Assessing the role of saliva and gargle lavage as a cost-effective alternative to the throat and nasal swabs for diagnosing Covid-19

Abstract

Background: Presently, the most reliable and common method for definitive diagnosis of COVID-19 is the use of nasal swabs and throat swabs (NTS) by RT-PCR (reverse transcription-polymerase chain reaction). Limited use and efficacy of other sampling methods like gargle lavage have been seen clinically owing to the non-availability of gargle liquid. Aims: The present study was conducted to assess and evaluate the SARS-CoV-2 RNA stability at 4o C in the normal saline as a transport medium and gargle liquid. The present study also assessed the agreement of saliva/gargle liquid and nasal swabs and throat swabs in detecting SARS-CoV-2. Methods: In 30 subjects who had confirmed positive real-time RT-PCR (RT-PCR) positive diagnosis for COVID-19, paired samples of saliva, gargles, and NTS were acquired. For detection of SARS-CoV-2 RNA stability in the normal saline, the collected gargle lavage samples were divided into two aliquots where one sample was processed after 24-30 hours after storing at 4o C, whereas, another sample was processed with routine saliva and NTS sample within 4-6 hours. The agreement was assessed between cycle threshold (Ct) values for the two aliquots using statistical analysis. Results: Negative saliva samples were seen in 6.66% (n=2) subjects with positive NTS and 13.33% (n=4) subjects with negative NTS. A positive saliva sample was seen in 73.33% (n=22) subjects with positive NTS and 6.66% (n=2) subjects with negative NTS. Concerning the comparison of gargle lavage samples processed after 24-30 hours, there was a 3.33% (n=1) negative sample for NTS positive and 16.66% (n=5) for NTS negative. There were 80% (n=24) gargle lavage positive samples for NTS positive and no positive sample for NTS negative. There was total 83.33% (n=25) gargle lavage positive samples and 16.66% (n=5) gargle lavage samples negative samples. For gargle lavage samples processed immediately, there were 3.33% (n=1) negative samples that were positive for NTS and 13.33% (n=4) samples that were positive for NTS. Conclusions: The present study concludes that SARS-CoV-2 RNA remains stable in the gargle samples stored in the normal saline for nearly 24-30 hours. Saliva and gargle lavage serves as acceptable and cost-effective sampling methods for detecting SARS-CoV-2 RNA using RT-PCR. These methods are also acceptable, inexpensive, and simplified methods of collecting samples reducing expenses and workload on the healthcare professionals concerning the sample collection.