To improve the understanding of the determinants of prognosis and accurate risk stratification in community-acquired pneumonia (CAP).
Multicentre collaboration of prospective cohorts.
6 cohorts from the USA, Canada, Hong Kong and Spain.
From a published meta-analysis of risk stratification studies in CAP, the authors identified and pooled individual patient-level data from six prospective cohort studies of CAP (three from the USA, one each from Canada, Hong Kong and Spain) to create the International CAP Collaboration Cohort. Initial essential inclusion criteria of meta-analysis were (1) prospective design, (2) in English language, (3) reported 30-day mortality and transfer to an intensive or high dependency care and (4) minimum 1000 participants. Common baseline patient characteristics included demographics, history and physical examination findings, comorbidities and laboratory and radiographic findings.
Primary and secondary outcome measures
This paper reports the rationale, hypotheses and analytical framework and also describes study cohorts and patients. The authors aim to (1) compare the prognostic accuracy of existing CAP risk stratification tools, (2) assess patient-level determinants of prognosis, (3) improve risk stratification by combined use of scoring systems and (4) understand prognostic factors for specific patient groups.
The six cohorts assembled from 1991 to 2007 included 13 784 patients (median age 71 years, 54% men). Aside from one randomised controlled study, the remaining five were cohort studies, but all had similar inclusion criteria. Overall, there was 0%–6% missing data. A total of 6159 (44%) had severe pneumonia by Pneumonia Severity Index class IV/V. Mortality at 30 days was 8% (1036). Admission to intensive care or high dependency unit was also 8% (1059).
International CAP Collaboration Cohort provides a pooled multicentre data set of patients with CAP, which will help us to better understand the prognosis of CAP.
This paper reports the rationale, hypotheses and analytical framework and also describes study cohorts and patients. We aim to
compare the prognostic accuracy of existing CAP risk stratification tools;
assess patient-level determinants of prognosis;
improve risk stratification by combined use of scoring systems;
understand prognostic factors for specific patient groups.
The International CAP Collaboration Cohort (ICCC) as described in this report will be able to provide better understanding of determinants of outcomes in CAP. Examples of such development include comparison of commonly and less commonly known CAP severity scoring systems and identification of characteristics of CAP patients with poor outcome (30-day mortality) despite non-severe status of severity score.
In view of the large sample size, the ICCC cohort will be able to provide the determinants of outcomes in patient groups with specific conditions such as cardiovascular and respiratory diseases taking into account case mix and individual prognostic indicators.
The ICCC cohort will be of benefit to the CAP research community and help define a future agenda for research, as well as helping clinicians make better clinical decisions for patients with CAP.
Strengths and limitations of this study
The ICCC is a multicentre/multiethnic cohort where all collaborating groups defined pneumonia based on clinical features and the presence of CXR evidence of pneumonia. The major strengths of ICCC are prospective study design, inclusion of CAP patients spanning across wide age range, ethnicity, different healthcare settings and large sample size. Potential areas of improvement in assessment of CAP might be identification of at-risk patients with pneumonia who have been initially assessed as non-severe CAP. With large sample size, ICCC may provide an opportunity to identify characteristics of such individuals. Based on this work, risk assessment may be applied at more than one point in time in order to observe temporal trends in recovery or deterioration in future CAP research and clinical practice.
There were multiple observers and data collections across several centres. However, all cohorts followed the strict criteria in data collection as described in table 1. Furthermore, the data collected were objective measures such as age and urea level, thereby ruling out potential observer bias. The process of care between hospitals may be variable. There may be a variation in clinical management between different hospitals and in different healthcare setting between the various countries such as there may be important variations in antibiotic use, patterns of infective micro-organisms, care protocols and treatment guidelines. Other limitations to consider are biomarkers, healthcare provider and site characteristics. The patients were enrolled into the study at different time periods. However, this presents an opportunity to compare and contrast different healthcare systems to better understand the variation in healthcare setting and outcomes. Since all six studies used the Pneumonia Severity Index (PSI) for risk stratification, this can have implications, for example, patients who scored non-severe at initial assessment (low PSI) but might have had worse outcome are under-represented if such patients were sent home. This could contribute to attenuation of estimates in low PSI group. Nevertheless, it is possible that these patients would have presented again to the medical centre if/when deterioration occurred. Cohorts that only had data on CURB-related variables and cohorts with smaller sample sizes were not included in the ICCC, and this may introduce some degree of selection bias. Nevertheless, this should not have any effect on the internal relationship between the predictors and outcomes of interest.