Case series

Abstract: Case series are a commonly reported study design, but the label "case series" is used inconsistently and sometimes incorrectly. Mislabeling impairs the appropriate indexing and sorting of evidence. This article tries to clarify the concept of case series and proposes a way to distinguish them from cohort studies. In a cohort study, patients are sampled on the basis of exposure and are followed over time, and the occurrence of outcomes is assessed. A cohort study may include a comparison group, although this is not a necessary feature. A case series may be a study that samples patients with both a specific outcome and a specific exposure, or one that samples patients with a specific outcome and includes patients regardless of whether they have specific exposures. Whereas a cohort study, in principle, enables the calculation of an absolute risk or a rate for the outcome, such a calculation is not possible in a case series.

Abstract: Objectives: Tuberculosis (TB) disease adversely affects mother and child, and strategies to control TB in this group are important. The aim of this study was to analyze the epidemiology of TB in pregnancy, and to establish whether pregnancy is an independent risk factor for TB.Methods: The United Kingdom–wide cohort study was based on the General Practitioner Research Database (GPRD), enrolling all women with pregnancies between 1996 and 2008. Incidence rates and incidence rate ratios (IRRs) of TB events during pregnancy, 6 months postpartum, and outside pregnancy were calculated and compared by Poisson regression. A nested self-controlled case series compared the risk of TB in these periods, adjusting for individual and time-bound confounders.Measurements and Main Results: The crude TB rate for the combined pregnancy and postpartum period was 15.4 per 100,000 person-years, significantly higher than outside of pregnancy (9.1 per 100,000 person-years; P = 0.02). Adjusting for age, region, and socioeconomic...