An interesting article published by Bastos and others in the Annals of Internal Medicine  investigated this issue.  

Nasopharyngeal swabs are the primary sampling method used for the detection of  SARS-CoV-2, but they are better performed by a trained healthcare professional and  require the wearing of PPE.  

This study looked at whether there was a difference in sensitivity for SARS-CoV-2  detection between nasopharyngeal swabs and saliva. 37 studies with 7,332 paired  samples were included. The results showed that the sensitivity of saliva was 3.4  percentage points lower than that of nasopharyngeal swabs.  

In those with a previously confirmed SARS-CoV-2 infection saliva sensitivity was 1.5  percentage points higher than that of nasopharyngeal swabs.  

Among persons with a previous SARS-CoV-2 diagnosis, saliva was 7.9 percentage  points less.  

In this subgroup, if testing 100,000 persons with SARS-CoV-2 prevalence of 1%,  nasopharyngeal swabs will detect 79 more, that is persons, with SARS-CoV-2 than  saliva but of course there would be an incremental cost per additional infection.  Naturally, saliva is easier for a patient to perform themselves and the study concluded  that taking all into account, although nasopharyngeal swabs are more sensitive, saliva  could be considered as an appropriate alternative.  

The London General Practice evaluates all forms of COVID-19 SARS-CoV-2 infection  and is happy to be at the forefront of testing. 

Dr Paul Ettlinger 

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