Influenza World Health Care Professionals

Young children experience high rates of influenza infection due to low levels of immunity from lack of prior exposure to the influenza virus. [1] They are also at risk of hospitalisation, with estimates suggesting that 1 in every 1,000 children aged 0–4 years with influenza will need to be admitted to hospital owing to complications of their illness. [2] Furthermore, death rates among children with influenza are estimated to be 0.8 per 1,000,000 child-cases each year, the majority because of secondary complications of the viral infection. [3]

Complications

Influenza is a major cause of respiratory illness in children [4] and can lead to serious secondary complications such as bronchitis and exacerbation of asthma. Certain complications of influenza, such as acute otitis media, laryngotracheobronchitis (croup) and febrile convulsions are more prominent in infants and young children than in adults. [5] Otitis media is the most common complication of influenza in children and can cause hearing problems leading to delayed speech development. [6]

The incidence rates for common influenza-related complications among children younger than 5 years are shown in the table below. [7]

Complication	Incidence of children aged <5 years with influenza who may develop common complications
Acute otitis media	28%
Acute pneumonia	6%
Seizures	1%

Reye’s syndrome is a rare and serious condition that is characterised clinically by profuse vomiting and lethargy that may lead to coma or death. It occurs most often in children aged 5–14 years who have an inborn mitochondrial enzyme abnormality which manifests upon exposure to certain viral disease (e.g. influenza) and the use of salicylates (e.g. aspirin) taken to relieve symptoms. [5, 8]
Early recognition and treatment are essential to minimise long-term neurological damage. Diagnostic criteria for Reye’s syndrome during an influenza epidemic are as follows: [9]

• recurrent nausea and vomiting
• acute onset of non-inflammatory encephalopathy with an altered level of consciousness
• normal results on lumbar puncture
• elevated serum transaminase levels (greater than 1.5-times normal)
• hypoprothrombinaemia
• elevated blood ammonia levels (greater than 1.5-times normal).

Although very few children develop Reye’s syndrome, the World Health Organization has advised that the use of aspirin should be avoided in children under the age of 18. [10]

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7. Poehling KA, Edwards KM, Weinberg GA, et al. The under-recognized burden of influenza in young children. N Engl J Med 2006; 355: 31-40.
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9. Corey L, Rubin RJ, Bregman D, Gregg MB. Diagnostic criteria for influenza B-associated Reye's syndrome: clinical vs. pathologic criteria. Pediatrics 1977; 60: 702–8.
10. World Health Organization: WHO interim guidelines on clinical management of humans infected by influenza A (H5N1). Available here.