As reported in the Evening Times, seven cases of E.coli 0157 were initially reported, with NHS Greater Glasgow and Clyde (NHSGCC) which could be linked to burgers sold inside the £125million venue.
The period of time under investigation was January 17 to 25, which included Top Gear live shows, a Del Amitri gig and a Celtic Connections event.
The Hydro holds up to 12,000 people, meaning that over the course of five Top Gear shows and the other two events, up to 84,000 were potentially exposed to the bug.
It has since been confirmed that all those affected, including the four latest cases, attended the Hydro over the weekend when the Top Gear shows were being held.
All 15 cases are recovering at home.
Two cases are from the NHSGGC area, three are from the NHS Lanarkshire area, five cases are from NHS Lothian, two are from NHS Highland, two cases from NHS Forth Valley and one is from Cumbria.
They range in age from nine-years-old to 61.
Dr Eleanor Anderson, consultant in Public Health Medicine, NHSGGC said: "Investigations are ongoing and while there is no conclusive evidence our investigations have indicated that there may be a link to the consumption of burgers at the SSE Hydro.
"Glasgow City Council Environmental Health Officers are working closely with the vendors to ensure all appropriate food hygiene standards are being met.
"I would ask anyone who has attended the Hydro, particularly between 17 and 19 January and who has experienced or is continuing to experience symptoms including stomach cramps, diarrhoea, nausea and fever to contact their GP."