New findings in the recent Salmonella Typhimurium contamination of peanut butter have authorities thinking that it has sickened more than 470 people and is implicated in as many as 6 deaths. Epidemiology is tricky, and according to the FDA's website, this outbreak may go as far back as five months.
"On January 16, [Peanut Corporation of America] expanded its voluntary recall to include all peanut butter produced on or after August 8, 2008, and all peanut paste produced on or after September 26, 2008, in its Blakely, Ga., plant because of potential Salmonella contamination. (via fda.gov)"
Here is a chart that shows the onset of this particular outbreak; it's called an epidemic curve, or "epi curve" for short.
They say that these epi curves are "complex and incomplete" but there are key five points to understanding them better:
- There is an inherent delay between the date that an illness starts, and the date that the case is reported to public health authorities. It typically takes 2-3 weeks for Salmonella infections.
- Some background cases of illness are likely to occur that would have occurred even without an outbreak. This makes it difficult to say exactly which case is the first in an outbreak. For some cases, the date when they became ill is not known because it takes time before someone from the health department can do an interview to ask for this information.
- It can be difficult to determine when cases start to decline because of the reporting delay.
- It can be difficult to say when the outbreak is over, [also] because of the reporting delay.