STUDY DESIGN, TESTING, AND ANALYSIS
Although inferences regarding pneumonia etiology can be drawn from many different study designs, including cohort studies, case series, and treatment or intervention trials, the PERCH study has been designed as a case-control study that aims to enroll 6000 patients hospitalized for severe or very severe pneumonia and 6000 controls selected randomly from the community. The main reasons for this design are as follows: (1) the use of hospitalized patients, as opposed to those observed outside of facilities, is necessary to assure that we can safely collect a range of specimens from patients and that we gain the efficiency of testing only those with severe and very severe pneumonia; and (2) the inclusion of controls is important to guide the interpretation of results from the use of highly sensitive detection tests on upper respiratory tract specimens and to facilitate the identification of risk factors for pneumonia and/or specific etiologies. Although PERCH recognizes that pneumonia is an important illness in neonates and that important questions remain regarding the etiologies of serious pneumonia in this age group, it was considered sufficiently important and unique to require its own study, and thus PERCH focuses on children aged 1–59 months old.