Evaluation of saliva as diagnostic materials for influenza virus infection by PCR-based assays

Immunochromatographic antigen tests have been widely used for detection of influenza virus; however its low sensitivity restricts the use of clinical materials other than nasopharyngeal swabs. Saliva is obtained non-invasively and has utility for diagnosis of influenza. Polymerase chain reaction (PCR) is not typically used for rapid testing because it is time consuming. We evaluated the utility of saliva as diagnostic materials for influenza virus infection by PCR-based assays. Nasopharyngeal swabs and saliva were simultaneously collected from 144 patients and investigated by reverse transcription-quantitative PCR (RT-qPCR) and droplet-RT-PCR. Overall concordance of results from nasopharyngeal swabs and saliva were 95.8%. Influenza gene was detectable in less than 12min in saliva by the droplet-RT-PCR. Saliva as well as nasopharyngeal swabs contained more than 1×102 copies/μl of the influenza gene. About half of the patients provided positive results in nasopharyngeal swabs and saliva within 24h from the onset of the symptoms. The study demonstrates that saliva can be used as an alternative specimen source to nasopharyngeal swabs. When rapid PCR assay including RNA extraction to be full-automation in a miniaturized machine, point-of-care test based on PCR may be realized using saliva without restriction of materials. •High degree of result concordance was obtained from nasopharyngeal swabs and saliva.•The droplet-RT-PCR assay could amplify influenza gene in the saliva within 14min.•Saliva contained influenza gene more than 1×102 copies/μl of influenza gene.•About 50% of saliva was positive within 24h after the onset of symptoms.