Pneumonia is an inflammatory condition of the lower respiratory tract affecting the lung’s functional tissue (parenchyma), namely the alveoli and bronchioles. The air sacs get swollen and fill with pus (microorganisms, inflammatory response cells and other fluids) hindering oxygen exchange and making it harder to breathe.^1,2,3,4

Recovery typically takes 2-4 weeks, but the risk of getting seriously ill is higher with infants, older people, and those with heart or lung conditions.¹

The most usual cause is bacterial infection, but viral causes are also common. Fungal pneumonia and aspirational pneumonia (involving aspirated food, drink, or vomit or an inhaled foreign object) are less common. Chemical or smoke inhalation can also increase the risk of infection due to cellular injury. Rarer types of pneumonia can arise from over-sensitive immune reactions.^2,5,6

Most pneumonia develops outside of hospital or healthcare settings and is called community acquired pneumonia or CAP. Hospital-acquired pneumonia (HAP) is defined as pneumonia that occurs 48 hours or more after a patient has been admitted to hospital and the pneumonia was not incubating in the person when admitted. Ventilator associated pneumonia is a risk due to intubation associated with intensive care.³

‘Double pneumonia’, referring to pneumonia in both lungs (bilateral pneumonia), is a term particularly used in North America.⁷