According to new research HIV infection rates amongst people who inject themselves with drugs appear to be on the rise and there are huge discrepancies worldwide.
A study using a range of data estimates there may be 3 million self-injecting drug users worldwide who are HIV positive.
Dr. Bradley Mathers and colleagues from the National Drug and Alcohol Research Center at the University of New South Wales, Sydney, Australia, used data gleaned from a number of peer-reviewed studies along with information from the United Nations agencies and international experts and have identified injected drug use in 148 countries.
The research revealed HIV infections among these kind of users was over 40% in nine countries - Estonia, Ukraine, Myanmar (Burma), Indonesia, Thailand, Nepal, Argentina, Brazil and Kenya.
Experts say the new data suggests there are increases in both the number of injecting drug users and the prevalence of HIV in users and it would be timely to educate people in countries where injecting drug use is common but the virus has not yet begun infecting users to a large degree.
The situation is a concern because used syringes can spread HIV and infected drug users are also more likely to engage in risky behaviour such as unprotected sex that can spread the virus that causes AIDS.
The researchers estimated that in 2007 nearly 16 million people around the world injected drugs - China, the United States and Russia had the largest number of such users - but there was little data from places in Africa amid concerns that a 'constellation of risk factors' exists there for the development of injecting drug use.
The research team say southeast Asia, eastern Europe and Latin America are areas of concern.
Dr. Mathers says the problem of HIV infection among injecting drug users, represents a major challenge to global health and there is a pressing need to understand injecting drug use in all countries.
Their review showed big differences worldwide - in Britain 0.4% of people aged 15 to 64 injected drugs, with 2.3% of them estimated to be HIV positive.
In Spain the proportion of addicts is lower at 0.31% but nearly 40% of them have HIV, which the researchers say is the highest proportion in Europe, whereas Australia and New Zealand have both maintained a very low level of HIV infection even though they have more injected drug users - only 1.5% of Australian injecting drug users are HIV positive.
The researchers attribute this to the swift introduction of needle and syringe exchange programs in the 1980s.
The researchers say the situation in Estonia is representative of the quick spread of HIV infections among drug users in recent years, as a decade ago HIV was not identified among people who injected but more recent estimates now suggests that the prevalence of HIV infection in some populations has reached 72%.
The study is published in the medical journal The Lancet.