Pneumonia is an infection of the lung tissue, as opposed to an infection mainly affecting the bronchi such as bronchitis. Microorganisms, fluid and inflammatory cells in pneumonia block the alveoli, replacing the air.6,8

Bacteria or viruses are usually implicated, but fungi cause some cases. Pneumococcal pneumonia accounts for up to 60% of cases CAP cases. The most common pathogen is Streptococcus pneumoniae, but other frequently detected bacteria include Haemophilus influenzae and Staphylococcus aureus.6,7,9

Among the viruses – a common cause of pneumonia in young children – are respiratory syncytial virus (RSV) and sometimes influenza type A or B.9

Aspiration pneumonia can arise from vomit or a foreign object entering the lungs, such as by breathing in a peanut, smoke or chemicals.9

Groups at higher risk of developing pneumonia include: 9

·       babies and young children

·       the elderly

·       smokers

·       excessive alcohol drinkers

·       people with comorbidities including heart, kidney or liver conditions, asthma, cystic fibrosis, or diabetes

·       immunocompromised people.

There is also a risk of hospital-acquired pneumonia, for example in people intubated with a mechanical respirator, or because of recent antibiotic use, or simply due to their resistance to infection being reduced because of the illness that brought them to hospital in the first place.10

The increase in diseases such as flu over the winter months adds to the risk of contracting pneumonia.