SARS-CoV-2 nasopharyngeal vs Saliva – mini lit review

Update 2020-04-25: Health Technology Wales have released a much fuller review with some different papers. Table 2 very useful, will be great when we can split out “only” nasopharyngeal from throat + nasopharyngeal.
Update 2020-04-24: Centre for complex interventions released a higher level report summarising which tests reported to support which sample. are working up to provide SARS-CoV-2 full open-source testing. They’ve been offered a lot of saliva sampling kits. Is saliva a good choice vs oropharyngeal, buccal, mid-turbinate, nasopharyngeal? To help them out answering this question I did a mini litt review.

From what I’ve seen seems like taking samples from as many places as possible is a good idea but saliva has obvious large advantages. It’s simple for people to do, no swab needed, minimises risk of coughing and aerosolization, minimises PPE use, and no trained staff are needed (correct?).

An Italian hospital now requires 2 negative nasopharyngeal and 1 negative saliva before discharging people after finding some people with negative nasopharyngeal were still positive from saliva: Azzi et al. 14 April 2020 Saliva is a reliable tool to detect SARS-CoV-2. n=25 but from severely ill patients so does this generalise?

In the first patient, the salivary specimen was positive on the same day when a nasopharyngeal swab converted to negative, and this result was also confirmed after two days. The second patient showed positive results in two consecutive salivary swabs, while three consecutive respiratory swabs were negative on the same days.

Wang et al. 2004 Detection of SARS-associated coronavirus in throat wash and saliva in early diagnosis shows saliva has 1% of SARS virus in cell fraction with 99% in supernatant or N-acetyl-L-cysteine treated supernatant. Split between latter was N-acetyl-L-cysteine treated supernatant had x1.75 that of untreated supernatant. N-acetyl-L-cysteine breaks down mucus. Perhaps mucolytics could boost detection further from all samples? (links to UK DHSC site for crowd sourcing ideas)

One from Yale preprinted yesterday which is causing a stir Wyllie et al. 22 April 2020 Saliva is more sensitive and included 44 severely diseased patients in which they show:

  • higher titre in saliva
  • detected SARS-CoV-2 from saliva but not nasopharyngeal swabs from eight matching samples
  • nasopharyngeal swabs and not saliva from three matched samples

Whilst the data is interesting, the power is low and it points again to the fact that multiple sampling sites would be preferable but if saliva is all you can get then you will detect some cases. Again the time of the disease vs viral load in different sample sites will be really useful to know. We need a clinical trial on this.

There’s more papers to yet review in: under “Source of sample”

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