What can cause pneumonia?

Infectious pneumonia may follow bacteria or viruses such as those responsible for influenza or COVID-19; less commonly, fungi are involved. Aspiration pneumonia develops when saliva, food, stomach contents, or liquid enters the airways and reaches the lungs. The cause is not always identified from symptoms alone. A clinician may use the history, examination, chest imaging, and selected tests to guide treatment. Pneumonia is different from sepsis, although a serious lung infection can sometimes lead to that whole-body response.

Seek medical advice for a new cough with fever, breathlessness, chest discomfort, or marked fatigue. Mention recent viral illness, swallowing difficulty, vomiting, dental problems, travel, immune-system conditions, and medicines. These details can change which causes are considered. Do not start leftover antibiotics, because they do not treat viral or fungal causes and may delay the right care. Follow the prescribed plan and maintain fluids if suitable for you.

Get urgent help for severe breathing difficulty, blue or grey lips, confusion, fainting, coughing blood, chest pain, or inability to drink. After possible aspiration, urgent assessment is especially appropriate if coughing and breathlessness begin suddenly or worsen. A deteriorating general condition can indicate a complication and should not be judged by the suspected cause alone.

Ask which cause is most plausible, whether testing is useful, whether aspiration is a concern, how treatment will target the suspected cause, and how to prevent another episode.