What is pneumonia and what typically causes it?

Pneumonia is defined as an infection that inflames the air sacs in one or both lungs, which may fill with fluid or pus, leading to cough with phlegm or pus, fever, chills, and difficulty breathing. The infection can be caused by various microorganisms, including bacteria, viruses, or fungi. This makes the option highlighting an infection caused by these agents the most accurate description of pneumonia.

Bacterial pneumonia is often caused by Streptococcus pneumoniae, while viral pneumonia can be caused by influenza virus or coronaviruses, among others. Fungal pneumonia, though less common, can occur in individuals with weakened immune systems or in certain geographic areas.

Understanding this helps establish the multifactorial nature of pneumonia, which can vary in terms of causative organisms based on factors such as the patient's age, health status, and local epidemiology. The other choices do not accurately depict pneumonia, as they either refer to conditions affecting other parts of the respiratory system or describe diseases that are not directly related to pneumonia's infectious nature.