Name	Info	Provider	Link
	subscription/membership/fee required	Ovid Technologies, Inc.	http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=linkout&SEARCH=21881120.ui
	free resource	PubMed Central	https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/21881120/
	free resource	Europe PubMed Central	https://europepmc.org/abstract/MED/21881120
	subscription/membership/fee required	Silverchair Information Systems	https://academic.oup.com/jid/article-lookup/doi/10.1093/infdis/jir466
	free resource	Spiral, Imperial College Digital Repository	http://hdl.handle.net/10044/1/19646