31 July 2010

News break: "Pig MRSA" ST398 involved in the death of a child?

The latest postings to the website of the CDC journal Emerging Infectious Diseases include a sad and very troubling letter from physicians in Lyon and Paris, reporting the death from necrotizing pneumonia of a previously healthy 14-year-old girl. That would be sad under any conditions, but here's what makes the death so troubling: It appears to have been caused by MRSA — but not by the community strain, USA300, that has been implicated in a number of deaths from necrotizing pneumonia. (Several such stories are told in SUPERBUG the book.)

Instead, her death appears to have been caused by infection with MRSA ST398 — the livestock-associated strain that was first noted in pigs raised with antibiotics, and the pig-farm workers caring for them, in the Netherlands 6 years ago, and that has since spread across the European Union, Canada and into the United States. (My 3-year archive of ST398 posts is here.)

This may be the first death associated with ST398, though I can't say that for sure as I am away from my big computer and working without my database. I'll update later today and confirm or knock that down.

The physicians say that the girl came in with flu-like symptoms and abdominal pain, was put on IV antibiotics (cefotaxime and amikacin), underwent an exploratory laparotomy that showed nothing, and shortly afterward developed acute respiratory distress and was put on a vent. A chest X-ray was shadowy on both sides. She went rapidly downhill and died 6 days later.

On analysis, the staph strain infecting her was ST398; there was no indication where she had picked it up. The strain had an unusual characteristic: It possessed the ability to make the cell-destroying toxin Panton-Valentine leukocidin, PVL for short, a genetic trick that until now has been a property only of community MRSA strains such as USA300. Though its role is disputed, PVL has been linked to community MRSA's ability to start infections on intact skin, and to the cellular damage that destroys children's lungs in cases of pneumonia caused by USA300. Until now, ST398 has been PVL-negative.

The physicians' letter is short and there's much more to find out about this case. But if the report and analysis are correct, this is bad news. One of the repeated themes in the 50-year evolution of MRSA has been its ability — all staph's ability — to promiscuously swap and share the bits of DNA that confer resistance and enhance virulence. Another, since the emergence of ST398, has been the potential peril of a staph strain adapting and mutating in the millions of farm animals around the world that are routinely given antibiotics — and that for the most part are not checked to see whether they harbor resistant organisms. If this report (and my interpretation) are correct, then those two trends are converging in a way that cannot bode well.

1 comment:

Peter Davies said...

This is indeed a regrettable event, but this blog (and particularly the title) is both erroneous and misleading. Firstly, the ST398 strain was NOT MRSA, but METHICILLIN SUSCEPTIBLE Staph aureus which was susceptible to all antibiotics tested except macrolides. Secondly, there is no evidence that exposure to pigs played any role in the case. Although pigs were first identified as a reservoir of ST398 MRSA, these strains are not limited to pigs, nor to livestock and the source of this infection is not yet known

Indeed, the t571 subtype of ST398 isolated is relatively uncommon in pigs in Europe, but was found to be common among two communities originating from the Dominican Republic, in Manhattan, NY and in the Dominican Republic (see http://www.cdc.gov/eid/content/15/2/pdfs/08-0609.pdf). MRSA isolates from pigs have uniformly been tetracycline resistant and PVL negative, unlike that from the reported case

As far as I am aware, there is yet to be a fatal case of ST398 MRSA infection reported, although pig industry workers in much of Europe and some other countries have apparently been commonly exposed to these organisms for several years.

Peter Davies BVSc
College of Veterinary Medicine
University of Minnesota, USA