More news from my uncle.
He was advised to report the incident to the police. The police have now treated the scene of the incident as a crime scene. The "junkie" was a known offender (who my uncle identified from a picture list) and is a know Hep B positive. Based on what was found at the crime scene, they are treating the placement of the syringe and associated damage as malicious intent.
No idea if the perpetrator has been arrested. No news back from the blood work. My uncle has been talking to police tirelessly for the last two days. He's quite stressed but apparently work is giving him their full support.