Causes of community-acquired pneumonia

Germs can reach the lower airways through breathed-in droplets or secretions, or after material from the mouth or stomach enters the lungs. The infection causes inflammation and fluid or mucus in the air sacs, making oxygen transfer harder. Bacteria are a common cause, while respiratory viruses such as influenza and COVID-19 can also cause pneumonia directly or make a secondary infection more likely. A person can develop pneumonia without knowing which germ is responsible.

Symptoms may include cough, fever, chills, shortness of breath, chest discomfort and tiredness. Some people cough up phlegm. Older adults or people with other illnesses may have confusion, weakness or a lower-than-expected temperature rather than a typical fever.

Arrange prompt medical assessment for a new cough with breathlessness, fever, chest pain or marked weakness. A clinician may listen to your lungs, check oxygen levels and decide whether imaging or other tests are needed. Treatment depends on the likely cause and severity; antibiotics help bacterial infections but do not treat viruses. Rest, fluids and fever relief may support recovery when suitable for you. Take prescribed medicine as directed and avoid smoking or vaping while your lungs are irritated.

Seek emergency help for severe difficulty breathing, blue or grey lips, new confusion, fainting, severe chest pain, or inability to stay awake. Urgent assessment is also needed when symptoms worsen quickly, dehydration prevents drinking, or a person with pneumonia becomes unusually cold, weak or confused, because a serious bloodstream response such as sepsis can develop.

Could this be pneumonia, influenza or COVID-19? Do I need an oxygen check, chest imaging or testing? What treatment is appropriate, and which changes mean I should return urgently?