Saliva is a biologic fluid secreted from salivary glands, which is similar to serum and other body fluids and contains biomolecules such as DNA, RNA, microRNA, proteins, metabolites etc. Hence, studies are being done using saliva for diagnosis of COVID19.
Why to prefer saliva over nasopharyngeal swab?
- Saliva is non invasive and hence painless – there are two samples which are being used in detection of COVID 19 that is blood and deep nasopharyngeal swab. Both of these modalities of collection cause pain to patients.
- Saliva on the other hand can be collected without causing any discomfort to the patients and thus multiple samples of saliva can be collected if required.
- Easy to collect i.e. not technique sensitive – There is no need of trained personnel for collecting saliva samples.
- Less chances of disease transmission to the healthcare worker while collecting sample – During sample collection using nasopharyngeal swab the healthcare personnel has to come in close contact with the patient, which increases the possibility of disease transmission. Such chances of disease transmission decrease as saliva can be self -collected by patients.
- Saliva testing requires less resources, personal protective equipment, and personnel than nasopharyngeal swabbing – financial feasibility.
- Saliva can be pooled easily for screening of larger population.
The SARS-CoV-2 RNA is generally detectable in saliva specimens during acute phase of infection. Salivary based diagnostic aids detect this viral RNA and convert it to DNA, because only DNA can be amplified using real time RT-PCR (reverse transcriptase – polymerase chain reaction) technology. Such amplification gives larger quantities of target sections of viral DNA which can accurately confirm the presence of virus.