COVID-19: guidance on alternative swab types and transport media
Updated 29 March 2021
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Difficulties with supply chain for key virological testing components such as swabs and transport medium have led to local variations in practice with respect to sampling which may also impact on PCR diagnostic test performance.
In addition, it is important that we make best use of our available testing capacity by utilising a single swab wherever practical. To mitigate the supply issues, recommendations are two-fold:
1.Reduce demand for swab usage by:
- using a single swab for sampling throat then nose
- reduce level of testing for non-COVID related viruses (for example influenza and other respiratory viruses, as per Royal College of Pathologists guidance
2.Use alternative swabs and transport medium in accordance with a locally validated laboratory strategy for preferred and secondary source of both swabs and transport medium. Recommendations for alternatives are provided below.
Alternative swab types
Multiple reports indicate that flocked or rayon or Dacron swabs are the preferred types for collecting respiratory samples, with decreased sensitivity with cotton swabs. Urethral, pernasal or mini-tip swabs may also be alternatives if standard sized swabs are not available. Dry swabs are not optimal for respiratory samples but can be used if no alternative is available. ‘Charcoal’ swabs (such as swabs transported in a charcoal-containing medium) are not suitable.
Swabs with polystyrene shafts should be used, as swabs with wooden shafts may contain PCR inhibitors and may also be a safety issue, especially for patients who are self-swabbing or when used to swab young children.
Alternative transport medium
Laboratories can use alternatives to Viral Transport Medium (VTM) subject to local validation, including Universal Transport Medium (UTM) or liquid Amies medium without charcoal (Amies medium with charcoal is not suitable). If necessary the following can be used as alternatives (in order of hierarchy): Phosphate Buffered Saline (PBS) with a protein source such as albumin or bovine serum, PBS alone, saline, or no transport medium (such as a dry swab).