Influenza
Influenza
Symptoms of flu
Infection with the flu virus usually starts abruptly with sweats and chills, muscular aches and pains in the limbs, dry sore throat, cough and high temperature. Someone with flu may be bed-bound and unable to go about usual activities, and this differentiates it from viruses causing a cold, which are not so severe. There is often a period of generalised weakness and malaise following the worst of the symptoms, which may last a week or more. A dry cough may also persist for some time.
Except during an epidemic, true seasonal flu is relatively uncommon compared with the large number of flu-like viral infections that can occur. However, when a flu outbreak happens, it can spread rapidly throughout a community.
Most cases can be managed by following simple advice. As with other viral coughs and colds (and Covid-19), for most people, there is nothing to be gained by taking antibiotics for flu, but antibiotics are often prescribed inappropriately ‘just in case’. Overuse of antibiotics should be avoided to reduce the development of bacteria that are resistant to them.
Advice on managing flu
- Drink adequate fluids to avoid dehydration
- Take paracetamol or ibuprofen for symptomatic relief
- Rest in bed if fatigued
- Stay off work or school if unwell. For most people, about one week will be adequate
- Fever and associated systemic symptoms of uncomplicated flu usually resolve after about one week, although some symptoms (such as cough and fatigue) may persist for several weeks after resolution of fever
- Follow-up is required if there is no improvement of significant illness after one week or deterioration
- Extra caution is required, with a low threshold for review, in a young child or baby with flu.
Seek urgent medical attention (see also Covid-19) if:
- Severe illness or ‘collapse’
- Shortness of breath or pleuritic chest pain
- Severe or productive cough; persisting high fever
- Delirium or confusion – particularly in the elderly
- Coughing up blood (haemoptysis).
Complications of flu
Damage caused to the airways by the virus means that flu can be complicated by secondary lung infection (pneumonia or pneumonitis). Such complications are much more likely to occur in young babies, who have not yet developed resistance, the very old and frail, who may have impaired immunological responses, and those who have pre-existing heart disease or respiratory disease (asthma or chronic obstructive pulmonary disease [COPD]), where further damage is more critical.
People with kidney disease, a weak immune system or diabetes are also at greater risk of pneumonia. Warning that pneumonia complications are developing may be given by a severe or productive cough, persisting high fever, pleuritic-type chest pain or delirium. If this is suspected, people with such symptoms need urgent referral for further assessment. In these cases, antibiotics may be needed.
Antivirals and seasonal flu
NICE supports the use of oseltamivir and zanamivir (neuraminidase inhibitors) in seasonal flu outbreaks for those who are in at-risk groups if treatment is started within 36 hours for zanamivir (and 48 hours for oseltamivir).
These drugs can also be used to prevent transmission of flu (prophylaxis) under some circumstances. Advice to use these drugs for prophylaxis is triggered if the incidence of flu hits a specific threshold. The incidence is monitored by a national surveillance scheme.
The effectiveness of antivirals during a pandemic cannot be known until used in such a situation and can only be guessed at based on experience in seasonal flu and in those infected with animal strains of flu. It is believed that these drugs may reduce the chance of developing complications and the chance of dying, and shorten the time taken to recover from an infection. They may reduce spread of flu virus. There is uncertainty as to how much resistance to antivirals could be present with their widespread use in the context of pandemic flu.