Outbreak fading fast - Date of onset

From the CDC:

The outbreak can be visually described with a chart showing the number of persons who became ill each day. This chart is called an epidemic curve or epi curve. The epi curve and information about interpreting it may be found here. It shows that the number of persons who became ill peaked during May and decreased in June. The average number of persons who became ill between May 20 and June 10 was 33 per day. The average number of persons who became ill between June 11 and June 20 was 19 per day. Illnesses that occurred after June 20 may not yet be reported due to the time it takes between when a person becomes ill and when the illness is reported. This takes an average of 2-3 weeks. The outbreak appears to be ongoing, but with fewer new illnesses each day. Please see the Salmonella Outbreak Investigations: Timeline for Reporting Cases for more details.

TK: What does this information mean? From the Food Safe Group, Robert LaBudde said this:


CDC has given the outbreak curve, which now allows some conclusions to be reached:
http://www.cdc.gov/salmonella/saintpaul/epidemic_curve.html
1. Cause of the outbreak stopped feeding into the distribution system around the end of May. The growth was exponential from April through May, which suggests much more than simple contamination of a few lots. Some type of feed back may have been present.
2. Cases since then are due to capacitance of the distribution system, and discharging this capacitance is still underway, but is nearly over.
Because the source and amplification of the outbreak was disconnected at the end of May, any investigations (e.g., sample and test) by CDC and FDA after that point would be fruitless.
However, there would have been a useful purpose in examining product already in distribution (e.g., warehouses, storage at restaurants, etc.)
It would be interesting to know what happened at the end of May to terminate the propagation mechanism. Presumably it had something to do with the CDC investigation and fixation on tomatoes.
So CDC appears to have done the job, even if it did so in partial ignorance.
Of course, we may never know how the outbreak came about in the first place, as the trail is now cold.

================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: r...@lcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947