How DNA Detectives Saved Dozens of Infants From a Deadly Breakout

When an outbreak of MRSA was detected in 12 babies at Rosie Hospital in Cambridge, UK, doctors panicked. The superbug is famously difficult to treat and particularly dangerous in infants. The risks were immediate; the implications dire. And how the hospital avoided catastrophe is a scientific sleuth story of the highest order.

MRSA—methicillin-resistant staphylococcus aureus to its friends—is a nasty bacterial infection that's resistant to many widely-used antibiotics, and it can be life-threatening if it breaches the skin. The problem is, it's extremely difficult to tell if cases are related or not: about one in 100 people carry MRSA on their skin without any health problems, so when 12 cases were detected there was a chance it was pure coincidence.

But scientists are loathe to defer to random chance, so they got to experimenting. Researchers quickly compared the entire genetic code of the MRSA bugs from each baby, building up a kind of family tree of the bug. It showed that they were dealing with the worst case scenario; the bugs were all closely, related and part of the same outbreak. One that could quickly spin out of control.

The ward was shut down and deep-cleaned to try and eradicate the infection for good; the babies were successfully treated. Everything was fine for two months.

Then another case appeared. The same DNA tests confirmed this, too, was part of the same outbreak. The team of researchers realized that the bug must be coming from somewhere within the system. Concerned, they tested 154 members of staff—and found a single member of the team who was carrying the MRSA bacterium.

Fortunately, the member of staff was treated, and all's returned to normal at Rosie Hospital. But the story represents the first time rapid genetic testing has been used to track—and then stop—an outbreak of MRSA, and it's something that's only just become possible.

Previously, DNA screening was prohibitively expensive and too slow to do this kind of thing; now, to sequence a bacterium costs tens of dollars and takes just hours. The ability to do tests like this has theoretically saved the lives of young children. Medical progress is amazing. [BBC]

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