MRSA colonization: what being a carrier means

MRSA colonization means MRSA is present on your body but is not causing disease. There is no pain, no pus, no fever. Around one in three people carry ordinary Staphylococcus aureus in the nose, and roughly 1–2% of the general population carry the methicillin-resistant form. A positive screening swab puts you in that second group. It is a risk flag, not a diagnosis.

The distinction drives everything that happens next — whether you need antibiotics, whether you are isolated in hospital, and whether anyone treats you at all.

• Colonized — MRSA sits on intact skin or in the nostrils. You feel normal. No antibiotics are usually needed. Precautions exist to protect other people, not to treat you.
• Infected — MRSA has crossed the skin barrier. You see a boil, an abscess, a spreading red area, or feel systemically unwell. This needs treatment, often drainage plus antibiotics.

If you are unsure which you are looking at, the symptoms guide walks through what an early MRSA lesion looks like.

The anterior nares — the front of the nostrils — are the classic reservoir, which is why the standard screening test is a nasal swab. But MRSA also colonises the throat, armpits, groin, perineum, and any chronic wound, ulcer, tracheostomy site or catheter exit site. Some hospitals swab several of these sites, not just the nose, because nose-only screening misses a meaningful share of carriers.

A swab is rotated gently inside each nostril for a few seconds. It is uncomfortable at most, and never painful. Two testing routes follow:

• Culture — the sample is grown on a selective plate for 24–48 hours. Slower, but it yields a live isolate that can be tested against different antibiotics.
• PCR — the sample is tested for the mecA/mecC resistance gene directly. Results in one to two hours, which is why it is used for emergency admissions and pre-operative screening.

A positive result means MRSA was detected. It does not tell you when you acquired it, how long it will last, or whether you will ever become ill. More detail on the testing itself is on the MRSA test page, and nose-specific issues on MRSA in the nose.

Screening exists to protect the person being admitted and everyone else on the ward. Typical triggers are planned surgery — especially orthopaedic, cardiac and vascular procedures where an implant is going in — admission to intensive care, dialysis, transfer from another hospital or care home, and any previous MRSA history. Policies vary: some hospitals screen universally on admission, others target high-risk groups only.

There is no fixed answer. A proportion of people clear MRSA within weeks with no intervention at all. Others carry it for years. Follow-up studies of hospital patients have found that around half are still positive a year after their first positive swab. Carriage persists longer when there is a chronic wound or leg ulcer, an indwelling line or catheter, eczema or other broken skin, repeated antibiotic exposure, or ongoing dialysis.

Two consecutive negative swabs taken at least 48 hours apart, off any decolonisation treatment, is the usual practical standard for declaring someone clear.

Yes, though the risk to others is considerably lower than from an open, draining wound. MRSA transfers from carrier hands to door handles, phones, towels and other people's skin. The precautions are the ordinary ones: handwashing, covering cuts and not sharing personal items. You do not need to stay away from work, school or your family because of a positive screening swab.

Clearing carriage is not routine. Mupirocin resistance rises when the ointment is used widely and repeatedly, and carriage often returns after a course, so clinicians reserve decolonisation for situations where it changes an outcome:

• Before surgery involving an implant or an open chest.
• Before or during an intensive care or dialysis episode.
• During a ward or household outbreak.
• For someone getting repeated skin infections, often treating the whole household at once.

A typical course is five days of mupirocin nasal ointment twice or three times daily, combined with daily chlorhexidine body washes.