By: Heather Williams

What seemed like an outbreak of E. coli in Canada seems to be reaching farther than initial reports.  Starting in early December, the Public Health Agency of Canada identified an outbreak with symptoms originating as early as November 2017.  On the last report on the Public Health Notice from the Public Health Agency of Canada on December 28, 2017, the illnesses are up to 41 cases, including 17 hospitalizations, and 1 death and spanning 5 of Canada’s Eastern provinces.  As at least one new case was added on that report, and authorities believe the outbreak is not over and the still unknown source is still causing illness.  Based on patient interviews, the Canadian health agency believes that the outbreak is linked to romaine lettuce.  Most of those who were interviewed reported that they consumed romaine lettuce prior to becoming ill with this diarrheal illness.  Unfortunately, despite the Canadian Food Inspection Agency testing several romaine lettuce sources for E. coli contamination, no source has been identified.

On the same day as the Canadian report, the United States’ Centers for Disease Control and Prevention (CDC) issued a Media Release disclosing an E. coli outbreak that has linked 17 illnesses across 13 states.  The CDC implies that this outbreak also appears linked to E. coli and that while whole genome sequencing is necessary to be certain, the two outbreaks of E. coli seem to have genetic similarities.  This provides a strong tentative suggestion that the two outbreaks are actually one outbreak that crosses country boarders. Could Canada’s outbreak be the same outbreak as the United States’ outbreak?

Based on the growing seasons of romaine lettuce, it seems that the tainted romaine likely originated in the United States or possibly Mexico – as these regions are in season for romaine during the illness onset period.  This should make it easy to identify the source, prompt a recall, and stop the outbreak from spreading.  Right???  Well, it isn’t as easy as it sounds.  So much goes into the process of linking each new case to the outbreak and then linking a source to the outbreak.  Investigators have their hands full with the abundance of information to sort through.  But what exactly would it take to figure out where the source of the contamination began and how it hopped boarders before returning to the United States.  That is, if it truly originated in an American farm.

How Cases are Linked Together

So many outbreak illnesses can be resolved with over the counter symptom treatment and normally healthy individuals often recover without any medical care.  Unfortunately, those cases do not get linked to the outbreak.  The ones that start to get epidemiologist attention are those that seek medical treatment and have their samples tested.  When more than two individuals report the same illness, flags start being raised.  Samples such as those to diagnose E. coli illness are usually analyzed to identify the responsible strain.  When other unrelated individuals also turn up positive for that same strain, the cases are then linked, and investigators approach them as part of an outbreak.  Additional testing can be performed to provide more information about the specific strain of bacteria responsible for the illness.  In the case for the Canadian E. coli outbreak and the United States E. coli outbreak, not only were the individual cases linked, but it appears each country’s outbreak is also linked.  Though whole genome sequencing must be completed to confirm this phenomenon.  Once the cases are linked, further investigation ensues to determine the source of the outbreak.

How a Source is Identified

Initially patents are tested with rule-out panels to identify the type of illness.  Additional genetic testing allows the cases to be confirmed and officially linked.  Patient interviews are investigators’ next step in identifying the source of the outbreak.  Patients are asked where they have been, what they have eaten, and any other information that could link the patients’ activities to a source.  This information is reconciled to determine what foods and/or activities overlap the cases.  At this point, investigators can start testing samples to determine the source of the outbreak, initiate a recall, and hopefully stop the spread of the outbreak.

In the E. coli outbreak spanning the United States and Canada, patient interviews indicated that many had consumed romaine lettuce prior to becoming ill.  Romaine lettuce is a known source for E. coli outbreaks in the past, and when many report consuming this produce item it is a good place to start.  Armed with the genomic information from whole genome sequencing, investigators can track down the specific brands and hopefully lots of the potential food source and test it for E. coli.  If the genomic sequencing matches, the source has been identified.

In this case, the fact that the cases span international boarders should narrow potential distributors and then link back to farms.  Investigators’ next steps should be identifying which distribution networks overlap the two countries.  This should narrow the proverbial ‘needle in a haystack’ to a bowling pin in a pile of hay.  Unless the contaminated product has already been distributed and no other contaminated product is available for consumption, it should be readily tracked down and identified with whole genomic testing.  This is the part that takes a little bit of time.  Once the source is identified, what happens from there?

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What Happens from There?

Imagine that the source is identified next week.  It turns out that ABC distributor has a network that reaches both the United States and Canada.  A shipment to each country screens positive for E. coli and further whole genomic analysis indicates the strain matches the E. coli that infected patients from both countries.  Now ABC distributor can assist the investigation, disclosing the farms and process by which the produce is handled by the distributor.  Let’s say that ABC distributor has on record sending product from XYZ farm to both countries.  Investigators might visit that farm or set of farms indicated the likely source and analyze samples in the same manner as performed on the distributors products.  At this point the source is known and a more specific recall should be prompted.  If all goes well, the farm and distributor cooperate and issue a voluntary recall, otherwise governmental authorities may have to intervene. Generally, farms and companies want to do the right thing.

Source for Current Outbreak(s)

At this time fingers are only cautiously being pointed to romaine lettuce, though the final stages of sample identification are near.  If all goes well, the contaminated product can be identified, and the outbreak can stop at the current number of illnesses.

UnsafeFoods will continue to monitor the situation as more information becomes available.