Interferon Reference for Older People - REFIPA Study

The diagnosis of respiratory viral infections is mainly based on PCR tests targeting the DNA or RNA of suspected viruses, including SARS-CoV-2, RSV and influenza viruses. However, this method is limited because it only tests for a small number of viruses, while many other pathogens can cause similar symptoms. As a result, respiratory viral infections are often underdiagnosed because not all possible viruses are systematically tested for. Another limitation of PCR tests is that they can detect residual viral genetic material long after the infection has ended, making it difficult to distinguish between an active infection and a past one. Viral load can help interpret the result, but it is not always reliable. It is therefore essential to have complementary markers that can indicate whether the detected virus is still in the active replication phase. An innovative approach is to measure the host's immune response, in particular the production of type I interferons (IFN-I), which are markers of active viral infection. Studies have shown that joint analysis of the IFN-I/III response and PCR tests improves the detection of viral respiratory infections by better discriminating between active infections. This method shows promise for refining diagnosis, particularly in cases where the viral load is low or ambiguous. These advances are particularly important for older patients, in whom viral infections have a severe impact. Ageing leads to a decline in immune function (immunosenescence), including a reduction in IFN-I production. This alteration could further complicate the interpretation of immune biomarkers in older people, highlighting the need to establish reference values specific to this population. In this context, the RESPIGERIA study (compliance with MR004 No. 24-5127) was launched to evaluate the IFN response in geriatric hospitalised patients with respiratory viral infections. However, there is still a lack of reference data on the IFN response in uninfected