Symptoms of flu

 Some, or all, of these symptoms of uncomplicated influenza may be present:

•    A high fever (often higher than 39°C) with chills. The fever is highest in children and least marked in the elderly.
•    Dry cough
•    Sore throat
•    Blocked nose or nasal discharge
•    Sweating and shivering
•    Muscle aches and pains, especially in the legs (the “I've been run over by a bus” feeling)
•    A general feeling of unwellness
•    Fatigue and wanting to sleep all day

Symptoms can occur abruptly, and it is sometimes possible to pinpoint the exact hour of the day that symptoms began. Children often vomit and have diarrhoea, but these symptoms are infrequent in adults. In addition, flu complications may occur.


Both children and adults can develop serious complications when they have flu. These include:

Primary influenza virus pneumonia

This form of pneumonia occurs when the flu virus has caused severe lung damage. You’ll start with the usual symptoms of flu, but the fever will persist, your cough will worsen and you’ll become extremely short of breath. In severe cases, you may have a bluish tinge and become confused due to a lack of oxygen.

This form of pneumonia is very serious and will require intensive respiratory support in a hospital. Most people who develop primary viral pneumonia have underlying heart and lung disease and should therefore have a yearly flu vaccination.

Secondary bacterial pneumonia

This is more common than viral pneumonia and occurs when bacteria cause a secondary infection in the lungs. Typical symptoms include recurrence of fever, shortness of breath and productive cough (when secretions come up during coughing) four to 14 days after the symptoms have almost disappeared.

This complication is most often caused by bacteria called Streptococcus pneumonia, Staphylococcus aureus and Haemophilus influenzae type B.

Some doctors recommend that people in high-risk groups be vaccinated against pneumococcal pneumonia as well as influenza.

Exacerbations of chronic lung diseases

It is well known that infection with viruses called rhinoviruses and coronaviruses may worsen chronic lung diseases – such as chronic obstructive pulmonary disease (COPD) – but influenza virus infection may be responsible for up to 25% of these exacerbations.

Otitis media and croup (in children)

As every mother knows, young children are prone to middle ear infections (otitis media) whenever they have an upper respiratory tract infection. In the majority of cases the ear infection is caused by the virus itself and is not a secondary bacterial infection, so antibiotics are seldom necessary.

Children may also develop croup (a viral infection of the vocal cords and large main airways) as a result of flu and other respiratory-tract virus infections.

Myositis and myocarditis

In rare cases inflammation of the muscles of the body (myositis) can occur. It’s more common in children and painful tender leg muscles are a symptom.

Also very rarely, the heart muscle may become inflamed (myocarditis). Symptoms include tiredness, shortness of breath, heart palpitations, a rapid pulse and discomfort in the chest.

Because myositis and myocarditis are more likely if the muscles are put under stress, it’s not a good idea to exercise while you have the flu (or any other viral illness).

Complications of the nervous system and brain

Young children with flu may have fever fits (called febrile convulsions), as is possible in any illness involving a high temperature.
Children with fever should never be given aspirin or medication containing aspirin. It is associated with a potentially fatal disease called Reye’s syndrome. Although the causes of Reye’s syndrome are unknown, it is almost exclusively seen in children who have been given aspirin to treat fever associated with virus infections.

Reye’s syndrome is a very serious condition affecting the brain and liver. Symptoms may include vomiting, lethargy, altered consciousness, seizures and respiratory arrest. The majority of children will recover from Reye’s syndrome, but in some cases permanent brain damage and death might follow.

Other central nervous system complications that have been associated with influenza virus infection include Guillain-Barré syndrome, encephalitis and transverse myelitis, but these are very rare.

It is impossible to accurately determine the true number of influenza infections, as many infections are not reported to healthcare institutions. In the United States, an estimated 5 to 20% of the population are annually infected with influenza viruses,which translates to 50 million cases. Worldwide, between 3 and 5 million cases of severe illness occurs, with an estimated 250 000 to 500 000 influenza-related deaths. About 21 percent of people living in the same house as an infected child or adult will contract flu, according to American studies.


Symptoms start about 48 hours after exposure to the virus, although this period may vary from one to four days. You typically have continuous fever for about three days, although other symptoms such as cough, lethargy and a general feeling of unwellness may persist for longer.

You’re considered “infectious” when the virus is shed from your airways. This can occur from the day of infection and can continue for eight days – even longer in people with decreased immunity. Most people have an uneventful recovery after treatment for symptoms only.

When should you see a doctor?

Under certain circumstances, you may need to consult your doctor when you have flu.

•    If you have a high fever for more than a few hours that does not respond to over-the-counter medicine, and you are not certain whether it is due to flu, it’s a good idea to see a healthcare professional for an opinion.
•    If your fever lasts longer than two days.
•    If you feel sick and just don't seem to get better.
•    If you have a cough that begins to produce phlegm.
•    Any sign of complications of flu should prompt a visit to a healthcare professional.
•    If you have difficulty breathing or feel a sharp pain when breathing.
•    If you fall into any of the high-risk categories recommended for vaccination, even a mild bout of flu should be treated by a health professional. This includes people with cancer, people on medication after organ transplantation and HIV-positive people.

How does a doctor diagnose flu?

Healthcare professionals can usually recognise flu by looking at the symptoms and signs alone.

Symptoms such as a high fever, a dry cough, nasal congestion and aching limbs make the diagnosis of flu very apparent. If it is known that flu is active in the community, then the diagnosis of flu becomes even more probable. The doctor’s suspicion can also be confirmed by a laboratory test.

The when and how of laboratory tests

Laboratory diagnosis of a viral respiratory illness might be attempted for one of the following reasons:

•    When the illness is severe, requiring admission to hospital
•    In children, where other viruses mimicking influenza may be the cause of disease
•    When infection with more than one virus is suspected
•    To help decide whether an antibiotic is necessary, because viral infections don’t respond to antibiotics
•    For academic interest

How is a laboratory test performed?

See above.

How can a doctor treat flu?

•    In low-risk cases and without signs of secondary bacterial infections, the doctor will treat the flu symptoms in very much the same way you would treat yourself: mainly with over-the-counter medications. When the diagnosis is clear and illness is uncomplicated, there is not much else to be done. Studies have shown that in the majority of cases the symptoms of flu will subside within three to four days with or without symptom-relieving medication.
•    Over-the-counter cold and flu preparations cannot cure flu, but will relieve symptoms.
•    In high-risk cases, antiviral drugs may be prescribed, or in people with a secondary bacterial infection appropriate antibiotics may be prescribed. Remember to complete all courses of prescribed antiviral drugs or antibiotics – this will prevent the development of resistant infections.
•    In more severe cases, the doctor might consider hospitalisation of the patient.

(Reviewed by Dr Jane Yeats, Department of Virology, University of Cape Town 2006)

(Updated and reviewed by Dr Jean Maritz and Dr Leana Maree, medical virologists, Tygerberg Hospital and University of Stellenbosch 2010)


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