Microbiology transport systems: not all are created equal

In light of emphasis being placed on quality in the clinical laboratory, and given the increased awareness of the importance of the pre-analytical phase of specimen processing, the selection of the most appropriate collection device cannot be overemphasised. If the pre-analytical step is performed with suboptimal quality, even the highest standards of laboratory quality management cannot compensate for the initial flaws. In clinical diagnostics, successful sampling and transfer of the pathogen to the laboratory is critical; if this step fails, no amount of sophisticated automation will enable a diagnosis, and this might lead to inadequate treatment of the patient. A transport system that will maintain viability of the organism for 24 to 48 hours becomes a necessity, as the need to transport these specimens a greater distance becomes a reality. Tissue biopsy and fluid aspiration methods are preferred for collection of clinical samples; however, swab transport systems are commonly used due to their low cost and ease of use, and the ability to maintain viability for aerobic, anaerobic and fastidious microorganisms over extended times.¹

Collection and transport of bacterial specimens to the laboratory is a critical component in the success of the diagnostic process. Transport time and temperature are now major concerns as the original concept and design of swab transport devices is 30–40 years old and they were developed in a time when the patient was only minutes away from the laboratory. Swabs are a much used type of sampling device, and the swab material plays a major, but often overlooked, role in sampling. The preservation and viability of organisms must be assured. Transport swabs must be seen as a critical component of the diagnostic pathway. Failure to ensure viability of microorganisms at the pre-analytical stage will have an adverse effect on any relevant clinical information received from the investigation.

Parameters such as collection efficiency must be ascertained as well as the ability of the swab to release its contents onto the medium. Other factors such as the ability to maintain moisture within the swab is critical to the survival of some organisms. This is certainly more relevant today with consolidation of laboratories resulting in considerable delay from the point of collection to sample processing in the laboratory; desiccation of cells on the swab can dramatically reduce survival. It is a well-known fact that Staphylococcus aureus can withstand desiccation,² whereas Neisseria gonorrhoeae is very sensitive to dehydration.³ To prevent cellular death on swabs and also to minimise the overgrowth of commensals that coexist with the test organism, transport media are used. The question pertinent to this study is, how certain are laboratories in their ability of their procured swabs to ensure the survival of fastidious organisms over a time period of 24 to 48 hours?