Did MRSA kill an Ontario nurse?

Here is a story that was flagged by several commenters (welcome, Canadian readers), and is being reported by a number of Canadian news outlets: A nurse who worked in the critical care unit at Victoria Hospital in London, Ont. has died, possibly of MRSA, and the Ontario Ministry of Labor is investigating whether her death is an occupational exposure — that is, whether she caught the bug in the process of working in the hospital.

There's not a lot of detail in the stories published so far. The St. Thomas (Ont.) Times-Journal, the London (Ont.) Free Press and the Canadian Press suggest that the nurse was a patient in her own hospital and acquired the infection while a patient. The Toronto Globe and Mail, on the other hand, casts the story as the nurse working, becoming sick, and then becoming a patient.

Occupational infections with MRSA have certainly been recorded. A Texas firefighter and EMT died of invasive MRSA in 2006, and his widow alleged it was because of his exposure to MRSA patients; an Illinois EMT almost lost a leg to the infection in 2007.

Let's stipulate that this Ontario nurse's death is terribly sad. The question will be whether it is also scientifically confounding. A hospital is going to have a substantial background rate of MRSA, in infected patients, colonized patients and colonized personnel. If her death turns out to be caused by MRSA, it will be important to ascertain both the timeline — did she become sick while working, or while undergoing care for some other health problem — and also the microbiology: Did she have whatever strain is predominant in her hospital? Or was it on the other hand a strain that is circulating in the community (provided that community strains have not moved into hospitals in Ontario as they have in the US)?

That sort of microbiological differentiation provided an important clue in the death of Maribel Espada, a British nurse who died of invasive MRSA in 2006, six days after giving birth at the hospital where she worked. Unusually for the UK, Espada was infected with a PVL+ strain of MRSA, something that is very common in US community strains, but unusual in the UK until recently. That allowed her infection to stand out from the background, and suggested that she had been infected by a patient in her hospital:

The Health Protection Agency said it was investigating the possibility Mrs Espada caught PVL MRSA from a patient who died at the hospital in March.
A spokesman for University Hospitals of North Staffordshire NHS Trust said all staff who had come in contact with the two people originally diagnosed with PVL MRSA had been screened by the hospital's infection control team.
A further nine cases were subsequently identified, of which one was a former patient.
The eight other cases were either members of staff or people staff had come into contact with. (BBC News)