Maryn McKenna

Journalist and Author

MRSA colonization – the long-term risk

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One of the ongoing puzzles of MRSA’s behavior is the significance of colonization, that situation of MRSA living on the skin — or in the nostrils or other locations close to the body’s external surface — without causing illness. It’s not known how frequently MRSA colonization occurs, for one thing: The long-standing estimate of 1% of the population has been challenged by a number of recent studies.

Another persistent question has been whether the risk of illness and death changes as colonization continues. It has been established that up to one-third of newly colonized carriers will become seriously ill within a year of their acquiring the bug (Huang, SS. et al., Society for Healthcare Epidemiology of America Annual Meeting 2006, abstract 157 – not online that I can find)— but what happens beyond that? Does the risk of illness persist or decrease?

In Clinical Infectious Diseases, the same team that defined the risks of recent colonization report that there are significant risks to long-term carriage as well: 27% of invasive illness in the second year and 16% thereafter, based on a review of 281 patients who were followed for at least one and up to four years at Brigham & Women’s Hospital, a Harvard Medical School teaching hospital. These patients become very ill, and in addition use a significant amount of health-care resources:

At our hospital, there are 2–3 times as many hospital admissions involving patients previously known to harbor MRSA than there are hospital admissions of individuals who are newly detected as MRSA carriers each year.

What is the precipitating event that tips MRSA carriage over into MRSA illness? It may be health care. In other words, the long-term carriers do not become ill with MRSA disease and then come to the hospital. Instead, they come to the hospital for some other reason, and the surgery, IV placement, dialysis etc. they receive allows their MRSA strain to slip past the protective barrier of their skin and begin an invasive infection.

We submit that these high risks of MRSA infection among culture-positive prevalent carriers are not only preferentially detected because of hospitalization but may, in fact, be incurred because of the device-related, wound-related, and immunologic declines associated with a current illness.

This raises the question of whether any admitted patient found to be colonized should undergo the routine known as decolonization before any other procedures are performed — and whether institutions and insurance companies will be open to the additional hospital days and drug costs that will represent.

The cite is: Datta, R. and Huang, SS. Risk of Infection and Death due to Methicillin-Resistant Staphylococcus aureus in Long-Term Carriers. Clinical Infectious Diseases. 2008 47:176-81.

Isolation: Doesn’t work if healthcare workers contaminate themselves afterward

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In the new Emerging Infectious Diseases, there is a small but very smart study that ought to get wider play. It was done by a PhD candidate at University of North Carolina, Chapel Hill named Lisa Casanova, with the help of faculty and the local health department.

Background: In certain highly infectious environments — including in-hospital isolation — healthcare workers wear what is usually known as “personal protective equipment” or PPE. PPE generally includes gloves, gown and an eye shield, goggles or face-splash guard (also called “barrier precautions”) as well as a mask or a respirator (“respiratory protection”). PPE protects the healthcare worker while he or she is in the patient’s presence, but it poses a problem when the worker leaves that environment, because the PPE is likely to be carrying the disease organism on its surface. If the worker doesn’t doff the PPE very carefully, he or she might contaminate himself/herself and become infected or colonized, or spread the organism further in the healthcare environment.

This accidental contamination was a significant problem in the 2003 SARS epidemic — so after SARS was over, the Centers for Disease Control and Prevention came up with a recommended procedure for taking off PPE (on this page, half-way down). Casanova decided to test how well the protocol actually works.

Answer: Not so much. She had 10 volunteers (men and women, left- and right-handed) dress in PPE, contaminated the equipment in certain spots (“front shoulder of gown, back shoulder of gown, right side of N95 respirator, upper right front of goggles, and palm of dominant hand”) with a benign virus, had the volunteers take off their PPE, and then tested them for the virus’s presence. Results:

Transfer of virus to both hands, the initially uncontaminated glove on the nondominant hand, and the scrub shirt and pants worn underneath the PPE was observed in most volunteers.

Casanova recommends changes: additional PPE; different PPE and doffing protocols, such as are used in surgical suites; or PPE impregnated with antimicrobials. (#1 and #3 of course would be more costly; #2 would require procedural change but not necessarily additional garments).

She also raises a vital ongoing issue for MRSA infection control: that healthcare workers may not be punctilious about hand hygiene because they believe that gloves are adequate protection. Only, as this study demonstrates, they are not:

This study also indicates the need for continued emphasis on hand hygiene. A barrier to improving hand hygiene compliance rates is the belief that gloves make hand hygiene unnecessary (14). This is contradicted by our study and others showing that organisms can spread from gloves to hands after glove removal (15). Even if double gloving is incorporated into protocols for PPE use, it is not a substitute for proper hand hygiene.

The cite is: Casanova L, Alfano-Sobsey E, Rutala WA, Weber DJ, Sobsey M. Virus transfer from personal protective equipment to healthcare employees’ skin and clothing. Emerg Infect Dis. 2008 Aug; [Epub ahead of print]

The “vicious cycle” of HA-MRSA

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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

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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

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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

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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

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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!)