The mortality rate associated with community-acquired pneumonia (CAP) is very low in most ambulatory patients and higher in patients requiring hospitalization, being as high as 37 percent in patients admitted to the intensive care unit (ICU).
Adherence to guideline recommendations has been associated with reductions in the proportion of low-risk patients admitted to the hospital and, for those admitted, the duration of hospitalization. Some observational studies have also noted substantial reductions in mortality, but guideline adherence could represent a surrogate marker for other aspects of clinical care.
A number of risk factors for mortality have been identified. Having two or three of the following variables have been associated with high risk in several studies: blood urea nitrogen greater than 20 mg/dL (7 mmol/L), diastolic blood pressure less than 60 mmHg, and/or respiratory rate above 30 per minute. These three variables plus confusion and age greater than 65 years constitute the CURB-65 score; patients with 0 or 1 of these factors are at low risk and can usually be treated as outpatients. Underlying comorbidity and the cause of pneumonia also affect the mortality risk.
It has been estimated that 6 to 15 percent of hospitalized patients with CAP do not respond to initial antibiotic therapy within 72 hours. These patients have a much higher mortality rate than those who respond.
Among patients with CAP who require hospitalization, prior pneumococcal and influenza vaccination have been associated with better outcomes.
CAP has been associated with both short- and long-term risk of cardiovascular events.
The British Thoracic Society found a 21-fold increase in mortality in patients who had two or more of the following findings
●Blood urea nitrogen greater than 20 mg/dL (7 mmol/L)
●Diastolic blood pressure less than 60 mmHg
●Respiratory rate above 30 per minute
The predictive value of these findings was validated in 245 patients hospitalized for CAP in the United States, 20 of whom (8.2 percent) died． The presence of all three variables predicted a ninefold greater risk for death with 70 percent sensitivity and 84 percent specificity.
These three findings plus confusion (based upon a specific mental test or new disorientation to person, place, or time) and age greater than 65 years constitute the five factors at presentation that make up the CURB-65 score, which is a prediction rule for prognosis used to determine whether a patient should be admitted to the hospital.
Among the 718 patients (mean age 64) in the derivation cohort of CURB-65, 30-day mortality was 0.7, 2.1, 9.2, 14.5, and 40 percent for 0, 1, 2, 3, or 4 factors, respectively; only a small number of patients had five factors．These findings were validated in a subsequent cohort of 3181 patients: 30-day mortality was 0.6, 3.0, 6.1, and 14.3 percent for 0, 1, 2, or 3 or more factors, respectively．
The authors of the original CURB-65 report suggested that patients with a CURB-65 score of 0 to 1, who comprised 45 percent of the original cohort and 61 percent of the later cohort, were at low risk and could probably be treated as outpatients, those with a score of 2 should be admitted to the hospital, and those with a score of 3 or more should be assessed for care in the intensive care unit (ICU), particularly if the score was 4 or 5.
Pneumonia severity index
The Pneumonia Severity Index was derived and validated as part of the Pneumonia Patient Outcomes Research Team (PORT) prospective cohort study for the purpose of identifying patients with CAP at low risk for mortality in order to aid with the decision of which patients require hospital admission. Points are assigned based upon gender, age, nursing home residence, comorbidities, physical examination findings, and laboratory and radiographic findings. It is widely used for predicting 30-day mortality．The PSI is described in detail separately.
Although the PSI was designed to predict 30-day mortality, in a population-based cohort study in which patients were followed for a median of 3.8 years, it also predicted long-term mortality．
Prior pneumococcal and influenza vaccination appear to improve outcomes in patients with CAP.
Pneumococcus — The potential efficacy of pneumococcal vaccination was illustrated in a prospective, multicenter, population-based cohort study of 3415 adults hospitalized with CAP in which the primary outcome was the composite of in-hospital mortality or ICU admission． Among these patients, 22 percent had previously been vaccinated with the 23-valent pneumococcal polysaccharide vaccine (PPSV23). PPSV23 was associated with a significant reduction in the primary outcome (10 versus 21 percent, propensity-adjusted odds of death or ICU admission 0.62, 95% CI 0.42-0.92). Virtually all of the benefit was due to a lower rate of ICU admission. Among over 2400 patients eligible for PPSV23 at hospital discharge, only 9 percent were vaccinated.
Benefit was also noted in a retrospective analysis of 63,000 adults hospitalized with CAP, 12 percent of whom had a record of prior pneumococcal vaccination. The following significant benefits were noted in the vaccination group compared with those who had not received the pneumococcal vaccine:
●A lower rate of all- cause mortality during hospitalization (adjusted odds ratio [OR] 0.50; 95% CI 0.43-0.59)
●A lower rate of respiratory failure (adjusted OR 0.67; CI 0.59-0.76)
●A shorter median length of stay (4.5 versus 6.5 days)
Two additional studies demonstrated the efficacy of PPSV23 in older patients．The benefit of PPSV23 was demonstrated in a population-based case-control study of persons 60 years and older (mean age 73) from Spain．The study assessed 88 case patients with invasive pneumococcal disease and 176 matched controls. A lower rate of prior PPSV23 was found in the case patients than the controls (39 versus 59 percent)．
In a double-blind randomized controlled trial of 1006 nursing home patients (mean age 85 years) in Japan, all-cause pneumonia and pneumococcal pneumonia were significantly more frequent in the placebo group than in the PPSV23 group (91 versus 55 cases per 1000 person-years and 32 versus 12 cases per 1000 person-years, respectively)．Death from pneumococcal pneumonia was significantly higher in the placebo group than in the PPSV23 group (35 versus 0 percent).
Prognosis and outcomes of patients with community-acquired pneumonia. A meta-analysis. - PubMed - NCBI
Processes and outcomes of care for patients with community-acquired pneumonia: results from the Pneumonia Patient Outcomes Research Team (PORT) cohor... - PubMed - NCBI
Association of diagnostic coding with trends in hospitalizations and mortality of patients with pneumonia, 2003-2009. - PubMed - NCBI
Efficacy of 23-valent pneumococcal vaccine in preventing pneumonia and improving survival in nursing home residents: double blind, randomised and pla... - PubMed - NCBI