Assessment of the Type I IFN Response in the Nasal Cavity During Respiratory Viral Infections in a Geriatric Department

The diagnosis of respiratory viral infections is usually based on testing for pathogens suspected of causing the infection using PCR tests that target the pathogens' DNA or RNA. A specific PCR test is required for each pathogen. In most cases, testing is carried out primarily for three specific viruses (SARS-CoV-2, respiratory syncytial virus (RSV), influenza virus) is carried out as a first-line test. However, numerous viruses can cause these infections (adenovirus, metapneumovirus, rhinovirus, parainfluenza virus, bocavirus, etc.). Consequently, performing a specific PCR test for every virus that could cause respiratory symptoms is not feasible, and viral infections are often under-diagnosed because the screening for viruses is not exhaustive. To address this issue, analysing the host response to determine the microbial aetiology of an infection may represent an innovative alternative for the diagnosis of infections. A common feature of all viruses is their ability to induce type I interferons (IFN-I). Thus, measuring this IFN-I response could help direct the diagnosis of respiratory infections towards a viral origin. Furthermore, the detection of a virus via PCR in a respiratory sample may indicate an active or recent infection, but may also be detected following an infection that occurred several weeks or months earlier. The viral load in the sample is an important factor in distinguishing between these two scenarios but does not always allow for a definitive conclusion (some patients may have low viral loads whilst still having an active infection). It is therefore sometimes difficult to distinguish, using a PCR test that detects the viral genome, between the virus currently replicating and traces of viral genetic material from dead viruses. It is therefore necessary to have markers that can be associated with an active/replicating infection to aid interpretation in the event of a positive PCR result. Using nasopharyngeal swabs collected for the diagnosis of