The role of biomarkers in community-acquired pneumonia: predicting mortality and response to adjunctive therapy

Community-acquired pneumonia (CAP) accounts for 1.3 million hospitalizations each year in the USA, at an annual cost of $8.4 billion [1]. The average duration of hospitalization for CAP managed on the ward is 6 days, at a cost of $7,500. If intensive care unit (ICU) admission (for severe CAP) is required, then the stay increases to 23 days, at a cost of $21,144. The average cost for managing pneumonia in the UK was estimated at ￡100 per episode, as compared with ￡1,700 to ￡5,100 for hospitalized (severe CAP) patients. Hospitalization accounted for 87% of the total annual cost [2,3].Although CAP is very common, it remains a common cause of death. Hence, severe CAP has been reported to be the largest single cause of mortality from infectious diseases in industrialized countries [4]. For example, a study conducted in the USA compared outcomes in more than 150,000 patients aged over 65 years who were hospitalized for CAP with those in 800,000 control individuals matched for age, sex and race who were admitted to hospital for conditions other than pneumonia [4]. The in-hospital mortality rate among CAP patients was significantly higher, at 11%, than that in non-CAP patients (5.5%; P < 0.001). Surprisingly, the 1-year mortality rate among CAP patients remained significantly higher than that in control individuals (41% versus 29%; P < 0.001). Thus, mortality rates in patients with severe CAP remain high and are discussed in detail elsewhere in this supplement [5]. The factors that underlie the poor short-term and long-term survival rates in patients with CAP and severe CAP are not yet completely understood. However, aspects of the pathophysiology of the disease, reflected in some of the recently described biomarkers and genomic markers, may contribute to increased understanding.Hence, in addition to being an infectious disease, severe CAP elicits major systemic responses that could also allow this pathology to be classified as inflammatory (indicated by systemic release of