Influenza

What it is

Influenza is a viral illness. Influenza viruses sit among the viral causes of infective rhinitis, with rhinoviruses, RSV, parainfluenza and adenoviruses, and among the viral causes of acute otitis media, with RSV, parainfluenza and adenovirus. There are three types of influenza virus, A, B and C, and types A and B account for the majority of clinical disease. Seasonal influenza still accounts for significant morbidity and mortality in the UK each winter, with the influenza season typically starting in the middle of November.

Causes and risk

High-risk individuals, those at a high risk of influenza-related complications, include those with chronic lung disease; cardiovascular (excluding hypertension), renal, hepatic, hematologic, or neurologic disease; or age >65. Children on long-term aspirin therapy, and pregnant and postpartum women are also considered high risk. Pregnant women in particular are at increased risk of complications of influenza, including hospitalization and mortality.

How it presents

Influenza gives a rapid onset of fever, nausea, and sore throat, with negative pulmonary findings.

Where influenza viruses cause infective rhinitis, the features are mucoid rhinorrhea, malaise, nasal obstruction and sneezing. Secondary bacterial infection gives nasal congestion, purulent rhinorrhea and facial dental pain, and it is suspected in patients with persistent symptoms of URTI beyond 10-14 days.