Infections of the respiratory tract are mainly caused by viruses (e.g. influenza viruses, adenoviruses, RSV), but also bacteria (e.g. Legionella, Bordetella pertussis, Mycoplasma pneumoniae, Chlamydia pneumoniae). Both the upper (e.g. nasal mucosa, paranasal sinuses) and the lower respiratory tracts (airways and bronchia) can be affected. The pathogens are mainly transmitted by droplet infection. Symptoms of respiratory infections include fever, cough, headaches and pain, pharyngitis, sinusitis, bronchitis or pneumonia.
Since many respiratory pathogens cause similar symptoms, the diseases cannot usually be diagnosed based on the clinical image alone. Consequently, laboratory diagnostics are particular valuable. Direct pathogen detection (e.g. PCR) is in most cases the method of choice for the detection of acute respiratory infections.
Since antibodies are only formed some days or weeks following infection and the prevalence increases with age, an infection can often only be diagnosed retrospectively by investigation of a serum pair and detection of an IgG titer increase. Serological tests can also contribute to epidemiological monitoring.