In 2019, lower respiratory tract infections affected 489 million people worldwide, and were the cause for approximately 2.5 million deaths. Children <5 years old and adults >70 years old were the populations most affected by pneumonia. Mortality was highest in patients aged >70 years old. Lower respiratory tract infections were the leading cause of infectious disease mortality worldwide in 2019.[4][5]

A literature review found that the overall annual incidence of CAP in Europe is between 1.07 and 1.2 per 1000 person-years and 1.54 and 1.7 per 1000 people.[6] The incidence of CAP increases with age to 14 per 1000 person-years in adults aged ≥65 years, and the incidence of CAP appears to be significantly higher in men than in women.[6] It is the fifth leading cause of mortality in Europe.[7] Estimates of mortality among patients range from 1% to 5% in outpatients, from 5.7% to 14% in general wards, and from 34% to 50% in the intensive care unit (especially in ventilated patients).[8][9] Another study reported that mortality rates of CAP in Europe vary widely from country to country, ranging between <1% and 48%.[10] The mortality rate for pneumococcal pneumonia is about 5%, rising to between 6% and 30% in adults with associated bacteraemia.[11][12]

Risk factors

Incidence increases significantly with age. Very advanced age has been associated with higher mortality from CAP.[34]

Approximately 10% to 18% of all patients hospitalised for pneumonia are nursing home residents. Mortality in these patients may reach 55%.[35][36] Patients in residential homes who develop pneumonia have traditionally been considered to have healthcare-associated pneumonia (HCAP) and not CAP. However, this definition has been criticised because it is not able to distinguish patients at risk for resistant pathogens, and each patient ought to be evaluated individually.

Associated with a 2- to 4-fold increased risk of CAP.[6] Data from one study conducted in patients with CAP compared the outcome of patients with and without COPD and found that the presence of COPD was an independent risk factor for mortality.[37]

Colonisation with pathogenic bacteria is frequent in smokers and presents an increased risk of lung infections, especially pneumococcal pneumonia.[38] One study of bacterial pneumonia found that HIV-infected smokers had >80% higher risk of developing pneumonia than those who had never smoked.[12][39] Another study showed that current smokers with pneumococcal CAP often develop sepsis and require hospitalisation at a younger age despite having fewer comorbid conditions than older patients.[40] Current and former smokers are more likely to develop CAP than never-smokers.[41] Passive smoking at home is a risk factor for CAP in people aged 65 years or older.[41][42]

There is clear evidence that alcohol consumption increases the risk for CAP. A meta-analysis of 14 studies found that people who consumed alcohol at all or in higher amounts had an 83% higher risk of CAP compared to people who consumed no alcohol or lower amounts (relative risk of 1.83).[43] Consumption of 24 g, 60 g, and 120 g of pure alcohol daily has been shown to result in a relative risk for incident CAP of 1.12 (95% CI, 1.02-1.23), 1.33 (95% CI, 1.06-1.67), and 1.76 (95% CI, 1.13-2.77), respectively, relative to non-drinkers.[44]

Oral and respiratory bacteria in dental plaques are shed into the saliva and can then be aspirated into the lower respiratory tract to cause infection. Aspiration pneumonia is one of the most serious problems in older patients. Low-quality evidence suggests that professional oral health care measures (e.g., brushing, swabbing, denture cleaning, mouth rinses) may reduce mortality due to pneumonia in nursing home residents compared to usual care.[45]

CAP is one of the most common adverse effects associated with use of proton-pump inhibitors.[46] This is thought to be due to a decrease in gastric acid secretion, which allows pathogens to colonise the upper respiratory tract more easily. Outpatient use of these drugs is associated with a 1.5-fold increased risk of CAP.[47] H2 antagonists may also be associated with an increased risk of CAP.[48]

Regular contact with children is associated with an increased risk of CAP.[49] Two studies have reported that having children in the household increases the adjusted odds ratio from 1.00 for households with no children to 3.2, or 3.41 for households with 3 or more children.[50][51]

Associated with a moderate increase in the risk of CAP. The main reasons are the increased risk of aspiration, hyperglycaemia, decreased immunity and impaired lung function, and coexisting morbidity.

One study found that diabetes (type 1 and type 2) was a risk factor for pneumonia-linked hospitalisation. Another study[52] reported that pre-existing diabetes was associated with a higher risk of death after hospitalisation for CAP compared with patients hospitalised for non-infectious illnesses.[53] The risk of severe pneumococcal bacteraemia is also higher in diabetic patients.[54]

A significant risk factor for mortality in patients with CAP.[55][56]

It is known that bacterial infections occur in 32% to 34% of hospitalised patients with cirrhosis, and approximately 15% of these infections are pneumonia (the third most common cause of infection in these patients).[57] One study reported that chronic liver disease is a risk factor for pulmonary complications in patients hospitalised with pneumococcal pneumonia.[58]

A case-control study found that prescribed opioids, especially those with immunosuppressive properties or higher doses, are associated with an increased risk of CAP in people with and without HIV infection.[59]

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