What should you know about influenza caused by which virus?

Influenza viruses change over time, so circulating strains can differ from one season to another. Influenza A infects people and some animals; influenza B mainly circulates among people. Both can cause a sudden illness with fever, cough, chills, headache, fatigue and a general feeling of being unwell. Symptoms overlap with other respiratory infections, so symptoms alone cannot identify the virus or confirm influenza. Pneumonia can develop as a complication or occur from a different infection.

Rest, drink enough fluid to keep your urine pale, and limit close contact while you are feverish or acutely unwell. Cover coughs and sneezes, wash hands and improve ventilation indoors. A clinician may recommend testing or antiviral treatment according to your symptoms, timing and health risks. Do not start antibiotics without advice; antibiotics do not treat viruses. Follow the directions on any medicine and check combination products for repeated ingredients.

Seek urgent care for breathing difficulty, chest pain, confusion, fainting, severe dehydration, or a sudden deterioration. Arrange medical advice for a fever that persists, worsening cough, unusual drowsiness, or symptoms that improve and then return more severely. Seek earlier advice if you are pregnant, have a long-term illness, or have reduced immunity.

Ask whether testing can distinguish influenza from another infection, whether antiviral medicine is appropriate, and how to protect people at home.