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Table 2 Methods and search strategy for review and transmission tree reconstruction

From: Role of healthcare workers in early epidemic spread of Ebola: policy implications of prophylactic compared to reactive vaccination policy in outbreak prevention and control

Methods  
Search strategy A compound search strategy was developed to identify all relevant open-source articles regardless of publication status. The initial search was undertaken via PubMed using the search terms outlined below. Further information was obtained by reviewing article bibliographies for relevant citations and a Google search to find open-source published articles, press articles, and other grey literature including outbreak updates, WHO roadmaps, WHO situation reports, and Morbidity and Mortality Weekly Reports from the Centres for Disease Control.
The purpose of the review is to outline potential policy implications for vaccine development, as opposed to defining detailed epidemic trees.
Search terms used Key words: Ebola, Ebola haemorrhagic fever, Ebolavirus, Ebola virus disease, transmission, transmission trees, epidemic, epidemic trees.
(("hemorrhagic fever, Ebola"[MeSH Terms] OR ("hemorrhagic"[All Fields] AND "fever"[All Fields] AND "Ebola"[All Fields]) OR "Ebola hemorrhagic fever"[All Fields] OR "Ebola"[All Fields] OR "Ebolavirus"[MeSH Terms] OR "Ebolavirus"[All Fields]) OR ("hemorrhagic fever, Ebola"[MeSH Terms] OR ("hemorrhagic"[All Fields] AND "fever"[All Fields] AND "Ebola"[All Fields]) OR "Ebola hemorrhagic fever"[All Fields] OR ("Ebola"[All Fields] AND "virus"[All Fields] AND "disease"[All Fields]) OR "Ebola virus disease"[All Fields])) AND ((("transmission"[Subheading] OR "transmission"[All Fields]) AND ("trees"[MeSH Terms] OR "trees"[All Fields] OR "tree"[All Fields])) OR (("epidemics"[MeSH Terms] OR "epidemics"[All Fields] OR "epidemic"[All Fields]) AND ("trees"[MeSH Terms] OR "trees"[All Fields] OR "tree"[All Fields])))
Inclusion criteria Studies and articles were eligible for inclusion if they reported human-to-human transmission chains and initial transmission chains from the primary or index case within each outbreak or country in multi-location epidemics. Details of occupational exposure of individuals in the transmission trees were also included where possible. There were no restrictions with regards to date of publication. The aim was to identify as many early epidemic trees as possible, and to include all which could be reliably identified as including HCW status to minimise bias.
Data extraction Data extraction was first undertaken using peer-reviewed literature. These data were supplemented by grey literature and press articles to add further information and fill in the gaps for the epidemic tree construction.
Approximate numbers have been used where precise numbers were not available, but in all cases conservative assumptions have been made to avoid overestimation of any effects identified.
Data analysis Initial analyses of the different vaccination strategies were undertaken in Microsoft Excel (2010). Using the initial transmission trees constructed, the number of cases that developed the disease and the number of cases averted were calculated for each vaccination strategy. All results are given as a percentage of averted cases by the total number of cases. The results are given per vaccination strategy and epidemic location.