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Ten tips on complications of seasonal and pandemic flu

With the nation braced for a swine flu epidemic either now or in the autumn, respiratory physicians Dr Thomas Bewick and Dr Wei Shen Lim provide a timely reminder of the complications of influenza

With the nation braced for a swine flu epidemic either now or in the autumn, respiratory physicians Dr Thomas Bewick and Dr Wei Shen Lim provide a timely reminder of the complications of influenza

1 Seasonal influenza usually resolves in about a week. The infection runs an uncomplicated course in most patients. Fever is the paramount symptom and typically lasts three days. In uncomplicated infection, the illness usually resolves within seven days, although cough, malaise and lassitude may persist for longer. In seasonal influenza, vomiting and diarrhoea are common in children under two years of age, but not in adults.

2 Secondary bacterial pneumonia is the most common complication of influenza. The most common pathogens are Streptococcus pneumoniae, Staphylococcus aureus and Haemophilus influenzae. GPs should suspect pneumonia if patients complain of increasing breathlessness at rest, or if they fail to improve within four to five days of symptom onset or within 48 hours of starting an antiviral agent. A productive cough may occur in uncomplicated infection – especially in patients with chronic lung disease – and therefore does not itself necessarily indicate a secondary bacterial infection.

3 Primary viral pneumonia can cause rapid deterioration and respiratory failure. This is much less common, but it has a mortality in hospitalised patients of up to 40%. These patients are likely to have bilateral predominantly mid-zone infiltrates on chest X-ray. Any patient with influenza who is more breathless than usual and has bilateral chest signs should be considered for referral to hospital for further evaluation.

4 The severity of pneumonia in adults may be assessed using the CRB-65 score. This score (confusion, respiratory rate 30/min or above, systolic blood pressure under 90mmHg or diastolic 60mmHg or below, age over 65) is well validated for use in community-acquired pneumonia, and can be used to assess the severity of influenza-related pneumonia. Patients scoring 1 or 2 may warrant referral to hospital for assessment, with those scoring 3 or 4 usually requiring urgent admission. The CRB-65 score does not replace clinical judgment. In the event of a pandemic, thresholds for hospital admission may vary depending on available resources. The CRB-65 score can be downloaded at

5 During a pandemic, patients should be offered appropriate antibiotics if the clinician suspects influenza-related pneumonia. The antibiotic of choice should cover the three most likely pathogens. For example, a seven-day course of doxycycline or co-amoxiclav is usually appropriate. A macrolide – such as erythromycin or clarithromycin – can be used as an alternative. Children should be considered for treatment with co-amoxiclav if they have comorbidity, severe disease, vomiting, drowsiness or severe earache. Patients with uncomplicated influenza should not be offered antibiotics at first consultation.

6 Influenza can cause a sudden deterioration in patients with significant comorbidities. Both adults and children with significant comorbidity are at increased risk of complications, death or hospitalisation if they contract influenza. This group of patients includes those with chronic lung, heart, liver or kidney disease, malignancy, immunosuppression and diabetes. Many of these patient groups are currently identified by the Department of Health for the annual influenza vaccine. Patients with severe comorbidity presenting with influenza-related exacerbations should be treated according to disease-specific guidelines.

7 Children are at increased risk of developing otitis media, croup, febrile convulsions and bronchiolitis. Otitis media is the most common bacterial additional infection, complicating influenza in up to 25% of children. Croup caused by influenza tends to be more severe than that caused by parainfluenza, and is more often complicated by bacterial tracheitis. Influenza is the second most common cause of bronchiolitis after respiratory syncytial virus, and is similar in clinical presentation. Febrile convulsions tend to occur at the onset of fever (in contrast to seizures described with encephalitis), and may be recurrent.

8 Children with signs of respiratory distress should be referred to hospital for assessment. Signs of respiratory distress include a markedly increased respiratory rate, grunting, intercostal recession or breathlessness with chest signs. Other indicators of severe disease are cyanosis, severe dehydration, altered conscious level, complicated or prolonged seizures, or signs of sepsis (extreme pallor, hypotension or a floppy infant).

9 Myalgia is common, myositis less so. Myalgia is one of the most common presenting features associated with uncomplicated influenza, usually affecting the neck, back and limbs. However, myositis associated with a rise in creatine kinase levels, particularly of soleus and gastrocnemius, has been described. This most commonly occurs in children, after upper respiratory symptoms have subsided. Myositis is usually mild and self-limiting, and only rarely associated with myoglobinuria and renal failure.

10 Encephalopathy and encephalitis are rare complications of influenza infection. Neurological complications have been most widely reported in children, mainly in Japan. Encephalopathy is characterised by altered conscious level and seizures, on average three days after onset of the illness. The clinical course is severe, with a mortality of 31%, persistent neurological deficit in 26% and full recovery in 43%. Reye's syndrome is a rare childhood acute encephalopathy with raised liver enzymes.

A causal link with influenza has not been proven, but this condition is associated with influenza activity and aspirin use. Aspirin is contraindicated in children (less than 16 years old) with influenza infection.

Dr Thomas Bewick is clinical fellow in respiratory infection and Dr Wei Shen Lim is consultant in general and respiratory medicine at Nottingham City Hospital. Dr Lim is also chair of the Pandemic Influenza Clinical Management Guidelines Committee

Competing interests: None declared

Pneumonia X-ray

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