Prevelance of injecting and injecting risk

This article sets out what we know about the answer to the questions - how many injectors are there in the UK? and what do we know about injecting risk?

Because of its illicit nature, injecting drug use tends to be hidden and difficult to quantify. This, plus the fact that it is relatively rare, means that the usual way of finding out how much of something is happening - i.e. surveying the population - is very unreliable.

Usually analysts instead work from what we do know (such as numbers of drug users who have tested positive for HIV, or numbers in treatment) and extrapolate to the number of injectors from this. Estimates differ depending on the starting point and the assumptions made about how the number you're starting with relates to the number of injectors.

It is therefore impossible to give a definitive figure of the number of injectors in the UK. Different figures will also be obtained depending on whether prevalence is defined as people who have injected in the last month, year, five years, or in their lifetime.

In 1992 it was estimated that 100,000 people in England and Wales had injected in the previous five years and 175,000 had injected in their lifetime.

In the year 2000 a Home Office research report described different studies that had estimated that in England and Wales between 225,000 to 405,000 people had injected drugs in class A of the Misuse of Drugs Act (heroin, cocaine, amphetamines), the median estimates were 270,000 and 159,000 respectively. It was thought that of these 'lifetime ever' injectors 133,000 and 239,000 were currently injecting. In Scotland another 30,000 people may have injected at some time in their lives and 23,000 people may have done so in the year 2000.

There has been increased access to treatment since 2000, and there hasn't been a notable increase in the injecting of class A drugs, so number of current injectors in the UK is therefore probably around 150,000.

All national estimates will mask wide regional variations. Per head, there are estimated to be four times more problem drug users in some parts of the UK than in others. At least as great a variation in injecting can be expected.

At a local level it becomes feasible to use the ‘capture recapture’ method to estimate the injecting population. This is based on a widely used method for estimating the size of wild animal populations within a particular habitat. A sample of animals is captured, marked, and then released. Another group is then captured and the overall population size is worked out from the percentage of the second group that is recaptured.

This technique has been applied to drug injectors by ‘capturing’ them in two or more sets of data, for example by comparing drug agency data to police arrest, or A&E admission data. This technique has its own limitations as the samples need to be independent, and this is rarely possible. Practical guidance has been produced by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA 2001).

Prevelance of infections
Infections are common among injecting drug users. Around one-half of injecting drug users have been infected with hepatitis C, one-sixth with hepatitis B, and about one-third reported a symptom of a bacterial infection (such as a sore or abscess) at an injecting site in the past year.

The prevalence of HIV among those who have injected drugs remains low and is estimated to be 1.5% overall in the UK. However, it varies across the country from 0.6% in Scotland to 4.1% in London. The prevalence of HIV among current injectors has increased from 0.7% to 1.5% over the past decade, and is now similar to the level found in the early 1990's.(Shooting up 2010.)

There is a harm reduction works DVD which explores these issues, and describes the prevelance of blood borne viruses – you can see it by clicking here (link to the watch the film page of 'HIV, hepatitis C and injecting drug use')

The extent of risk behaviour
Underpinning continuing spread of hepatitis C infection is the continuation of behaviours capable of transmitting the virus and also of transmitting HIV should it become more common. Most worrying is a rise in the proportion of injectors interviewed at drug services or genitourinary clinics in England and Wales who admit having in the last month passed on or received used needles and syringes (Unlinked Anonymous Surveys Steering Group. 2001). Typically under 20% up to 1997, in London this doubled to over 40% in 1999 and 2000. Outside London it rose to about 30%. A similar increase remained when the focus was narrowed to newer (under four years) and younger (under 25) injectors.

This picture is replicated in a different series of statistics based on assessments made in England of new or returning clients seen at drug services or by GPs. These document a rise both in the numbers currently injecting (from 7000–9000 in the early 90s to over 13,000 by 2000–2001) and in the proportion of injectors who admit having recently shared injecting equipment (from 12–13% to 20–21% over the same period). In Scotland, too, similar statistics show the number of current injectors newly attending drug services and GPs rising from 2327 in 1996/97 to 3131 in 2000/01 and the proportion who recently shared injecting equipment increasing from 28% to 34%.

The same type of statistics show that in England and Wales recent sharing of any form of injecting equipment (including but not limited to needles and syringes) is the norm among new drug injecting clients seen at drug services or by GPs. Since the mid-90s the proportion increased by about 10% in London to 69% in 1999–2000 but was stable at around 60% in the rest of England and Wales.

Worrying as they are, official statistics based on injectors in treatment may under-estimate the extent of risk behaviour. In 1998, 1214 out-of-treatment injectors in seven English cities were interviewed. Detailed questions revealed a higher level of sharing than the brief enquiries used to generate official statistics. In the last four weeks, 78% had engaged in injection-related behaviour which might spread viral infection. Just over half had either re-used or passed on used needles and syringes and three-quarters had shared equipment such as filters and spoons.

Sharing was typically confined to two friends or partners rather than strangers. Other injecting equipment tended to be shared more frequently than needles and syringes. For example, about 1 in 7 respondents said they had frequently re-used containers, filters and water or bleach solutions, but just 5% admitted frequently passing on or re-using syringes or needles, even with sexual partners.

Answers to detailed questions put to injectors in two cities in the south west of England again suggested that official statistics underestimate risk behaviour (Bennett 2000) Respondents were recruited via NSP and drop-in services and by ‘snowballing’ from previous contacts. In the past month 40% had shared syringes/needles and 85% had shared other injecting equipment, including spoons and filters and solutions used to dissolve the drug or clean the equipment. Sharing with strangers was rare, but on nearly 1 in 5 occasions the injecting partner was described as an ‘acquaintance’ rather than a friend.

In London a sample of heroin injectors interviewed in 1994, most of whom were not in treatment, confirmed that sharing of syringes and needles was common but also that sharing of other injecting equipment such as spoons and water was twice as common (Gossop 1997). In the past year, 62% of this sample had shared equipment of some kind. Re-use of someone else’s syringe tended to be restricted to close friends and heroin injecting sexual partners, but about a quarter of the sample had re-used spoons or water after they had been used by a casual acquaintance and nearly a third had allowed these to be re-used by a casual acquaintance.

References
Modelling drug use: methods to quantify and understand hidden processes. EMCDDA 2001.

Unlinked Anonymous Surveys Steering Group. Prevalence of HIV and hepatitis infections in the United Kingdom. Annual report of the Unlinked Anonymous Prevalence Monitoring Programme 2000. Department of Health: December 2001.

Gossop M. et al. “Continuing drug risk behaviour: shared use of injecting paraphernalia among London heroin injectors.” AIDS Care: 1997.