COVID-19 became one of the most devastating pandemics in human history. As in all pandemic diseases rapid diagnosis of people carrying the infectious agent and their quarantine before they transmit the disease to healthy people is the key measure to control the disease in large populations . Currently, PCR is the main diagnostic tool for rapid and sensitive diagnosis of COVID-19 [3, 4].
The gold standard test for detecting SARS-CoV-2 is considered to be the analysis by RT-PCR of a sample obtained by nasopharyngeal swab. Therefore, the most widely used application for obtaining samples for PCR is by a nasopharyngeal swab. However, besides being very discomforting, many adverse effects associated with nasopharyngeal swab sampling, including epistaxis in 8.3% of cases, have been reported. Additionally, nasopharyngeal swab sampling poses an important risk of transmission of the virus to healthcare personnel who have to do tens to hundreds of sampling every day, in centers with high admission rate [5,6,7].
It is expected to find SARS-CoV-2 in the oral secretions of COVID-19 patients. Epithelial cells in the oral cavity have been shown to express large amount of ACE2 receptors, which plays a key role in the entry and replication of SARS-CoV-2 . Nasopharynx and oropharynx are not separated from each other physically and it is logical to think that the secretions in the nasopharynx will be mixed into the oral secretions. Additionally, virus particles in the blood may pass into exudates produced in the oral cavity.
Several studies revealed the presence of SARS-CoV-2 in saliva of COVID-19 patients. The sensitivity of RT-PCR analysis of saliva specimens was 66% to 92% for COVID-19 as compared with the standard diagnosis with nasopharyngeal swabs [9,10]. In this study, we have shown that SARS-CoV-2 RNA is pretty stable in oral secretions if it is stored at room temperature. There was not any loss of viral RNA after storing the mouthwash samples for 3 days at room temperature and only ten-fold decrease at the end of 10 days. Storing at 4°C preserved the viral RNA as well as room temperature but it did not improve the quantity of viral RNA that can be detected by RT-PCR. Inspired by these data we investigated the possibility of using concentrated gargle and mouthwash samples instead of nasopharyngeal swab samples with the same or better efficiency in the diagnosis of COVID-19.
Recently, we have developed a method for concentrating biological fluids by the help of elastic polymer meshes that absorb water and other molecules and thus concentrate microorganisms and macromolecules. In a recent study we have shown that, by this method, it was possible to increase the sensitivity of antigen tests detecting tuberculosis antigens in urine samples of tuberculosis patients (unpublished internal data). In this study we have evaluated the efficiency of MyMagiCon–RW100®, which is intended for concentrating gargle and mouthwash.
The results of this study showed that gargle and mouthwash samples can be used as efficiently as nasopharyngeal swab samples, after concentrating by MyMagiCon–RW100®. Among all 114 patients in whom SARS-CoV-2 RNA was identified by RT-PCR in at least one of the nasopharyngeal or gargle and mouthwash samples, 76 (%66.7) was identified in nasopharyngeal swab and 67 (%58.8) in gargle and mouthwash samples. However, when gargle and mouthwash samples were concentrated by MyMagiCon–RW100®, it was possible to identify SARS-CoV-2 RNA in 101 (%88.6) of samples making them better samples than nasopharyngeal samples for the diagnosis of COVID-19. An interesting finding was the presence of SARS-CoV-2 RNA in only nasopharyngeal samples of 10 patients and in only concentrated gargle and mouthwash samples of 35 patients. If the virus was really present in only nasopharyngeal or oropharyngeal cavity at the time of sampling, or there was a problem with collecting the samples properly, needs further investigation.
Using gargle and mouthwash samples instead of nasopharyngeal swab samples will increase the patient compliance, eliminate the adverse effects of nasopharyngeal swab sampling, significantly decrease the infection risk of health personnel obtaining the samples and prominently lower the workload of healthcare centers. When the rapid antigen tests with sensitivities close to RT-PCR become available, MyMagiCon–RW100® may enable rapid diagnosis from mouthwash samples which may be applied in hospitals or even at homes for self-testing.