Clinical Information

Respiratory infections are common and generally cause self-limited illnesses in healthy, immunocompetent hosts. Viruses account for a significant percentage of respiratory diseases, but bacteria may be associated with respiratory infections. Although respiratory illnesses are frequently mild, viruses may cause significant morbidity and mortality in immunocompromised hosts (eg, transplant recipients, patients with underlying malignancies).

Influenza viruses (type A and type B) and respiratory syncytial virus (RSV) are 2 common causes of viral respiratory illness, with peak incidence in the winter and spring months in the Northern hemisphere. Both viruses can cause a clinically indistinguishable syndrome, characterized by fever, cough, headache, and general malaise. RSV is a leading cause of respiratory illness in young children. Early diagnosis of influenza and RSV is important so that 1) necessary infection control precautions can be taken if the patient is hospitalized, and 2) antiviral therapy can be considered if the patient is hospitalized or considered at high-risk for severe disease.(1) Human metapneumovirus is also a cause of respiratory illness in both children and adults.

Human rhinovirus and coronavirus (serotypes HKU1, NL63, 229E, OC43) are the causative agents of the common cold, with symptoms including runny nose, sore throat, and malaise. Infections with rhinovirus and coronaviruses are extremely common, due to the large number of serotypes of these viruses. Most infections are mild and self-limiting; however, immunocompromised hosts may suffer more severe illnesses, including lower respiratory tract disease.

Parainfluenza viruses and adenovirus are also common causes of viral infection, especially in young children. Parainfluenza viruses are most common during the spring, summer, and fall months, with symptoms including fever, runny nose, and cough. However, parainfluenza viruses may also cause more severe lower respiratory disease, such as croup or pneumonia. Adenoviruses may infect a range of organ systems, with sequelae ranging from cold-like symptoms (sore throat), to pneumonia, conjunctivitis (pink eye), or diarrhea. Similarly to the viruses described above, parainfluenza viruses and adenoviruses generally cause mild, self-limited infections but may cause severe disease in immunosuppressed patients.

Respiratory infections may also be caused by bacterial pathogens, including Bordetella pertussis, Bordetella parapertussis, Chlamydophila pneumoniae, and Mycoplasmoides pneumoniae (previously Mycoplasma pneumoniae). Bordetella pertussis is the causative agent of pertussis, or whooping cough, a disease characterized by prolonged cough that may be associated with an inspiratory whoop and post-tussive vomiting. Bordetella parapertussis causes a similar, but generally less severe illness. Mycoplasmoides pneumoniae is a cause of upper respiratory infection, pharyngitis, tracheobronchitis, and pneumonia. Chlamydophila pneumoniae is a rare cause of pneumonia.