The secret to identifying people with methicillin-resistant Staphylococcus aureus isn’t right under our nose—it’s in it, new research suggests.

Across the U.S., roughly 1% of the population carries some form of MRSA around in their noses, according to researchers at Rhode Island Hospital. In their sample of 2,055 individuals, researchers found MRSA in the noses of 20% of long-term elder care patients. They also discovered higher rates among HIV patients (16%), outpatient kidney dialysis patients (15%) and inpatient kidney dialysis patients (14%). Having MRSA colonies in the nose does not indicate infection with the bug, researchers note.

Researchers also detected a vast difference in the number of colonies found (ranging from just three to more than 15 million) and in the types of MRSA found. Most patients had the fairly common USA100 strain found in health settings, but some patients—especially HIV patients—had the more virulent community-associated USA300 strain. MRSA in the nose has been associated with increased rates of MRSA-related pneumonia, bloodstream infection and surgical site infection, according to the report.

Further research is needed to learn why people have different strains and quantities of MRSA in their noses, researchers say. The report appears online and in the June issue of Infection Control and Hospital Epidemiology.