What is influenza?
Influenza, or flu, is an infection of the nose, throat and lungs caused by influenza viruses. It spreads easily through droplets from coughs and sneezes and from contaminated hands. In India, flu tends to rise during the monsoon and again in winter, though cases occur all year. Strains such as H1N1 and H3N2 are types of seasonal flu.
Flu is different from the common cold. It comes on suddenly and makes people feel much more unwell, often unable to go to work or school for several days. The virus changes a little every year, which is why people can catch flu more than once.
Symptoms of flu
Symptoms usually begin one to four days after catching the virus. Most healthy adults recover within a week, though tiredness and cough can last two weeks or more. Older people may have fewer typical symptoms and may simply feel very weak or confused.
- Sudden high fever and chills
- Severe body ache and headache
- Extreme tiredness and weakness
- Dry cough and sore throat
- Runny or blocked nose
- Sometimes vomiting or loose motions, especially in children
Who is at higher risk?
Some people are more likely to develop complications like pneumonia. These include adults over 65, children under five, pregnant women, and people with diabetes, asthma, heart disease, kidney or liver disease, or weak immunity. People in these groups should see a doctor early when flu symptoms start, as early treatment can reduce the risk of serious illness.
How influenza is diagnosed
Doctors usually diagnose flu from the symptoms, especially during flu season. A nose or throat swab test can confirm influenza when the result will change treatment, such as in high-risk patients or those admitted to hospital. The RT-PCR test is the most accurate; rapid antigen tests give faster results but can miss some cases.
Blood tests and a chest X-ray may be needed if pneumonia or another infection is suspected. Because dengue and other monsoon fevers can look like flu at first, your doctor may also order tests to rule them out. A pulse oximeter reading can help show whether the lungs are affected.
Treatment and home care
Most people get better with rest, plenty of fluids and light meals. Paracetamol helps with fever and body ache; follow the label or your pharmacist's advice. Stay at home until you have been fever-free for at least a day, to avoid spreading the virus.
Antiviral medicines such as oseltamivir can shorten illness and lower the risk of complications, especially when started early. These are used only on a doctor's prescription, usually for high-risk or very unwell patients. Antibiotics do not work on the flu virus and are used only if a doctor finds a bacterial complication.
Possible complications
Most people recover fully, but flu can sometimes lead to pneumonia, either from the virus itself or a bacterial infection that follows. It can also worsen existing asthma, heart failure or diabetes, and in rare cases affect the heart or brain. Complications are more likely in the high-risk groups described above.
A warning pattern is when fever and cough seem to be improving and then suddenly get worse, with new breathlessness or chest pain. This needs a doctor the same day. People with diabetes should check their blood sugar more often during flu, as illness can push sugar levels up.
Prevention and the flu vaccine
A flu vaccine once a year is the best way to reduce the risk of flu and its complications. The vaccine is updated each year to match the strains expected to circulate. It is especially recommended for pregnant women, older adults, young children, healthcare workers and people with long-term illnesses.
Simple habits also help: wash hands often, cover coughs and sneezes with a tissue or elbow, wear a mask when unwell or in crowded places during outbreaks, and avoid close contact with sick people. If someone at home has flu, keep their towels and utensils separate and open windows for fresh air.
When to see a doctor for influenza
See a doctor early if you belong to a high-risk group, or if symptoms are severe or not improving after a few days. Seek urgent care for any warning signs below. Talk to your doctor or pharmacist about the flu vaccine and which medicines are safe for you.
Medicines doctors commonly use
Only your doctor can decide which medicine, dose and combination is right for you.
- Paracetamol (fever and pain reliever)Relieves fever, headache and body ache.Follow the label or your pharmacist's advice; do not exceed the stated amount.
- Antiviral medicines such as oseltamivirReduce the flu virus's ability to multiply and can shorten illness if started early.Only on a doctor's prescription, mainly for high-risk or severely ill patients.
- Influenza vaccine (yearly)Trains the immune system to protect against expected flu strains.Given once a year; tell the doctor about any past severe vaccine reaction.
- Oral rehydration solution (ORS)Replaces fluids and salts lost through fever, sweating or loose motions.Prepare exactly as directed on the packet.
See a doctor urgently if
- Difficulty breathing, fast breathing or chest pain
- Bluish lips or face, or low oxygen reading on a pulse oximeter
- Confusion, severe drowsiness or a fit (seizure)
- Fever that improves and then returns with a worse cough
- Not passing urine, severe weakness or unable to keep fluids down
- Any flu symptoms in pregnancy, infants or people with long-term illness
Tests that may help
This article is general health information, not medical advice. Do not start, stop or combine medicines on your own — always follow your doctor's prescription and ask your pharmacist if unsure.