The "vicious cycle" of HA-MRSA

In the new issue of Lancet Infectious Diseases there's a marvelous analytical review of the complex relationship between hospital overcrowding and understaffing and the rise of hospital-acquired MRSA.

You can feel intuitively that these phenomena must be linked:

• If a hospital has more patients, its staff will be more stressed;
• If they are more stressed, they may neglect handwashing and other infection-control measures;
• If budget shortfalls cause staff cuts, the remaining staff will be more stressed still;
• If infection control is neglected, more patients will acquire MRSA;
• Since MRSA patients are sicker and stay longer, more beds will be full;
• Since there are more patients, staff will be more stressed;
• Since MRSA patients are more costly, budgets will be more stressed.

And so on. Because it is a review article it is also an excellent guide to the medical literature on this aspect of the MRSA problem, with 140 cites.

The citation is: Clements, A. et al. Overcrowding and understaffing in modern health-care systems: key determinants in meticillin-resistant Staphylococcus aureus transmission. The Lancet Infectious Diseases 2008; 8:427-434.

Great post elsewhere on antibiotic use in animals

There will be a bit of a blog break, as I'm traveling for a week. But here as a walk-off is an excellent post from the marvelous public-health blog Effect Measure about the complexities (to be kind) of food companies declaring antibiotic use in food animals.

Very short version of the story: Massive chicken producer Tyson advertised its chickens as being "raised without antibiotics"; the chicken eggs were actually being treated with gentamicin before hatch (therefore technically not being "raised"; the US Department of Agriculture objected, then backed down, then objected again after Tyson's competitors acted on their own.

Tyson announced it is "voluntarily" withdrawing the label. Which is more than the USDA did, apparently, its hand having been forced by Tyson's competitors organized into the Orwellian-named Truthful Labeling Coalition (including Perdue Farms Inc., Sanderson Farms Inc. and Livingston, California-based Foster Farms). Perdue and Sanderson had sued over a label they considered "clearly false and misleading," and a federal judge agreed, ordering Tyson to stop them from running any advertisements with the claim last month. Now, belatedly, the USDA is acting.

The entire post is worth reading, as is Effect Measure (which is running on a "summer schedule" and therefore posting only once a day, thus making us all look bad. Hmm, perhaps a Public Health Blog Truthful Labeling Coalition is in order...)

Closing the loop: meat, meat-eaters, health-care workers

A posting on the international disease-alert mailing list ProMED led me to a scientific abstract presented at a European meeting this spring on the ST 398 MRSA strain. It adds another, quite unnerving piece to the emerging interplay of MRSA in pigs, humans who have close contact with pigs, humans who have contact only with pig meat, and health-care workers who treat those humans.

Brief precis: About a year ago, Dutch health authorities discovered that a patient who had come in for surgical debridement of a diabetic foot ulcer had an unrecognized MRSA strain in that ulcer. Subsequently, they discovered that four other patients and five health-care workers in the same institution were carrying the same strain. None of the patients reported any contacts with pigs (or calves, which have also been found to carry the strain). One of the health-care workers lived on a farm that raised pigs, but said that she had no contact with the animals in her daily life; nor did her partner.

The authors conclude:

While the source is not fully established it could be the HCW living on a pig farm. This outbreak makes clear that transmission on a larger scale can occur, even with NT-MRSA.

(Hat-tip to Helen Branswell of the Canadian Press for telling me about the ProMED report. And a note to loyal readers: The "MRSA in meat" story is being picked up by some US newspapers. Doesn't it feel good to know you've been reading about the issue here for months? And if you're a reader of Helen's work, months more? Of course it does.)

New blog on animal health including MRSA

Dr. J. Scott Weese of the Ontario Veterinary College (author of many important papers, discussed in many posts here, on MRSA in food and companion animals) has started a blog on animal-health issues. Here is a recent post on tracking down the source of a MRSA infection when there is a pet in the house.

The blog is called Worms and Germs and I've added it to the blogroll at right.

One more on MRSA in meat

It turns out that European governments — in contrast to the United States — are taking very seriously the emergence of MRSA in food animals and its potential for transfer to humans. (For background, posts here, here, here and here.)

How seriously? They're doing a sampling survey of pigs on farms across the European Union, at a cost of about $3 million in EC funds, with matching funds expected from each government.

The MRSA survey piggybacks (sorry) on a year-long survey of Salmonella incidence that the EC called for in September 2007. But in December, following publication of several significant papers about the ST 398 MRSA strain in pigs and pig farmers, the EC Directorate-General for Health and Consumer Protection pushed for an addition to the Salmonella study: a same-time sampling for the presence of MRSA strains in pig operations across 29 countries.

The sampling is taking place from January to December of this year, with results mandated by mid-2009, though individual country authorities may release data earlier if they choose. (In the wake of the finding of three ST 398 cases apparently caused by retail meat in the UK, the Soil Association has called on the British government to release whatever data it has ASAP. Before the EC decision, the UK government had refused to test its pigs; cf. these House of Lords minutes.)

Of note: The Soil Association is pressing the argument that ST 398 has developed in the setting of widespread use of antibiotics in food animals, and contends the strain's arising in the Netherlands is especially alarming because they have some of the lowest animal-antibiotic use rates in the EC it illustrates the difficulties that even a society conscientious about antibiotic overuse can have keeping track of veterinary applications. The Netherlands has been successful limiting overuse in humans, but has found controlling veterinary use much more of a struggle. (Thanks to the Soil Association for correcting my misunderstanding!)

