Identification and selection of cases and controls in the Pneumonia Etiology Research for Child Health project

Abstract

Methods for the identification and selection of patients (cases) with severe or very severe pneumonia and controls for the Pneumonia Etiology Research for Child Health (PERCH) project were needed. Issues considered include eligibility criteria and sampling strategies, whether to enroll hospital or community controls, whether to exclude controls with upper respiratory tract infection (URTI) or nonsevere pneumonia, and matching criteria, among others. PERCH ultimately decided to enroll community controls and an additional human immunodeficiency virus (HIV)-infected control group at high HIV-prevalence sites matched on age and enrollment date of cases; controls with symptoms of URTI or nonsevere pneumonia will not be excluded. Systematic sampling of cases (when necessary) and random sampling of controls will be implemented. For each issue, we present the options that were considered, the advantages and disadvantages of each, the rationale for the methods selected for PERCH, and remaining implications and limitations.

Figure 1.

An illustration of case and control sampling proportional to the case detection rates. A small time lag is anticipated for controls frequency-matched to the month of enrollment of cases, due to the expected interval from observed cases to the communication of this target number to the field workers who recruit controls.

Figure 2.

An illustration of the patient flowchart. Abbreviations: OPD, outpatient department; ER, emergency room; ARI, acute respiratory infection; PERCH, Pneumonia Etiology Research for Child Health Study.