Epidemiology

More than 65,000 people develop pleural infections in the US and UK combined each year.[4] One study of working-age adults in the US found an overall incidence rate of community-acquired pneumonia of 10.6 in 1000 person-years.[5] Another study found that the incidence of non-ventilator hospital-acquired pneumonia in the US is 3.63 in 1000 patient-days.[6] Parapneumonic effusions may be caused by either community-acquired or hospital-acquired pneumonia. Between 20% and 57% of the 1 million patients hospitalised each year in the US with pneumonia develop a parapneumonic effusion.[7] Approximately 5% to 10% of parapneumonic effusions develop into empyemas.[8]​ There is some evidence that empyema is increasing in incidence in both adults and children, the reason for which is unknown.[9][10][11][12][13][14]

Empyema is more common in men, with a male to female ratio of approximately 2:1. It also has a bi-modal age distribution, occurring more in the sixth or seventh decade of life and in young children.[14]​ The incidence of parapneumonic effusion and empyema is approximately 3.3 in 100,000 children per year, and there is some evidence that this figure is increasing.[15][16]

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