Qualitative and (semi)quantitative characterization of nasal and skin methicillin-resistant Staphylococcus aureus carriage of hospitalized patients.

The objective of this study was to systematically investigate the carriage pattern and load of newly identified methicillin-resistant Staphylococcus aureus (MRSA) colonized or infected patients before any decolonization took place. Cultures of wounds (38%), of sputum (16%) or throat (10%) and of urine (10%) most frequently gave the initial positive MRSA result. Samples from nose, forehead, neck, axilla, and groin were obtained to determine the extent of nasal and extranasal colonization. Fifty-six (69%) of the screened patients proved to be MRSA positive at one or more of these sample sites, and 53 (65%) were extranasal carriers. The proportions positive for cultures of the nares, forehead, groin, neck and axilla were 54%, 51%, 38%, 35%, and 28%, respectively. The most sensitive screening method (96% sensitivity) was to take a combination of cultures from the nares, forehead and groin. Out of the 56 patients (100% sensitivity) this combination revealed 10 more MRSA-carriers than testing the nose alone (79% sensitivity). But the number of study patients was relative small. Therefore we cannot give general recommendations for MRSA screening on the basis of these results. For our hospital we concluded to take a combination of three screening samples to detect MRSA-carriers. Beside the MRSA-carriage pattern we report about the quantitative whole-body colonization. Out of 41 patients colonized on the forehead, a median of 20 MRSA/24 cm2 was obtained on contact agar plates. On the neck (n = 28), an identical value was found. The median MRSA levels for the nose (n = 44), the groin (n = 31), and the axilla (n = 23) were 80, 50 and 50 cfu/swab streak. The MRSA load varied widely from 1 to more than 100 colonies per culture. Further studies must show whether the individual number of MRSA cultured from different body sites is relevant for transmission, for acquiring infections or for decolonization efficacy.