Screening of MRSA: A Comparison between One and Multiple Sites Sample Collection Using the New ESwab™ MRSA Collection Kit

Abstract

Background: A new ESwab™ MRSA Collection Kit (Copan, USA) was developed to collect and transport clinical specimens for the isolation of MRSA. This kit comprises of three regular size flocked swabs that allow collecting up to three specimens from different sites of the same patient and a tube with 1ml modified liquid Amies medium for the pooling of samples. The aims of this study were to evaluate the new ESwab™ MRSA Collection Kit for MRSA screening and to compare one site versus multiple sites sample collection for the screening of MRSA.

Methods: A total of 20 patients and 10 healthcare professionals from Hospital São Paulo (Brazil) were screened for MRSA colonization. The samples were collected from each patient/ healthcare professional, using two different methods: 1) Single site collection (anterior nares) using one Amies Agar Gel swab (Copan, USA) and 2) Multiple sites collection (anterior nares, throat, axilla) using the ESwab™ MRSA Collection Kit. After swabbing the patients, the Amies Agar Gel swabs were vortexed in saline while the 3 ESwabs™ from each patient were vortexed in the same Liquid Amies medium, resulting in a pool of samples from the same patient. Three aliquots of 200μl were collected from each medium and tested for MRSA by three different methods: real time PCR, direct culture using a CHROMagar™ MRSA agar plate (Paris, France) and pre-enrichment culture using TSB broth medium and a CHROMagar™ MRSA agar plate. Two MRSA clones previously identified and two ATCCs strains were used as controls.

Results: Among the 20 patients and 10 healthcare professionals collected, nine were MRSApositive. Results from both collection methods and from the three MRSA isolation tests were concordant in 100% of the cases.

Conclusion: Our study corroborates the literature by proving that the essential site to sample for MRSA screening is the anterior nares. On the other hand it is common practice in countries outside of the USA to collect samples from multiple sites. For this purpose the new ESwab™ MRSA Collection Kit™ proved to be an excellent choice for MRSA screening, allowing the pool of multiple specimens, limiting the test costs and at the same time, broadening the screening capabilities.

INTRODUCTION 

The transmission of MRSA and the risk of MRSA infection can only be addressed effectively if measures are taken to identify MRSA carriers as potential sources and treating them to reduce the risk of transmission. This requires screening of patient populations for MRSA carriage either before or on admission, to identify carriers and implement a decolonization regimen.

The normal habitat of S. aureus, including MRSA, is human skin, particularly in the anterior nares, axilla, throat and perineum. Clinical infection with MRSA occurs either from the patient’s own resident MRSA or by cross-infection from another person, who could be an asymptomatic carrier or have a clinical infection. Patients with a clinical infection caused by MRSA should, where possible, be cared for in a single-room isolation to minimize the risk of transmission.

The logical conclusion of risk factor assessments and the results of modeling studies is that the most appropriate approach to the reduction in MRSA carriage in the population, and resultant MRSA infections, is the universal screening of all admissions to hospital.

The essential patient site to sample is the anterior nares, as this is the most common carriage site for MRSA. Most patients positive at other sites have positive results from nose samples; However, a small proportion do not. For this reason, countries outside USA are recommending screening all patients admitted to the hospital by swabbing three different sites of the patient. This clearly had major resource implications for initial investment, mainly in terms of laboratory staff time and high costs of the laboratory tests.

In order to reduce these laboratory costs and follow the MRSA screening recommendations, a new ESwab™ MRSA Collection Kit (Copan, USA) was developed. This kit comprises of three regular size flocked swabs that allow collecting up to three specimens from different sites of the same patient and, a tube with 1ml modified liquid Amies medium for the pooling of samples.

The aims of this study were to evaluate the new ESwab™ MRSA Collection Kit for MRSA screening and to compare one site versus multiple sites sample collection for the screening of MRSA.