required for the state public health authorities to perform “DNA fingerprinting” on the E. coli O157 and compare it with the outbreak pattern. Ideally this can be accomplished in 1 day. However, many public health laboratories have limited staff and space, and experience multiple emergencies at the same time. Thus, the process may take 1-4 days.

The time from the beginning of the patient’s illness to the confirmation that he or she was part of an outbreak is typically about 2-3 weeks. The average for cases in this outbreak so far has been 15 days. Case counts in the midst of an outbreak investigation must be interpreted within this context.

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