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. 2018 Oct 10;17:36. doi: 10.1186/s12941-018-0289-2

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© The Author(s) 2018

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 1 — Search strategy and study selection flow chart. This is a flow chart illustrating which databases were searched and the number of articles found from each database. This flow chart also documents the screening process and reasons for the exclusion of articles from the review, as well as the number of articles removed at each screening step