The highest rates of HIV infection in populations have been seen in sub-Saharan Africa, where approximately 25 million people living with the disease can be found, and where heterosexual transmission is the main form of spread (UNAIDS, 2005). However, with the exception of this region, there is mounting evidence that a principal mode of transmission of HIV in many regions is through the sharing of needles in IDU (Aceijas et al., 2004). Globally, there are over 13 million injection drug users, with 25 countries having documented an HIV seroprevalence of over 20 percent among this group. The striking causal association between increasing IDU and the spread of HIV has been documented in many developed nations, such as the US, Canada, and Western Europe. Now, though, this route of exposure has taken the virus into regions spared in the early decades of AIDS - places like Central Asia and the Balkans, and remote regions far from capital cities, such as the far western province of Xinjiang in China, and Irkutsk in Russian Siberia, which now have some of the highest HIV rates among injection drug users reported for these large countries.

In the former Soviet Union, estimates range from 50 to 90 percent of HIV incidence being attributable to injection drug use (Rhodes et al, 1999c). Before 1990, many states of the former Soviet Union had been largely spared from the HIV/AIDS pandemic, due in part to tight restrictions on population movement and contact with foreigners (Field, 2004). There was little evidence of spread of

HIV among injection drug users in the former Soviet Union in studies completed in 1995 (Rhodes et al, 1999a). Since then, many countries have demonstrated rates of spread of the disease that are best described as explosive (Rhodes et al, 1999a). A study completed with injection drug users in Togliatti City in Russia demonstrated a seroprevalence of 56 percent, with three-quarters of seropositive users being unaware of their status. This is in stark contrast to the situation in Togliatti City a few years earlier, when the prevalence of HIV was essentially zero (Rhodes et al, 2002). This study demonstrates well a common theme of how quickly HIV can spread when the virus is introduced into a previously isolated population with established high-risk behaviors. Similar patterns have been seen in multiple states of the former Soviet Union, with the highest seroprevalence rates found in the Ukraine, Russia, and Belarus.

Explosive spread of HIV was also demonstrated in injection drug users in Bangkok, Thailand, when HIV seroprevalence increased from 1 percent to 40 percent within the single year of 1988 (Vanichseni et al, 2004; see also Figure 3.3). Northern Thailand borders the Golden Triangle and, due to decreased availability of opium secondary to poppy eradication efforts, larger populations have turned to parenteral use of heroin - with its associated harmful health consequences - as a substitute (Gray, 1998). A cross-sectional study looking at associations between risk factors and HIV seroprevalence was completed in this region of Thailand on 1865 patients admitted for drug detoxification in one of the region's drug treatment centers. There, HIV prevalence in injection drug users was 30 percent (154/513), compared with 2.8 percent (33/1180) in non-users - an increased

• Thanyark Hospital for Drug Treatment, MOPH. O Bangkok Metropolitan Drug Treatment Clinics.

• Median Provincial National Sentinel Surveys, MOPH.

• Thanyark Hospital for Drug Treatment, MOPH. O Bangkok Metropolitan Drug Treatment Clinics.

• Median Provincial National Sentinel Surveys, MOPH.

Figure 3.3 HIV infection rates among IV drug users in Bangkok, and national median rates, 1985-1991.

risk of 14.8 times (95 percent CI, 10.2-21.6) (Razak et al, 2003). In Thailand, control measures have largely focused on aggressive HIV/STD-risk education and enhancing provision of services, with the emphasis on sexual transmission. While measures including education and the "100 percent condom program" have mitigated the epidemic among the general population, there has been little effect on the epidemic among injection drug users (Beyrer et al., 2003). The data from Thailand provide an excellent representation of the concept that HIV cannot be eradicated simply by directing prevention strategies at sexual transmission, as a large reservoir of disease remains among injection drug users.

Historians have speculated that sexually transmitted infections were first introduced to China by Portuguese traders in the sixteenth century, and the diseases were well established when Mao Zedong came to power (Cohen et al., 1996). Maoist policies included very restrictive and heavily enforced prevention strategies and treatment, resulting in virtual eradication of the then prevalent STDs within a decade. However, with China's entrance to global markets in the 1980s there was a sharp increase in the prevalence of STD, associated primarily with commercial sex work (Zhang and Ma, 2002). Sporadic cases of HIV were also reported, but there was little evidence of epidemic spread of HIV in China until 1989. That year, there were reports of HIV infection among 146 drug users in the Yunnan province (Zhang et al., 2002). Yunnan province is situated along the borders of Burma and Laos, collectively called the "Golden Triangle" and known to be responsible for approximately 60 percent of worldwide heroin production in 1990 (Beyrer et al., 2000). Since that time, HIV infection has spread to all 31 provinces, with drug users making up 60-70 percent of the incidence (Portsmouth et al., 2003). A recent cross-sectional study was completed in Chengdu, a city of 11 million in the Southwest, which is in close proximity to major heroin supply and trafficking areas. Earlier reports had demonstrated high-risk behavior among drug users including a high prevalence of injection behavior, extensive sharing of syringes, and an already high HIV seroprevalence among injection drug users (Wu et al., 2004). In the current study of 266 users, sharing of injection materials was recorded in 39 percent (103/266), and such behavior was associated with being an ethnic minority or "internal migrant" (P < 0.05) (Chamla et al., 2006). Another recent study evaluated indicators of high-risk behaviors among 1153 users in China, and found that a higher prevalence of sharing needles and unprotected sex was also most associated with being a temporary migrant (P < 0.01) or an ethnic minority (P < 0.05) (Yang et al., 2005). These studies demonstrate that even within the population of injection drug users, there are sub-populations exhibiting higher-risk behaviors that further propagate the virus. What's more, the data reveal a common association of IDU and high-risk sexual behaviors, which functions to bridge this epidemic with the population as a whole.

Iran, a predominantly Muslim country situated in the Middle East, is experiencing an HIV epidemic predominantly within its injection drug user population (UNAIDS, 2005). Although there have been only 6700 reported cases of HIV/AIDS in Iran, of which about 85 percent are injection drug users and 10 percent secondary to sexual contact - it is estimated that there are closer to 30,000 people living with the disease (Razzaghi et al., 2006). Iran is bordered by Afghanistan, which is known to produce a large proportion of the world's opium supply (see Figure 3.4). Opium is extensively trafficked from Afghanistan through Iran and, similar to the regions of China proximate to the Golden Triangle, there are exceptionally high numbers of injection drug users in this region (UNODC, 2005). A recent cross-sectional prevalence study was completed with 611 imprisoned drug users; both injecting and non-injecting. Among non-injectors, the HIV seroprevalence was 5.4 percent (21/390); the only statistically significant risk factor for HIV was having had sex but not used a condom (aOR 3.42; 95 percent CI, 1.25-9.36). The HIV seroprevalence was 15.2 percent (25/165) in injectors; the main risk factor was having shared injection materials while incarcerated (aOR 12.37; 95 percent CI, 2.94-51.97) (Zamani et al, 2005). These results indicate an increased risk of HIV in drug users from injection. Among the non-injectors, increased risk was secondary to high-risk sexual behavior rather than drug use. The effects of imprisonment on high-risk drug use and spread of infectious disease will be explored in a later section of this chapter, as these study results introduce a well-established causal link.

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