What characterizes a respiratory infection?

A respiratory infection is characterized specifically by its effect on the airways and lungs. This includes infections that can be caused by various pathogens such as viruses, bacteria, or, less commonly, fungi, which directly impact the structures involved in the respiratory process – for example, the nasal passages, pharynx, larynx, trachea, bronchi, and lungs. Common examples of respiratory infections include the common cold, influenza, pneumonia, and bronchitis.

In contrast, an infection of the digestive system pertains to a completely different area of the body—most commonly impacting the gastrointestinal tract—therefore, it doesn't relate to respiratory infections. Similarly, a skin infection affects the dermal layers of the body and does not involve the respiratory system. Lastly, while fungi can be a cause of certain respiratory infections, stating that infections are solely caused by fungi excludes bacterial and viral infections, which are far more common in respiratory conditions. Therefore, the correct answer focuses on the primary anatomical areas impacted by the infection.