Our group is involved in the field of clinical virology with special focus on respiratory viruses and viral infections in immunocompromised hosts. We have investigated the role of respiratory viruses in different populations, but we have been particularly interested in immunocompromised hosts hospitalized with lower respiratory tract infections. In the community we have also analyzed the relations between influenza, antivirals, and antibiotic overuse. In order to better understand the impact of respiratory viruses we have developed and validated a large panel of tests aiming to identify respiratory viruses that commonly infect humans (real-time PCR, culture, serology, antigen detection, culture). These tests need to overcome the wide diversity of the different subtypes and serotypes causing diseases and we have carefully investigated the variability of respiratory viruses circulating in the community, particularly rhinovirus and influenza (by sequencing circulating strains and by hemagglutination inhibition assays). Our group functions as a reference laboratory for influenza and SARS surveillance in Switzerland in close collaboration with the Swiss Federal Office of Public Health and WHO (www.influenza.ch) and is involved in the surveillance of emerging viruses. Our research activities include also cytomegalovirus infections in transplant recipients. By developing ultrasensitive assays we have been able to better describe the kinetic of CMV replication in transplant recipients.