MRSA in the food chain?

Behind the growing number of findings of MRSA in food animals and the humans who work with them — in the Netherlands, Canada and now in the US — there lurks a persistent concern that the meat of those animals could be a vector for MRSA transmission. Dr. J Scott Weese of the Ontario Veterinary College raised the possibility in a presentation I reported on at the International Conference on Emerging Infectious Diseases, and Dutch researchers raised it in a paper last year as well.

Until now, though, it has been a hypothetical concern, since the humans found with pig-associated MRSA (both the already-recognized community and hospital strains and the emerging ST 398 strain) have all been animal workers.

So much for hypothesis. The London newspaper The Independent is reporting that the ST 398 strain has sickened three patients in Scotland who have no connection to animal raising or slaughtering, suggesting their infections came from contact with raw meat.

All three patients, who were being treated in at least two different Scottish hospitals, recovered. Confirming the cases, Dr Giles Edwards, director of the Scottish MRSA Reference Laboratory, said: "A lot of the patients who got this infection in Holland and Canada have been people who work with animals, such as farmers and vets. But none of the three individuals in Scotland have been in contact with animals, not that we could find." (Byline: Martin Hickman)

The bug has not currently been found in pigs raised in England, but about two-thirds of pork sold in the UK is actually imported from the Netherlands. So the Soil Association (the British farming lobby) has asked the government to begin testing imported pork for MRSA strains. The British Food Standards Agency disagrees, however, telling the Independent it does not "see serious food safety issues."

Which is strikingly close to what CDC Director Dr. Julie Gerberding said in February when asked by the House Committee on Agriculture about the Dutch and Canadian reports:

... although the finding of MRSA in retail meats suggests a possible role for foodborne transmission, if such transmission occurs, it likely accounts for a very small proportion of human infections in the United States. (Letter .pdf archived here on the site of the National Pork Producers Council.)

Hmmm.

UPDATE: The Soil Association's statement, with some good additional references (including to a newspaper report by the Sunday Post two days before the Independent's) is here. More to come on this, I think.

Much more on MRSA and animals

Again from the 108th General Meeting of the American Society for Microbiology: new findings on the complex interaction of MRSA in humans, pets and food animals.

• From the University of Iowa, the first finding of MRSA in US pigs, on seven farms in Iowa and Illinois. The abstract doesn't say what subtype of MRSA was found, but a new strain of MRSA was found last year in pigs in the Netherlands and both that strain and a known human strain have been found in pigs in Canada. Carriage rates among the Midwestern pigs: from 100% of very young animals to 36% among adult swine. (Poster 983, first author AL Harper)
• From Nicholls State University and two veterinary practices in southern Louisiana, results of screening tests on pets show high rates of carriage of methicillin-resistant Staph species. The pets carried both S. aureus and S. intermedius. (Poster 1017, first author T. Rachal.) For an earlier post on pets harboring MRSA, look here.
• And from the University of Georgia, an analysis of MRSA strains isolated from 50 humans and 60 companion animals (dogs, cats, horses, birds) found the same strains in both: SCCmec type II, a hospital strain, and SCCmec type IV, the main community strain. Human carriage rates: 78% type IV, 22% type II. Animal carriage rates: overall, 40% type IV and 60% type II, but with some important differences between species — all of the cats and birds harbored type II, while the dog isolates were overwhelmingly II and the horses overwhelmingly IV. Of greatest importance, the types did not have identical resistance patterns: In humans, the type IV was sensitive to vancomycin and tetracycline, but the animal IV was sensitive to vanco only, suggesting that MRSA may be evolving differently in its transient animal hosts — an especial concern if the animal-carried strains pass back to humans. (Poster 1027, first author S. Sanchez.)

Antibacterial wipes - as reliable as they seem?

The general meeting of the American Society for Microbiology is taking place in Boston this week, and the agenda is rich with papers on MRSA. Here is one from today, with interesting and dismaying news.

A team from the Welsh School of Pharmacy at Cardiff University tested the killing efficacy of premoistened antibacterial wipes used to decontaminate surfaces in hospitals. No brand is specified in the abstract, but they are described as "commercially available wipes containing either disinfectant, detergent or natural antimicrobial" that are called for in the "disinfection regimens adopted in [intensive care units] in the UK."

The team, led by Dr. Gareth Williams and funded by the Wales Office of Research and Development for Health and Social Care, devised a three-step protocol to test the ability of the wipes to remove, kill, and prevent transfer of Staph aureus and MRSA from surfaces. To guarantee consistency and replicability, the protocol included the use of a device that mechanically rotated the wipes against contaminated surfaces at a particular pressure (100 grams +/- 5) and speed (60 rpm).

And the results are: not so great. The wipes did remove bacteria, but did not kill them. When the used wipes were pressed against agar plates, the plates grew bacterial colonies, raising the possibility that the wipes would transfer viable bacteria between surfaces in real-world use. The team's conclusion:

We recommend that a wipe is not to be used on consecutive surfaces, but only on a small area and discarded immediately after use.

The cite is: Determining the Ability of Surface Wipes to Remove, Kill and Prevent the Transfer of Staphylococcus aureus from Contaminated Surfaces. GJ Williams, SP Denyer, IK Hosein, DW Hill and JY Maillard. Poster 860, 108th General Meeting ASM.

(By the way, I am posting this using Blogger's new post-date utility. If it works, this post should magically appear at 1p EDT on 3 June. If it shows up early, someone will have some splaining to do.)