Saliva tests may be as good as nasal swabs

Research at laboratories in Auckland, Wellington and Dunedin suggests saliva tests are just as effective at detecting Covid-19 as nasal swabs.

Technicians at labs in those three cities checked 196 paired samples of Covid tests, after subjects did both a saliva and a nasopharyngeal swab.

Of those, 46 tests (23%) were recorded as positive, from either sample type, an article published in the New Zealand Medical Journal today said.

Of the positive tests, the nasopharyngeal swabs had a 93% success rate and saliva tests a 91% hit rate, which researchers said indicated no significant difference in performance between sample types.

"In summary, we found that saliva is an equivalent sample type to nasopharyngeal swabs for the detection of SARS-CoV-2 in our laboratories using multiple assay combinations and is suitable for use as a diagnostic and surveillance test."

New Zealand was slow to adopt saliva testing for Covid-19, despite strenuous calls for its widespread introduction, and self-administered nasal rapid antigen tests remain the backbone of the country’s Covid-testing programme.

The authors, which included several Southern Community Laboratories staff, warned that their study was based on a small sample and there were quite large differences in positivity among the participating laboratories.

"Further ongoing studies would be useful to assess the impact of vaccination status, variants and time from onset of infection on detection in different anatomical spaces."

The article said the New Zealand results matched the findings of similar studies overseas, but noted that results could differ depending on technology and correct use of each type of test.

"In three instances, saliva samples were positive where nasopharyngeal swabs were negative, and in four instances the nasopharyngeal swabs were positive and the saliva samples were negative.

"Comparing the assays, there was no statistically significant difference between the performance of samples at any laboratory or assay combination."

Meanwhile, a further 6152 new community cases of Covid-19 were reported in New Zealand yesterday, 527 of which were from Otago and Southland.

The number of people in hospital in the region who had Covid-19 dropped yesterday from 36 to 28, but two wards at Southland Hospital remained closed to visitors after Covid-19 and influenza exposure events.

The Ministry of Health reported a further 47 people had died who were Covid-positive, two of whom were from Southern.

mike.houlahan@odt.co.nz

 

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