Press accounts, as well as those from the CDC, addressing the number of sick people in the ongoing Salmonella sprouts outbreak are a little misleading if you don’t know what is actually being said. The reality of these outbreaks (whether E. coli O157, Salmonella, or anything else) is that the number of people who are actually ill, as opposed to the number who have a stool sample that tests positive, is much bigger than the reports would indicate.
In fact, one of the leading studies on the subject suggests (and this is obviously not a bright line rule) that the number of actual victims in a given outbreak, as opposed to merely those with positive stool samples, is as much as 38 times the number of stool sample confirmed individuals. I hope that makes sense. Paul Mead et al, explain it much more clearly in their article, which I will post in a few minutes (technical difficulties).
So do the math in the ongoing Salmonella sprouts outbreak. Health officials report 31 confirmed illnesses. So 31 x 38 . . . . . equals 1,178!!!!!! But keep in mind that this is not the whole story. The ongoing outbreak in MI, MN, SD, UT, PA, WV is the same strain of Salmonella, Saintpaul, as the outbreak in NE, SD, MN, IA, and KA that sickened 121 people (stool sample confirmed). So again, doing the math and, admittedly, using the high end approach just to get a sense for the possible scope of these recent sprout outbreaks, that’s 121 x 38 . . . . 4,598!!!!!!
Now, it is only fair to add these two totals together (1,178 and 4,598), since the outbreaks are clearly linked, and likely by a common supplier of sprout seeds. Applying the math, the total number of ill people in these outbreaks could be 5,776. I am not saying that it is. In fact, it’s probably not that high. But the point is that there are many more sick people in these combined outbreaks than the numbers currently being reported would suggest.
Here are several reasons why, including a few excerpts from the Mead article:
First, and perhaps most importantly, it is highly unlikely that, from a batch(es) of hundreds of thousands (maybe millions???) of sprouts seeds, only the seeds that the stool sample positive people eventually consumed were contaminated with Salmonella Saintpaul. More likely is that many of the seeds were contaminated, leading to a proliferation of the Salmonella bacteria during the growth, cultivation, and harvest phase.
Second, as noted by Mead et al., underreporting of foodborne disease is common. See Mead Article at 607. “Surveillance of foodborne illness is complicated by several factors. The first is underreporting. Although foodborne illnesses can be severe or even fatal, milder cases are often not detected through routine surveillance.” It is frequently the case that only the more severe illnesses come to the attention of health department officials. The less severe illnesses in any given outbreak often require less medical treatment, and the possibility that the causative agent—e.g. Salmonella bacteria—will be identified decreases as well.
Many cases of foodborne illness are not reported because the ill person does not seek medical care, the health-care provider does not obtain a specimen for diagnosis, the laboratory does not perform the necessary diagnostic test, or the illness or laboratory findings are not communicated to public health officials.
See Mead Article at 609.
Finally, the likelihood that secondary transmission of Salmonella-bacteria occurred must be considered. As stated in the Mead Article, “many pathogens transmitted through food are also spread through water or from person to person, thus obscuring the role of foodborne transmission.” See Mead Article at 607. In other words, it is common in outbreak situations for people who became infected by contaminated food to thereafter sicken co-workers or family members by unwitting transmission of a small amount of bacteria.
These circumstances constellate, in my view, to make it highly likely that the sprouts outbreak was much larger than (121 plus 31) 152 sick people. As Mead states:
To calculate the total number of illnesses caused by each pathogen, it is necessary to account for underreporting, i.e., the difference between the number of reported cases and the number of cases that actually occur in the community. For Salmonella, a pathogen that typically causes nonbloody diarrhea, the degree of underreporting has been estimated at ~38 fold . . . [W]e used a factor of 38 for pathogens that cause primarily nonbloody diarrhea (e.g. Salmonella, Campylobacter).
See Mead Article at 607.
Food for thought anyways.