The E. coli O145 outbreak in Michigan, Ohio, and New York, which has long had a suspected lettuce link (and was publicly confirmed today), has no doubt sickened quite a few people.  Just how many, however, is hard to know for sure.  Some reports put the number as high as 60.  Some say 47.  Today, the FDA stated that there are 19 confirmed illnesses with ten more pending.  Of the 19 confirmed illnesses, according to the FDA, 12 people were hospitalized and 3 developed hemolytic uremic syndrome (HUS). 

The true scope of this outbreak, one of many in a long line of lettuce and leafy green e. coli outbreaks, will probably not be known for some time.  One thing is for sure, however, about the number of people already affected by it.  It is a bigger number than 19 (because the FDA/CDC will only count people who have a culture confirmed infection that is a genetic match to the outbreak strain); it is a bigger number than 29 (the number of confirmed illnesses, plus those that are pending); and its probably bigger than any other estimates to date as well.  

Illnesses in foodpoisoning outbreaks are notoriously underreported.  In fact, that is one problem that epidemiologists face in nearly any outbreak of foodborne disease (whether e. coli, salmonella, hepatitis, campylobacter, or anything else), and it sometimes frustrates their attempts to identify the actual cause of an outbreak.   

There are any number of reasons why foodpoisoning cases go unreported, thus depriving investigating health authorities of the benefit of knowing what the ill person ate.  The person did not see a doctor, or a stool sample was not done, or the sample returned a false negative result, or the person took antibiotics before submitting the sample. 

But another reason why this particular outbreak may have caused many more illnesses than the numbers that are currently being stated is that the outbreak strain, E. coli O145, is frequently not tested for.  Thus, even if an ill, infected person does have a stool sample tested, the sample may not return a positive result. 

Discussing just this issue, the Center for Infectious Disease Reporting and Policy at the University of Minnesota (CIDRAP) issued a detailed statement today on the E. coli O145 lettuce outbreak linked to contaminated Freshway lettuce:

The CDC said there are limited surveillance data on illnesses involving non-O157 serotypes of Shiga toxin-producing E coli (STEC), including O145. "Therefore E coli O145 may go unreported. Because it is more difficult to identify than E. coli O157, many clinical laboratories do not test for non-O157 STEC infection," it said in the press release.

Craig Hedberg, PhD, a food safety expert at the University of Minnesota in Minneapolis, told CIDRAP News that the outbreak is similar to E coli O157:H7 outbreaks that have previously been linked to lettuce. E coli O145 has been associated with cattle, like O157 and other STEC strains. "And it seems likely that cattle would have been the reservoir source of contamination for this outbreak as well," he said. "Of course, since the production source has not been identified, this is all speculation on my part, but it seems likely."

One of the leading studies on the subject of underreporting suggests  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.  If there are 29 confirmed (or pending confirmation) illnesses in this outbreak, the number of people actually sickened may be . . . a little scary.  Time will tell.