Preventing S. aureus SSI: Who does what? (part 2)

A month ago I blogged on the practices of pre-operative (or better peri-operative) treatment of nasal S. aureus carriage to prevent S. aureus surgical site infection (SSI) in orthopaedic or cardiothoracic surgery patients. The issue brought forward was that a “treat-all” (thus “screen none”) strategy is more feasible, more effective and cheaper than the “screen & treat” strategy. The latter strategy, is associated with less mupirocin exposure and thus less selective pressure for mupirocin-resistance genes. There was a poll with 2 questions. What is your current practice for patients undergoing orthopaedic or cardiothoracic surgery and what do you think the strategy should be, with 3 options for each question; “do nothing”, “screen & treat”, or “treat all”. Today the results.

There were 67 responses, and current practices were “do nothing” (n=27, 40%), “screen & treat” (n=27, 40%) and “treat all” (n=13, 20%). The preferred strategy was “do nothing” (n=3, 4%), “screen & treat” (n=34, 51%) and “treat all” (n=30, (45%). From those that “do nothing” now, 13 preferred to do “treat all” and 11 to do “screen & treat”. From those doing something, 6 of 27 wanted to go from “screen & treat” to “treat all”, and 2 of 13 vice versa.

So, if this were to be representative for the world, then there is an enormous potential for infection prevention (with 40% doing nothing), and there seems equipoise between the “screen & treat” and “treat all” strategy. And if there is equipoise, with no evidence of one strategy being better than the other, and both being considered standard care and safe, it is (or at least has been) relatively simple to do a cluster-randomized cross-over study, in which the effectiveness of both approaches can be compared, with a waiver for informed consent. Determination of outcomes is also relatively easy: all deep-seated S. aureus infections in the total populations undergoing surgery (primary endpoint), the hospital-wide occurrence of mupirocin and/or chlorhexidine resistance in invasive S. aureus isolates, the amount of mupirocin used and expenses (secondary outcomes). Who’s interested? Could be done as a superiority trial (“treat all” prevents infections compared to “screen & treat”) or a cost-minimisation study (no difference in infection rates, but “treat all” saves costs).

I also received questions about the safety of using mupirocin in all patients. For clarity, I am not a “mupirocin-resistance denier”. It exists and there are 2 important aspects to be considered: The risk of selection in an individual patient increases with the duration of mupirocin use in that patient, and with poor hygiene cross-transmission of resistant strains may occur. Yet, with a treatment duration of at most 5 days and with good hygiene I judge these risks to be low (at least where I work). Most reported situations of increased mupirocin resistance were in settings with either prolonged mupirocin use (such as in New Zealand, and more recently) or high levels of cross-transmission (such as London). But, as mentioned, if the prevalence of high-level mupirocn resistance in S. aureus and the occurrence of cross-transmission in the hospital are low, these risks can be monitored, and appropriate actions can be taken when needed.

We are investigating current practices in surgical infection prevention in European hospitals more formally. Let’s await results and then decide whether another trial is needed.

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One thought on “Preventing S. aureus SSI: Who does what? (part 2)

  1. To decolonize or not to do depends on the rate of deep incisional or organ/space SSI caused by S.aureus. Before applying a wide decolonization policy, it is necessary to ensure adequate compliance with more basic prevention measures such as chorhexidine skin asepsis, the administration “on time” of antibiotic prophylaxis and glycemic control. If the SSI rates are low (1%-2%) with these measures, is it really necessary to decolonize all patients? Mupirocin is used extensively in some countries such as Spain to control MRSA colonization. We daily use mupirocine to decolonize patients with MRSA nasal carriage. In countries with high MRSA prevalence (>25%), this important strategy can be lost because cross transmission of mupirocine resistant strains (now is less than 5% in our hospital). This is my biggest concern.
    Miquel Pujol, Clinical Head, Infectious Disease Service
    Bellvitge University Hospital, Barcelona. Spain

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