M. catarrhalis usually resides in respiratory tract, but can gain access to the lower respiratory tract in patients with chronic chest disease or compromised host defenses, thus causing tracheobronchitis and pneumonia. For example, it causes a significant proportion of lower respiratory tract infections in elderly patients with COPD and chronic bronchitis.
M. catarrhalis commonly inhabits the respiratory system but can infiltrate the lower respiratory tract in patients suffering from persistent chest issues or compromised immune systems, resulting in tracheobronchitis and pneumonia. For example, it frequently contributes to significant lower respiratory infections among elderly individuals with COPD and chronic bronchitis.