Genome detectives unravel spread of stealthy bacteria in a hospital

From Ed Yong. Fascinating summary including graphics from the original article: http://feedproxy.google.com/~r/NotRocketScience/~3/ABHdmEmP-SI/
See also Deb Blum's summary of coverage of this story at Knight Science Journalism Tracker.

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On 13 June, 2011, a woman was transferred to the National Institutes of Health Clinical Center with an infection of Klebsiella pneumoniae. This opportunistic bacterium likes to infect people whose immune systems have been previously weakened, and it does well in hospitals. In recent years, it has also evolved resistance to carbapenems – the frontline antibiotics that are usually used to treat it. These resistant strains kill more than half of the people they infect, and the new patient at the NIH hospital was carrying just such a strain.
She was kept to herself, in her own room. Any doctors or visitors had to wear gowns and gloves. The only contacts she had with other patients were two brief stints in an intensive care unit.
The woman eventually recovered and was released on 15 July. But by then, she had already spread her infection to at least three other patients, despite the hospital’s strict precautions. None of them knew it at the time, for K.pneumoniae can silently colonise the guts of its host without causing symptoms for long spans of time.
The second patient was diagnosed with K.pneumoniae on 5 August, ...