It’s a week since an alarming nationwide outbreak of food-related e.coli was first identified, with 113 confirmed cases of the shigatoxigenic (or STEC) variant hospitalising at least 37 people. And as I write this, still the source is unidentified.

It’s an extraordinary situation, when you consider the levels of provenance-based intelligence to which food retailers have access. But e.coli is a slippery bacteria and increasingly so.

Historically, the most common cause of e.coli was poorly prepared or undercooked meat. The esteemed bacteriologist Hugh Pennington speculated this week it was likely a dairy item, another common culprit. But a source close to the investigation told The Grocer this week the outbreak was more likely fresh produce, potentially via sandwiches or salads. And that’s way more tricky from a consumer safety point of view: while the FSA reiterated its advice this week to always wash fruit & veg before consumption, you cannot easily wash an e.coli-infested sandwich or prepared salad.

In fresh produce, the culprit is invariably a contaminated water supply. In one outbreak it was even found in walnuts. And the investigation is further complicated by likely involving a multi-component item.

The tragic STEC outbreak in Germany a few years back was ultimately linked to infected beansprouts, but not before cucumbers were wrongly fingered – resulting in huge losses for innocent Spanish cucumber growers. So regulators cannot apportion blame without firm evidence.

A further problem is that while whole genome sequencing enables regulators to link the cases, some stem back several weeks. Asking patients to remember what they ate grows harder with every passing day.

And finally, as we explain in this issue, for worried manufacturers and producers, the testing regimes are both hugely expensive and notoriously unreliable. The good news is, it’s 100 people getting sick, not 1,000 or 10,000, and no one has died. Let’s hope that remains the case, while they track down the cause.