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Clinical features

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

For healthy individuals the infection is an unpleasant but usually self-limiting disease and patients usually recover within 2–7 days.

Serological studies have revealed that around 30 to 50% of influenza infections can be asymptomatic, however, this may vary depending on the characteristics of the influenza strain (1).

In mild, uncomplicated influenza, after an incubation period of between one and four days, there is an abrupt onset of:

fever – usually it ranges between 38–40°C, the peak occurs within 24 hours of onset and lasts for 3 days
malaise
headache
chills
cough – generally dry but may be productive in some cases
myalgia – mainly the back and the limbs
extreme fatigue
nasal congestion
sore throat
anorexia
gastrointestinal symptoms – such as vomiting and diarrhoea are uncommon (10%) in adults (1,2)

Symptoms may vary in infants and children and may include fatigue, irritability, diarrhoea and vomiting (3).

After three to seven days the fever ceases and illness typically resolves although cough, malaise and lassitude may persist for a longer period (2).

Although the infection is usually self limiting it may cause complications such as primary influenza viral pneumonia, exacerbation of underlying medical conditions (e.g., pulmonary or cardiac diseases) and co-infections with other viral or bacterial pathogens (4).

Reference:

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