Definitions of coverage
As the use of a new, sterile needle and syringe for injecting is the surest method of avoiding blood borne virus infection in injectors, and because lack of immediate availability of sterile injecting equipment is the main driver of sharing, this calculator has been developed to enable local estimation and modelling of coverage. The tool estimates 'coverage' defined as 'the percentage of injections of illicit drugs for which a new needle and syringe has been provided'.

'Coverage' is a term that has been used in the description of the provision or reach of health care services for many years¹, and which has been adapted for use to describe the provision of injecting equipment to injecting drug users in an imprecise way². There is no one agreed definition of coverage for all purposes and so the important issue is to understand the definition used and any assumptions underlying its use.

References
1. Hogarth, J. Glossary of Health Care Terminology. Copenhagen: WHO/EURO; 1975.
2. Sharma, M. Burrows, D. Bluthenthal, R. Coverage of HIV prevention programmes for injection drug users: confusions, aspirations, definitions and ways forward. Int J Drug Policy. 2007 March; 18(2): 92–98.