MRSA Often Hides in Places Other Than the Nose

October 2011

Doctor's Bio

Pets can carry MRSA without looking or acting sick and can transmit it to humans. DR. ROSEN


Elsevier Global Medical News


WAILEA, HAWAII - If you think stuffing some mupirocin ointment up the nose of a methicillin-resistant Staphylococcus aureus carrier constitutes an adequate attempt at decolonization, think again.

MRSA likes to hide in other moist places besides the anterior nares, especially the throat, perineum, armpits, and under pendulous breasts. To determine if a patient with recurrent MRSA abscesses or other skin infections is truly a carrier and thus a candidate for decolonization, it's best to obtain cultures from all these sites, Dr. Theodore Rosen said at the SDEF Hawaii Dermatology Seminar.

He highlighted a large Belgian study that illustrates where MRSA hangs out. Investigators routinely screened for MRSA carriage by obtaining cultures from the nose, throat, and perineum of 2,060 hospitalized patients.

The patients had increased risk for MRSA carriage based on age over 70 years, transfer from another hospital, prior MRSA infection, an occupation in veterinary medicine, or other reasons. A total of 180 (9%) proved MRSA positive on culture. MRSA isolates were found in the nose in 89 patients, the throat in 65, and the perineum in 56 (Clin. Microbiol. Infect. 2009;15:1192-3).

A study of nearly 3,500 Swiss individuals, the great majority of them healthy, who were cultured from the nose and pharynx, showed 12.4% to be S. aureus carriers having the throat as their sole carriage site. Cultures obtained only from the nose would have misidentified them as noncarriers (Arch. Intern. Med. 2009;169:172-8).

A full MRSA decolonization effort may require 5-10 days of twice-daily mupirocin or an alternative agent for the nose, oral rinsing with 0.2% chlorhexidine three times daily for 7 days for the throat, and dilute bleach baths for 3 months to decontaminate carriage sites on the body.

This is a major undertaking. Fortunately, the recently released, first-ever clinical practice guidelines for the treatment of MRSA, issued by Infectious Diseases Society of America, recommend considering decolonization only as a third-line measure, noted Dr. Rosen, professor of dermatology at Baylor College of Medicine, Houston.

The first action to take in cases of recurrent MRSA skin infections, according to the guidelines, is patient education emphasizing proper wound care and personal and environmental hygiene (Clin. Infect. Dis. 2011;52:285-92). That means, among other measures, frequent hand washing, no reuse of towels or disposable razors, and regular cleaning of high-touch household surfaces including faucet handles, door knobs, shower stalls, and toilet seats.

Step two is to evaluate sex partners and other close personal contacts for MRSA carriage or infection and treat as appropriate. Although the IDSA guidelines don't mention pets, these animals can carry MRSA without looking or acting sick and can transmit it to humans.

"If Muffy carries MRSA and sleeps with someone who's having recurrent bouts of MRSA abscesses, Muffy needs to be treated. Veterinarians know how to look for this," Dr. Rosen said at the meeting, sponsored by Skin Disease Education Foundation.

He finds these two earlier steps often make decolonization unnecessary.

The difficulty of achieving successful decolonization is increased because of the emergence of mupirocin resistance worldwide. In a 2009 report, the mupirocin resistance rate in MRSA isolates from the United States stood at 14.7%. Laboratories don't ordinarily check S. aureus isolates for mupirocin resistance but can be asked to do so, as Dr. Rosen said that he routinely does now.

When the lab report shows a patient carries mupirocin-resistant MRSA, Dr. Rosen turns to retapamulin ointment (Altabax) instead. Retapamulin isn't indicated for use in the nose for MRSA decolonization, but there is no resistance to the topical antibiotic, and it is effective. It does, however, cause a mild burning sensation and irritation when applied in the nose, Dr. Rosen said.

When decolonization is attempted, the IDSA guidelines recommend dilute bleach baths for 15 minutes twice weekly for 3 months using a formula of 1 teaspoon of bleach per gallon of water, or one-quarter cup per 13 gallons or one-quarter bath tub.

Dr. Rosen disclosed he is on the speakers bureau for Graceway Pharmaceuticals and is a consultant to Graceway and Leo Pharmaceuticals. SDEF and this publication are owned by Elsevier.

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