MRSA--past, present, future

Autor: S W B Newsom
Rok vydání: 2004
Předmět:
Zdroj: JRSM. 97:509-510
ISSN: 0141-0768
Popis: Infections with methicillin-resistant staphylococci (MRSA) remain a major concern. A Medline search reveals 175 publications in the past eight weeks and the BMJ has produced two editorials in the space of a year.1,2 For the reason, readers need look no further than the article by Dr David Thompson on p. 521.3 In the intensive care unit (ICU) of his hospital, MRSA were present for 16.9% of available bed-days. The introduction of methicillin in 19604 heralded a period when staphylococcal infections were readily treatable. Such was the confidence in methicillin that the agent was sometimes sprayed into ward air to reduce staphylococcal infection and carriage amongst the newborn in hospital nurseries—with success.5 The occasional methicillin-resistant isolates, reported quite early on,6 were not notably troublesome. Methicillin is no longer made (having been replaced in the UK by flucloxacillin) but the term MRSA lives on. In the 1970s, nosocomial infection was not regarded as a high priority. Although the hospital building programme included isolation units (largely to replace the old ‘fever hospitals’), these were often not commissioned. In East Anglia, for example, 50% of the isolation beds in the new teaching hospital became a haematology ward, and in some of the ‘best buy’ hospitals some isolation beds were converted to other uses. Thus when major outbreaks of the ‘epidemic MRSA’ (EMRSA) occurred—such as that at Kettering7—isolation was impracticable and the strategy was to cohort infected patients and use a costly ‘search and destroy’ approach. Since then, EMRSA has affected most hospitals in the UK. A thoughtful article by Farrington et al.8 describes the Cambridge experience. Over 100 introductions of MRSA into the hospital between 1985 and 1995 were safely contained by a strategy of isolation and search and destroy, together with ward closures for cleaning; contacts were nursed in isolation until screened. However, in 1994 the isolation facilities were inadequate to cope with an outbreak of EMRSA on the geriatric wards involving 33 patients and 28 staff, and by early 1995 the number of ward closures was compromising the clinical work of the hospital. A revised policy reduced the stringency of the criteria for ward closure and allowed earlier reopening.9 Today the impact of nosocomial infection is properly acknowledged. National Guidelines for controlling MRSA were published in 199810 and are currently under revision. A two-tier control programme was recommended whereby hospitals that do not have MRSA should make every effort to keep it that way, and those where MRSA is endemic should concentrate resources on sensitive areas such as the ICU (though not at the expense of compromising patient care); before wards are closed there must be risk assessment and full consultation. Thompson’s article provides a worrying snapshot of the current general hospital intensive care ward—a site shown to be the most susceptible to nosocomial infections in a national survey.10 First, there is no possible way to control the introduction of MRSA from patients not previously known to be affected; only 21 of his 119 patients found to carry MRSA on admission were previously known to be carriers. Secondly, the 68 patients who acquired MRSA in the ICU were more ill, and remained there longer. The pathogenicity of the strains was reflected in the 17 bacteraemias encountered; 10 of these patients died. Clearly the existing guidelines are not fully practicable, and there has already been much discussion on this matter. Looking at the steadily increasing prevalence of MRSA despite efforts to control it, Barrett et al.11 concluded that existing strategies are not only ineffective but also sometimes counterproductive in terms of cost, side-effects of drugs used, and interference with the normal clinical work of the hospital. They considered that the correct approach was to concentrate on control of epidemics. But Farrington et al.12 judged this attitude too defeatist and reiterated their experience of the ten years when sporadic introductions of MRSA had been contained. Cooper et al.13 recently reviewed published work on the value of isolation. No well-designed studies were found on isolation as the only intervention. In four studies intensive control measures including isolation were effective, but in two others isolation made no difference. They concluded that, until the results of well-planned studies become available, the current guidelines should be followed. MRSA is troublesome worldwide and Scandinavian countries and the Netherlands have been most successful in containing it. A prevalence study on 9859 patients conducted in the Netherlands in 2000 showed a 0.03% carriage rate.14 Voss, from Nijmegen,2 accepts that this is an empirical finding but remains strongly in favour of these countries’ search-and-destroy approach combined with restrictive use of antibiotics, stating ‘While waiting for hard evidence we should have faith we are doing the right thing’. Meanwhile what of the ICU? A study from Australia on acquisition of MRSA in trauma patients in the ICU confirms the importance of length of stay as a risk factor.15 Thompson suggests that efforts at prevention in the ICU should be concentrated on long-term patients, and favours oral vancomycin. Whether or not to use antibiotics for prophylaxis of ventilator-acquired pneumonia has long been a controversial topic, with strong adherents to both sides. Vancomycin has already been used in Italy16 and Spain,17 and has been the subject of an editorial in the Journal of Hospital Infection.18 In the light of emerging vancomycin resistance in enterococci and the reduced susceptibility in some strains of MRSA19 such a strategy will require careful risk-assessment. Nonetheless, the Spanish study17 lasted four years and showed a reduction of MRSA in diagnostic samples from ICU patients from 31% to 2%. An outbreak involving vancomycin-resistant enterococci did occur but seems to have been managed without difficulty. What of the future? Many new avenues are under exploration. Tea-tree oil in a nasal application together with a body wash was shown to be as effective as mupirocin with antiseptic washes in the eradication of carriage of MRSA.20 Antiseptic-coated endotracheal tubes are undergoing trials. They appear to be well tolerated and retain antimicrobial activity in situ, but so far there are no comparative data on prevention of ventilator-acquired MRSA pneumonias.21 Other techniques under investigation include a hydrogen-peroxide-based gas to decontaminate the environment,22 air filtration units and diagnostic kits, phage therapy and, perhaps the most interesting, the ‘XF’ compounds—said to bind to the surface of bacteria and produce lethal amounts of oxygenated radicals on exposure to light energy. A search of Medline yielded no published data on this last approach. Whatever new answers emerge, we must hope they will not go the way of methicillin.
Databáze: OpenAIRE
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