Epidemiology
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.[3][4]
In the US, the annual incidence of CAP has been estimated at 24.8 cases in 10,000 adults.[5] Pneumonia and influenza, when considered together, were the eighth leading cause of death (13.5 deaths in 100,000 population) and the leading infectious cause in the US in 2016.[6] In the US, the annual rate of hospitalization for adults ≥65 years old ranges from 847 to 3500 per 100,000 persons; the rate is lower for adults <65 years old (89 to 1138 per 100,000 persons).[7]
Risk factors
Incidence increases significantly with age. Very advanced age has been associated with higher mortality from CAP.[37]
Approximately 10% to 18% of all patients hospitalized for pneumonia are nursing home residents. Mortality in these patients may reach 55%.[38][39] 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 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.[41] One study of bacterial pneumonia found that HIV-infected smokers had >80% higher risk of developing pneumonia than those who had never smoked.[42][43] Another study showed that current smokers with pneumococcal CAP often develop sepsis and require hospitalization at a younger age despite having fewer comorbid conditions than older patients.[44] Current and former smokers are more likely to develop CAP than never-smokers.[45] Passive smoking at home is a risk factor for CAP in people aged 65 years or older.[45][46]
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).[47] 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.[48]
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.[49]
CAP is one of the most common adverse effects associated with use of proton-pump inhibitors.[50] 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.[51] H2 receptor antagonists may also be associated with an increased risk of CAP.[52]
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 medications.[53]
Patients with HIV infection are more susceptible to bacterial 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%.[57]
Associated with a moderate increase in the risk of 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.[58][59] The risk of severe pneumococcal bacteremia is also higher in diabetic patients.[60]
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).[63] One study reported that chronic liver disease is a risk factor for pulmonary complications in patients hospitalized with pneumococcal pneumonia.[64]
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.[65]
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