Nasal Screening for MRSA: Different Swabs – Different Results!

Abstract

ObjectivesSwab-based nasal screening is commonly used to identify asymptomatic carriage of Staphylococcus aureus in patients. Bacterial detection depends on the uptake and release capacities of the swabs and on the swabbing technique itself. This study investigates the performance of different swab-types in nasal MRSA-screening by utilizing a unique artificial nose model to provide realistic and standardized screening conditions.MethodsAn anatomically correct artificial nose model was inoculated with a numerically defined mixture of MRSA and Staphylococcus epidermidis bacteria at quantities of 4×102 and 8×102 colony forming units (CFU), respectively. Five swab-types were tested following a strict protocol. Bacterial recovery was measured for direct plating and after elution into Amies medium by standard viable count techniques.ResultsMean recovered bacteria quantities varied between 209 and 0 CFU for MRSA, and 365 and 0 CFU for S. epidermidis, resulting swab-type-dependent MRSA-screening-sensitivities ranged between 0 and 100%. Swabs with nylon flocked tips or cellular foam tips performed significantly better compared to conventional rayon swabs referring to the recovered bacterial yield (p<0.001). Best results were obtained by using a flocked swab in combination with Amies preservation medium. Within the range of the utilized bacterial concentrations, recovery ratios for the particular swab-types were independent of the bacterial species.ConclusionsThis study combines a realistic model of a human nose with standardized laboratory conditions to analyze swab-performance in MRSA-screening situations. Therefore, influences by inter-individual anatomical differences as well as diverse colonization densities in patients could be excluded. Recovery rates vary significantly between different swab-types. The choice of the swab has a great impact on the laboratory result. In fact, the swab-type contributes significantly to true positive or false negative detection of nasal MRSA carriage. These findings should be considered when screening a patient.

Improved microbiological diagnostic due to utilization of a high-throughput homogenizer for routine tissue processing

“…Swabs and, to lesser extent, tissue biopsies are used for microbiological analyses from sites of infection. For swab-based analyses, the microbiological yield is dramatically influenced by the sampling device itself (Warnke et al, 2014a(Warnke et al, , 2014b, as well as by the sampling technique (Warnke et al, 2014c). For tissue specimen analyses, the microbiological yield detectable in the laboratory is primarily determined by the processing of the sample, since detection only depends on the microbiological quantities present in the sample and not on the uptake and release capacities of the sampling device.…”

Recurrent mucocutaneous infections caused by PVL‐positive Staphylococcus aureus strains: a challenge in clinical practice

“…It has been shown that there are significant differences between different types of swabs in terms of true‐positive or false‐negative detection rates of nasal MRSA colonization . Under study conditions, the highest sensitivity was achieved using a flocked swab combined with Amies liquid medium . Such a swab may therefore be recommended in order to increase the sensitivity of pathogen detection.…”

Pilot Study to Detect the Presence of MRSA among Healthcare Workers Who Practice Ablution

“…The nose is the main reservoir for S. aureus, which can be distributed into the respiratory tract and to the surface of the skin and even to the surrounding air during exhalation [22]. However, colonization of S. aureus can be seen in several human body sites, the anterior nares are the most common carriage site for this organism [23].…”

“…Given that MRSA is a cross cutting problem affecting both health-care settings as well as the community, it is essential to include evidence from these settings too. Secondly, the small size of the study (22 …”