Saliva as a Reliable and Non-Invasive Sample for Detecting Influenza A in Severe Acute Respiratory Infection Cases

Nasopharyngeal swab sampling remains the gold standard for influenza A diagnosis but has limitations, such as dependence on medical staff, invasiveness, nosocomial transmission, and occupational exposure risk. This study aimed to investigate whether saliva and nasal vestibular swabs are suitable non-invasive alternatives to nasopharyngeal swabs for influenza A detection in severe acute respiratory infection (SARI) cases. Paired saliva and nasal vestibular swabs were collected on the same day from 16 cases diagnosed with influenza. Saliva samples demonstrated a higher sensitivity (87.5%) than did nasal vestibular swabs (31.3%) in RT-qPCR, when compared with the diagnostic results obtained from nasopharyngeal swabs. While nasal vestibular swabs showed inconsistent results, saliva samples consistently tested positive, particularly within 7 days of symptom onset (100% positive agreement). In addition, diagnosis with RT-qPCR is often delayed because it requires trained laboratory technicians and facilities with appropriate laboratory settings. Therefore, the GenPad®, a rapid diagnostic device, was evaluated using saliva samples and showed promising performance (92.9%) compared with the efficiency of RT-qPCR. Factors such as the location of infection (upper vs. lower respiratory tract infections), sample collection timing, pre-collection instructions, and nucleic acid extraction possibly contributed to the detection efficiency. Despite the small sample size and lack of influenza-negative controls, our findings support saliva as a viable self-collected sample for influenza A diagnosis and surveillance programs. Non-invasive sampling mitigates discomfort, minimizes infection risk for healthcare workers, and improves testing capacity, particularly under frequent staff shortages during pandemics.