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Reducing contamination risk in cluster-randomised infectious disease intervention trials


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McCann, Robert S, van den Berg, Henk, Takken, Willem, Chetwynd, Amanda G, Giorgi, Emanuele, Terlouw, Anja ORCID: and Diggle, Peter J (2018) 'Reducing contamination risk in cluster-randomised infectious disease intervention trials'. International Journal of Epidemiology.

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Background: Infectious disease interventions are increasingly tested using cluster-randomised trials (CRT). These trial settings tend to involve a set of sampling units, such as villages, whose geographic arrangement may present a contamination risk in treatment exposure. The most widely used approach for reducing contamination in these settings is the so-called fried-egg design, which excludes the outer portion of all available clusters from the primary trial analysis. However, the fried-egg design ignores potential intracluster spatial heterogeneity and makes the outcome measure inherently less precise. While the fried-egg design may be appropriate in specific settings, alternative methods to optimise the design of CRTs in other settings are lacking.

Methods: We present a novel approach for CRT design that either fully includes or fully excludes available clusters in a defined study region, recognising the potential for intracluster spatial heterogeneity. The approach includes an algorithm that allows investigators to identify the maximum number of clusters which could be included for a defined study region and maintain randomness in both the selection of included clusters and the allocation of clusters to either the treatment group or control group. The approach was applied to the design of a CRT testing the effectiveness of malaria vector control interventions in southern Malawi.

Conclusions: Those planning CRTs to evaluate interventions should consider the approach presented here during trial design. The approach provides a novel framework for reducing the risk of contamination among the CRT randomisation units in settings where investigators determine the reduction of contamination risk as a high priority and where intracluster spatial heterogeneity is likely. By maintaining randomness in the allocation of clusters to either the treatment group or control group, the approach also permits a randomisation-valid test of the primary trial hypothesis.

Item Type: Article
Subjects: WA Public Health > Health Problems of Special Population Groups > WA 395 Health in developing countries
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 750 Malaria
Faculty: Department: Clinical Sciences & International Health > Malawi-Liverpool-Wellcome Programme (MLW)
Digital Object Identifer (DOI):
Depositing User: Stacy Murtagh
Date Deposited: 31 Oct 2018 09:25
Last Modified: 29 Oct 2019 02:02


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