Epidemiology
Community-acquired pneumonia (CAP) is estimated to result in approximately 1.2 million emergency department visits, 740,000 hospitalizations, and 41,000 deaths annually in the United States.[3][4] One 2015 population-based surveillance study estimated an annual incidence of CAP as 24.8 cases per 10,000 adults (95% confidence interval, 23.5 to 26.1) with the highest rates among adults ages 65-79 years (63.0 cases per 10,000 adults) and those age 80 years or older (164.3 cases per 10,000 adults).[5]
In 2019, lower respiratory tract infections affected 489 million people worldwide, and were the cause for approximately 2.5 million deaths. Adults >70 years old were the populations most affected by pneumonia and mortality was highest in these patients. Lower respiratory tract infections were the leading cause of infectious disease mortality worldwide in 2019.[6][7]
Risk factors
Incidence increases significantly with age. Very advanced age has been associated with higher mortality from community-acquired pneumonia.[42]
Approximately 10% to 18% of all patients hospitalized for pneumonia are nursing home residents. Mortality in these patients may reach 55%.[43][44] Patients in residential homes who develop pneumonia have traditionally been considered to have healthcare-associated pneumonia (HCAP) and not community-acquired pneumonia. However, this definition has been criticized because it is not able to distinguish patients at risk for resistant pathogens, and each patient ought to be evaluated individually.
Colonization with pathogenic bacteria is frequent in smokers and presents an increased risk of lung infections, especially pneumococcal pneumonia.[46] One study of bacterial pneumonia found that HIV-infected smokers had >80% higher risk of developing pneumonia than those who had never smoked.[47][48] Another study showed that current smokers with pneumococcal community-acquired pneumonia (CAP) often develop sepsis and require hospitalization at a younger age despite having fewer comorbid conditions than older patients.[49] Current and former smokers are more likely to develop CAP than never-smokers.[50] Passive smoking at home is a risk factor for CAP in people aged 65 years or older.[50][51]
There is clear evidence that alcohol consumption increases the risk for community-acquired pneumonia (CAP). One 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).[52] 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 to 1.23), 1.33 (95% CI 1.06 to 1.67), and 1.76 (95% CI 1.13 to 2.77), respectively, relative to nondrinkers.[53]
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. However, the effect of these measures on preventing pneumonia remains unclear.[54]
Community-acquired pneumonia (CAP) is one of the most common adverse effects associated with use of proton-pump inhibitors.[55] This is thought to be due to a decrease in gastric acid secretion, which allows pathogens to colonize the upper respiratory tract more easily. Outpatient use of these drugs is associated with a 1.5-fold increased risk of CAP.[56] H2 antagonists may also be associated with an increased risk of CAP.[57]
Other drugs that have been independently associated with an increased risk for CAP include inhaled corticosteroids (especially at higher doses), antipsychotics (especially atypical antipsychotics and in older people), and antidiabetic drugs.[58]
Regular contact with children is associated with an increased risk of community-acquired pneumonia.[59] 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.[60][61]
Patients with HIV infection are more susceptible to bacterial community-acquired pneumonia (CAP). Although antiretroviral therapy has improved the immune response and reduced the incidence of CAP, it remains a major cause of morbidity and mortality in these patients, in part because they show altered immunity and because immune activation persists. Mortality in HIV-infected patients with CAP ranges from 6% to 15%.[62]
Associated with a moderate increase in the risk of community-acquired pneumonia (CAP). The main reasons are the increased risk of aspiration, hyperglycemia, 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 hospitalization. Another study reported that pre-existing diabetes was associated with a higher risk of death after hospitalization for CAP compared with patients hospitalized for noninfectious illnesses.[63][64] The risk of severe pneumococcal bacteremia is also higher in diabetic patients.[65]
It is known that bacterial infections occur in 32% to 34% of hospitalized patients with cirrhosis, and approximately 15% of these infections are pneumonia (the third most common cause of infection in these patients).[68] One study reported that chronic liver disease is a risk factor for pulmonary complications in patients hospitalized with pneumococcal pneumonia.[69]
One case-control study found that prescribed opioids, especially those with immunosuppressive properties or higher doses, are associated with an increased risk of community-acquired pneumonia in people with and without HIV infection.[70]
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