Escherichia coli – E. coli for short – is a bacterium with two faces. Some strains produce toxins that cause gastrointestinal disease. Set these aside. We’re concerned with the other strains that live innocuously in the colon. They’re among the most abundant gut bacteria and only cause trouble if they reach other body sites.
This happens if the gut contents leak during surgery, for example, or via a ruptured appendix. More commonly, particularly in women, gut E. coli reach the urinary tract and swim upwards, causing UTIs (urinary tract infections). Some strains are especially adept swimmers; five or six ‘uropathogenic’ lineages account for half of all UTIs.
In total, E. coli causes 80% of all UTIs, with 150 million cases annually worldwide. Most are painful but self-limiting ‘cystitis’, reaching no higher than the bladder. These used to be treated with trimethoprim. Nowadays, owing to trimethoprim resistance, nitrofurantoin is preferred. A few reach the kidneys and, worse, then spill into the bloodstream. That’s bacteraemia – bacteria in the blood – which can trigger life-threatening sepsis.
E. coli accounted for a third of all U.K. bacteraemias in fiscal year 2019-20, with a tally of 43,395 cases, mostly in the elderly. Hospitals in England are obliged to report these, so numbers should be robust. UTI ‘overspill’ accounts for at least half; gut leakage for a quarter. Most UTI-origin cases develop in the community and enter hospital through A&E.
Around 18% of E. coli bacteraemia patients die in the U.K. This rate roughly doubles if treatment is inadequate, usually because the E. coli strain was resistant to the first antibiotic given. (The patient must be treated immediately but it takes two days for the lab to get results, creating a window for error.) Mortality must be similarly high among untreated bacteraemias. Keefer, at the end of the pre-antibiotic era, found 35% deaths.
