Background: The early detection of infectious disease outbreaks can reduce the ultimate size of the outbreak, with lower overall morbidity and mortality due to the disease. Numerous approaches to the earlier detection of outbreaks exist, and methods have been developed to measure progress on timeliness. Understanding why these surveillance approaches work and do not work will elucidate key drivers of early detection, and could guide interventions to achieve earlier detection. Without clarity about the conditions necessary for earlier detection and the factors influencing these, attempts to improve surveillance will be ad hoc and unsystematic. Methods: A systematic review was conducted using the PRISMA framework (Preferred Reporting Items for Systematic Reviews and Meta-analyses) to identify research published between January 1, 1990 and December 31, 2015 in the English language. The MEDLINE (PubMed) database was searched. Influencing factors were organized according to a generic five-step infectious disease detection model. Results: Five studies were identified and included in the review. These studies evaluated the effect of electronic-based reporting on detection timeliness, impact of laboratory agreements on timeliness, and barriers to notification by general practitioners. Findings were categorized as conditions necessary for earlier detection and factors that influence whether or not these conditions can be in place, and were organized according to the detection model. There is some evidence on reporting, no evidence on assessment, and speculation about local level recognition. Conclusion: Despite significant investment in early outbreak detection, there is very little evidence with respect to factors that influence earlier detection. More research is needed to guide intervention planning.
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