Remember all those outbreaks of a hospital bug called C. diff a few years back? At its peak in 2007, this bug was linked to 7,916 deaths in England alone. Since then, deaths linked to C. diff have fallen. But scientists believe this micro-organism continues to be a threat - and it's easy to see why when you look at some new research from the Sanger Institute in Cambridge.
They found the global epidemic in the early to mid-2000s, that included the UK, was caused by the spread of two different but closely related strains of the bacterium, rather than one as was previously thought.
They've done an incredible forensic job of tracking where the global outbreak started and how it spread by using the latest technology to analyse the DNA of bugs found in samples from patients around the world.
The first strain, FQR1, originated in the USA and spread across the country and then to Switzerland and South Korea. The second strain, FQR2, originated in Canada and spread rapidly over a much wider area, throughout North America, Australia and Europe.
The spread of C. diff into the UK was caused by long-range transmission from the US - there were separate bursts leading to infections in Exeter, Ayrshire and Birmingham, leading to outbreaks in many hospitals in the mid-2000s.
Two reasons why this bug spread so widely.
First, it produces spores which last for a long time and remain infectious - that means they can be spread over long distances. And secondly, both these strains became genetically resistant to an antibiotic called fluoroquinolone which had been widely used to treat infections but became pretty much useless.
Dr Trevor Lawley, from the Wellcome Trust Sanger Institute says: