Health and Fitness

The relative performance of OPS, NPS, and saliva for detecting the Delta and Omicron SARS-CoV-2 variants

Scientists have labored extensively onerous to comprise the coronavirus illness (COVID-19) pandemic attributable to the speedy transmission of extreme acute respiratory syndrome coronavirus-2 (SARS-CoV-2). They developed diagnostic kits for speedy detection of the virus and developed many pharmaceutical and non-pharmaceutical means to scale back transmission of the virus in addition to the mortality fee.

Study: From Delta to Omicron SARS-CoV-2 variant: switch to saliva sampling for higher detection rate. Image Credit: Marmolejos/Shutterstock
Study: From Delta to Omicron SARS-CoV-2 variant: swap to saliva sampling for greater detection fee. Image Credit: Marmolejos/Shutterstock


At current, the usual detection method for SARS-CoV-2 is the real-time polymerase chain response (RT-PCR) check utilizing nasopharyngeal swab (NPS) samples. The assortment of nasal samples is commonly an uncomfortable expertise for sufferers. Scientists revealed that saliva- and oropharyngeal swab (OPS) sampling are much less invasive strategies. Another benefit of saliva sampling is that the pattern will be self-collected and doesn’t require skilled healthcare individuals outfitted with protecting measures.

Previous research have revealed that OPS is much less delicate in comparison with NPS. However, a mix of NPS and OPS sampling gives higher virus detection sensitivity in comparison with a single NPS sampling methodology. Previous research have indicated that saliva might be an alternate pattern for the PCR-based detection of the SARS-CoV-2 virus. Importantly, a current research reported that within the case of the SARS-CoV-2 Omicron variant, saliva specimens exhibited greater sensitivity in comparison with NPS.

A brand new research

A brand new research revealed on medRxiv* preprint server has targeted on evaluating the relative efficiency of OPS, NPS, and saliva for the Delta and Omicron SARS-CoV-2 variants. In this research, people who have been current on the screening heart in Ypres, Belgium, between December 3rd, 2021 and February 15th, 2022, for a SARS-CoV-2 RT-PCR check have been requested to take part. The prepared contributors have been supplied with a questionnaire that contained questions on their consuming, ingesting, chewing, or smoking standing half-hour previous to the Rt-PCR check.

In this research, nurses individually collected OPS and NPS samples, whereas saliva samples have been collected in a CE-labeled sterile buffer-free container by spitting. To establish the SARS-CoV-2 variants that contaminated every participant, scientists carried out SARS-CoV-2 whole-genome sequencing (WGS). Scientists included a complete of 246 contributors, amongst which 124 have been male and 122 feminine, whose common age was 39 years. 155 contributors have been SARS-CoV-2 optimistic on at the least one of many three pattern sorts. 

Key findings

Researchers in contrast the Ct values of the three pattern sorts thought-about on this research. They discovered greater statistically vital Ct values for OPS in comparison with NPS and saliva. This consequence strongly signifies decrease sensitivity and adverse prediction worth (NPV) no matter the kind of SARS-CoV-2 variant.

Out of 155 SARS-CoV-2 optimistic samples, 152 samples have been precisely detected for SARS-CoV-2 virus utilizing each OPS and NPS samples. A marginal enhance in sensitivity was noticed when OPS and NPS samples have been mixed. To perceive which sampling system is healthier for the detection of the SARS-CoV-2 variants, scientists in contrast the efficiency of NPS and saliva in each Delta and Omicron teams.

They noticed a statistically vital decrease Ct worth for all examined genes in NPS samples, in comparison with saliva samples, for each Delta and Omicron variants. Additionally, detection of the Delta variant was comparable between NPS and saliva. Importantly, researchers discovered a better sensitivity for the detection of SARS-CoV-2 Omicron variants utilizing saliva samples in comparison with NPS. However, within the case of detection of the Delta variant, no statistically vital distinction was discovered between NPS and saliva.

Interestingly, a number of samples (two Delta and ten Omicron infections) examined adverse utilizing NPS and examined optimistic on saliva samples. Researchers carried out follow-up testing amongst these candidates after two to 4 days and reported eleven sufferers to be optimistic for SARS-CoV-2. Among these eleven candidates, ten have been SARS-CoV-2 optimistic on the NPS samples along with saliva specimens. Scientists carried out logistic regressions and revealed that consuming, ingesting, chewing, or smoking, half-hour earlier than the SARS-CoV-2 check had no affect on sensitivity for all three varieties of samples.


The authors of this research revealed that saliva samples are superior to NPS for detecting the SARS-CoV-2 Omicron variant. The present research additional revealed that RT-PCR checks utilizing saliva samples are extra delicate for the detection of the early part of Omicron an infection. The OPS pattern is the least delicate specimen for PCR-based detection of the SARS-CoV-2 virus in comparison with the NPS and saliva specimen.

*Important discover

medRxiv publishes preliminary scientific stories that aren’t peer-reviewed and, due to this fact, shouldn’t be thought to be conclusive, information medical apply/health-related conduct, or handled as established info.

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