"Contaminated needles" refers to needles that have been infected with harmful substances, such as bacteria or viruses. These needles can spread diseases or infections to people if they are used for medical procedures or drug use. Full definition
(People infected with hepatitis C, often through contaminated needles from injection drug use, accounted for a large swath of paid donors.) (discovermagazine.com)
Unprotected sex between men remains the most common method of transmission, followed by sharing contaminated needles or having sex with people who fall into either of those categories. (scientificamerican.com)
These might, for example, include health workers injured accidentally by contaminated needles. (newscientist.com)