(1) University of Arizona, Tucson, United States
(2) Zuckerman College of Public Health, Division of Epidemiology and Biostatistics
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Studies of foodborne diseases, both to identify the causes of sporadic illnesses and investigation of outbreaks, typically utilize case-control study designs. However, this methodology requires intensive time and resources and is prone to selection and recall biases. Case-case studies have recently been utilized as alternatives. These study designs can be conducted in less time, with far fewer resources and, given the highly selective nature of foodborne case reporting, both selection and recall bias are reduced. Considerable variation remains, however, on how these studies are implemented and how effect measures are interpreted. The aim of this paper is to provide a set of criteria to systematically and consistently choose comparison cases for use in these case-case studies.
Materials and methods
Recent case-case and case-control study designs for foodborne diseases were systematically identified and reviewed on criteria for selection of cases and comparison groups, interpretation of effect measures, source of bias, and resource utilization. Use of this study design for different study goals, outbreak investigation or sporadic disease transmission, were evaluated.
Standardized procedures for selection of comparison cases, common terminology, and effect measures are proposed for case-case study designs, based on whether the study aim is to investigate a foodborne disease outbreak or to study trends in routine transmission. Examples of valid interpretations of resulting odds ratios from the different designs are provided.
Standardization of study design terminology and interpretation, based on the case type, will assist public health agencies and researchers in the effective and appropriate use of this design. The recommendations will allow more comparable results and, potentially, more efficient and timely identification of the cause of a foodborne outbreak.