A rise in people injecting cocaine and homelessness are the key factors behind a "perfect storm" that has resulted in a tenfold increase in HIV infection among drug users in Glasgow city centre, research has found.

In a seven-year study, experts from Glasgow Caledonian University (GCU) and Health Protection Scotland examined the drivers behind the UK's largest HIV outbreak in more than 30 years in Glasgow.

More than 100 new cases of the infection were identified among drug users in the city between 2015 and 2017.

Before that the number of new cases had "remained stable" at about 15 a year among drug users across all of Scotland.

Dr Andrew McAuley, a senior research fellow in blood borne viruses at GCU, and the lead author of the paper, said there had been "a hugely significant increase in the prevalence of HIV infection in the population of people who inject drugs in Glasgow, largely driven by an outbreak of HIV first detected in 2015".

He also claimed the study, published in the Lancet HIV medical journal, "provides further justification" for those arguing for a safe drugs consumption room to be set up in Glasgow city centre - with more than nine out of ten of those diagnosed with HIV now successfully engaged in treatment.

Speaking about the number of drug users with the virus, Dr McAuley said: "The prevalence of HIV has been low and stable in this population since major outbreaks of HIV in the 1980s in Edinburgh and Dundee.

"However, the prevalence of HIV in Glasgow has increased tenfold among people who inject drugs in the past seven years, from just 1% to over 10% in the city centre.

"The key drivers of infection are an increase in cocaine injecting, and homelessness.

"We also have a large population of people who inject in public places in Glasgow at a time when HIV has re-emerged.

"A combination of these factors has created a perfect storm for rapid transmission of HIV among people who inject drugs in Glasgow."

The research, carried out together with NHS Greater Glasgow and Clyde and the University of the West of Scotland, found the number of drug users with HIV went from one in 87 in 2011-12 to 25 out of 231 in 2017-18 - with the proportion of users who were infected going from 1.1% to 10.8%.

The study used information from four in-depth surveys - collectively called the Needle Exchange Surveillance Initiative (NESI) - conducted between 2011 and 2018 and involving almost 4000 people who inject drugs in Greater Glasgow and Clyde.

Dr Norah Palmateer, a GCU senior research fellow, who co-authored both the reports,said: "We found that the sharp rise in cocaine injecting identified in NESI is the single largest risk factor for acquiring HIV in Glasgow, possibly because it is likely to cause individuals to inject more often which, in turn, makes them more vulnerable to infection."

Scottish Public Health Minister Joe FitzPatrick said: "Prevention of HIV infection remains a priority for the Scottish Government. There is absolutely no room for complacency.

"I have visited the team in Glasgow who are working to tackle the HIV outbreak amongst people who inject drugs and was impressed by their commitment to collaborative working to make sure the most vulnerable people get the support they need to access testing and treatment."

He added: "These issues underline why we support Glasgow Health and Social Care Partnership's proposals to introduce a secure, medically supervised consumption facility.

"We must be willing to back innovative, evidence-based approaches that can make a real difference to people's lives."