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

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

Study: From Delta to Omicron SARS-CoV-2 variant: switch to saliva sampling for higher detection rate. Image Credit: Marmolejos/Shutterstock
Examine: From Delta to Omicron SARS-CoV-2 variant: swap to saliva sampling for increased detection charge. Picture Credit score: Marmolejos/Shutterstock


At current, the usual detection approach for SARS-CoV-2 is the real-time polymerase chain response (RT-PCR) take a look at utilizing nasopharyngeal swab (NPS) samples. The gathering of nasal samples is usually an uncomfortable expertise for sufferers. Scientists revealed that saliva- and oropharyngeal swab (OPS) sampling are much less invasive strategies. One other benefit of saliva sampling is that the pattern may be self-collected and doesn’t require skilled healthcare individuals geared up with protecting measures.

Earlier research have revealed that OPS is much less delicate in comparison with NPS. Nonetheless, a mix of NPS and OPS sampling gives higher virus detection sensitivity in comparison with a single NPS sampling technique. Earlier research have indicated that saliva could possibly be an alternate pattern for the PCR-based detection of the SARS-CoV-2 virus. Importantly, a latest research reported that within the case of the SARS-CoV-2 Omicron variant, saliva specimens exhibited increased sensitivity in comparison with NPS.

A brand new research

A brand new research revealed on medRxiv* preprint server has centered on evaluating the relative efficiency of OPS, NPS, and saliva for the Delta and Omicron SARS-CoV-2 variants. On 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 take a look at have been requested to take part. The keen members have been supplied with a questionnaire that contained questions on their consuming, ingesting, chewing, or smoking standing half-hour previous to the Rt-PCR take a look at.

On 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 members, amongst which 124 have been male and 122 feminine, whose common age was 39 years. 155 members have been SARS-CoV-2 optimistic on not less than one of many three pattern sorts. 

Key findings

Researchers in contrast the Ct values of the three pattern sorts thought of on this research. They discovered increased statistically vital Ct values for OPS in comparison with NPS and saliva. This outcome 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 improve in sensitivity was noticed when OPS and NPS samples have been mixed. To know which sampling system is best 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. Moreover, 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. Nonetheless, within the case of detection of the Delta variant, no statistically vital distinction was discovered between NPS and saliva.

Apparently, a number of samples (two Delta and ten Omicron infections) examined adverse utilizing NPS and examined optimistic on saliva samples. Researchers performed follow-up testing amongst these candidates after two to 4 days and reported eleven sufferers to be optimistic for SARS-CoV-2. Amongst 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 take a look at had no influence 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 exams 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.

*Essential discover

medRxiv publishes preliminary scientific stories that aren’t peer-reviewed and, due to this fact, shouldn’t be considered conclusive, information scientific follow/health-related habits, or handled as established data.

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