ABSTRACT
Upper and lower respiratory tract infections are the most common infections among all age-groups. Lower respiratory infections including acute bronchitis, bronchiolitis, pneumonia, and tracheitis are more severe than upper respiratory infections such as the common cold, laryngitis, pharyngitis/tonsillitis, acute rhinitis, acute rhinosinusitis, and acute otitis media. The main causative agents of severe lower respiratory illness are bacteria such as Streptococcus pneumoniae and Haemophilus influenzae with more capability to cause upper and lower respiratory tract infections. Other pathogens accountable for respiratory infections including human rhinoviruses, respiratory syncytial virus, adenoviruses, enteroviruses, human parainfluenza viruses, human metapneumovirus, and human coronaviruses are associated with the development of acute respiratory infections. As per the WHO report, about 290,000–650,000 deaths per year are caused by influenza virus infections alone. Acute respiratory infections cause a considerable rate of death and morbidity globally. Nevertheless, due to the symptom similarity between these infections and the asymptomatic state of infection, it’s quite challenging to identify the main cause without laboratory testing. This chapter presents epidemiological data, types of respiratory infections, and their respective mode of transmission. Additionally, occurrence and transmission potential of symptomatic, asymptomatic, and respiratory co-infections are discussed.
