Assessment of severity of community-acquired pneumonia

Community-acquired pneumonia (CAP) is the most common serious infection encountered in medical practice, with 1% to 10% of patients requiring admission to a hospital. The mortality rate of patients admitted is considerable, ranging from 5% to 25%. Motivated by the results of the British Thoracic Society (BTS) study, different investigators have identified several risk factors associated with a high mortality rate. The assessment of the severity of CAP can be determined at three stages: (1) At home or during the general practitioner's (GP) consultation; (2) In the hospital outpatient clinic or emergency room; and (3) In the medical ward and/or intensive care unit (ICU). At stage 1, medical history, symptoms, and signs (respiratory rate!) seem to be relevant. However, it is not easy for GPs to diagnose pneumonia with any degree of certainty because of the limited diagnostic tools available. Once a patient is referred to a hospital (stage 2), factors such as clinical presentation, comorbidities, and laboratory and radiographic factors must be determined to identify those patients who are at risk. BTS criteria (respiratory rate > or =30/min, diastolic blood pressure < or = 60 mm Hg, blood urea nitrogen >7 mmol/L), but also other combinations of criteria, are associated with a multiple-fold increased risk of death. However, most of these prognostic models have low positive predictive value, suggesting that the risk of death is overestimated when these models are implemented in daily practice. In general, younger patients without comorbidities can be treated in an outpatient setting; sometimes brief inpatient observation is necessary. Elderly patients, especially those with comorbidities and severe illness need inpatient care, sometimes resulting in treatment from an ICU. Severe CAP (stage 3) is defined as pneumonia associated with respiratory failure and/or hemodynamic instability requiring treatment in an ICU, and has a death rate varying from 21% to 54%. Pneumonia- and non-pneumonia-related complications are often observed. Adverse prognostic factors that have been reported in several studies are: advanced age, the presence of comorbidities, development of septic shock, need for mechanical ventilation (including use of positive end-expiratory pressure and FiO2 >60%), development of adult respiratory distress syndrome, progression of radiographic abnormalities, bacteremia (especially when due to P aeruginosa), non-pneumonia-related complications, and inadequate antibiotic treatment. To reduce mortality, prospective studies focusing on adverse prognostic factors at the start of and during antibiotic treatment are urgently needed at all three stages.