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Ten tips on MRSA in primary care

Consultant microbiologist Professor Barry Cookson offers advice on spotting and managing MRSA in primary care

Consultant microbiologist Professor Barry Cookson offers advice on spotting and managing MRSA in primary care

1 Think of methicillin-resistant Staphylococcus aureus (MRSA) infections in patients who have been admitted to healthcare establishments such as hospitals and some nursing homes. Hospital stays are now so short that infections, such as on surgical sites, may not have had time to develop until after discharge. Increasingly hospitals are screening patients before admission, and some are also screening upon discharge – for instance, from high-risk units.

A post-discharge surveillance system of surgical site infections is being considered.

2 MRSA infections can present with a variety of infectious conditions but most patients will be carrying it asymptomatically. At least three-quarters of those who acquire MRSA will only carry the organism, and may need no treatment at all, with the organism spontaneously clearing. In others, such as those being readmitted for surgery, it can pose a threat. This is a complex area, and GPs should liaise with the relevant hospitals and seek their expert advice on screening and eradication1,2.

Surgical infections are the most common cases but infections may also occur around dialysis or venous line sites, the urinary tract (especially

if there has been catheterisation), implanted devices such as cardiac pacemakers and joint replacements. However, they are possible in almost any other site.

3 Community-associated strains of MRSA (CA-MRSA), with no association with healthcare establishments, are still uncommon in the UK3. Such strains are more susceptible to antimicrobials (in particular ciprofloxacin, unlike most hospital MRSA), and may be distinguished from hospital MRSA by specialised typing tests in the Health Protection Agency's laboratory.

4 Some CA-MRSA strains can be extremely virulent and affect different types of patients from hospital MRSA. These more virulent strains carry a particularly potent toxin (Panton-Valentine Leukocidin, or PVL). PVL is more common in methicillin-sensitive Staphylococcus aureus (MSSA) cases in the UK, but even then it is carried by less than 2% of clinical isolates3. GPs should be aware that in certain countries, such as North America, PVL and CA-MRSA strains are common and are even causing cross-infection in hospitals. This has rarely been seen in the UK, but the HPA is watching the situation closely. GPs should be vigilant for PVL-related infections, particularly when patients return from affected countries.

5 PVL-related MRSA and MSSA should be considered when there are boils (furunculosis), carbuncles, folliculitis or cellulitis. Cutaneous lesions 5cm in diameter or larger are not uncommon. There may be pain and erythema that seem out of proportion to the severity of cutaneous findings. Recurrent infections are not uncommon, and it is also worth asking about similar infections in household and close contacts, for whom there is extensive advice available about treatment3. This should be considered where there is severe infection, recurrent infections or spread within these contacts.

6 PVL MRSA and MSSA can also cause invasive infections. These are serious and should be suspected in cases of invasive infection in immunocompetent people, particularly in the young. They comprise necrotising haemorrhagic pneumonia with a high mortality, which often follows a flu-like illness. It is not known what percentage are genuinely of viral aetiology and it is recommended that co-infection with a respiratory virus, including influenza A, is investigated. Oseltamivir prophylaxis should be considered if the index case is found to be influenza A positive. Other conditions that should be suspected include:

• necrotising fasciitis – can also be caused by Streptococcus pyogenes

• osteomyelitis

• septic arthritis

• pyomyositis

• purpura fulminans.

7 Be aware of the ‘five Cs' risk factors for MRSA and PVL-MSSA related disease3. These are:

• contaminated items like shared towels

• close contact, such as household or close social groups like military training camps, sports such as wrestling, American football, rugby, judo

• crowding – for example in prisons

• cleanliness – poor personal and environmental hygiene

• cuts and other compromised skin integrity.

Where there is a suspected outbreak, the local health protection unit needs to be involved as well as the local laboratory.

8 Appropriate clinical samples – pus, exudate from an abscess or similar sputum – from suspected cases should be collected and submitted to the local microbiology department for analysis. It is very important to take specimens when incising and draining abscesses. Moistened swabs should be used when sampling skin sites of any patient for MRSA or MSSA carriage. These can include nose, throat, perineum, axillae and lesions depending on local policies. PVL testing can be performed in the HPA's laboratory and also in some other centres around the UK. Your local laboratory will know the details of this, but your request forms should clearly indicate the reasons why you suspect PVL-related disease.

9 Minor skin and soft tissue infections (SSTIs) – folliculitis, furunculosis, small abscesses or boils without cellulitis – do not need systemic antibiotic treatment unless the patient is immunocompromised, an infant or is deteriorating clinically. Incision and drainage is the optimal management for abscesses. Moderate SSTIs including cellulitis and larger abscesses – especially those bigger than 5cm – should be treated with oral anti-staphylococcal antibiotics, in addition to appropriate drainage. The choice depends on susceptibility testing; flucloxacillin 500mg qds or clindamycin 450mg qds are recommended. There are many aspects of general care that are also important. Lesions should be covered, hygiene emphasised and patients advised to return if the lesions do not resolve or there is clinical deterioration. The agency's guidance, now available online3, has an example of a patient information leaflet and advice related to infection control in the home.

10 Urgent referral is needed if there is systemic involvement – hypo or hypertension, tachycardia, diarrhoea, vomiting suggestive of toxic shock, pyomyositis or necrotising conditions. If PVL-MRSA is suspected but admission to hospital is not warranted, rifampicin 300mg bd plus doxycycline (not for children under 12) or fusidic acid 500mg eight-hourly or trimethoprim 200mg 12-hourly or clindamycin 450mg qds alone can be used.

The most common PVL-MRSA seen currently in the UK is resistant to doxycycline and fusidic acid, so it is important that treatment is guided by results of antimicrobial susceptibility tests.

Other guidance on hospital treatment of severe infection is available on the internet.

Professor Barry Cookson is a consultant microbiologist and director of the laboratory of healthcare-associated infection at the Health Protection Agency

Competing interests None declared

MRSA

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