EPIDEMIOLOGY OF HIV INFECTION
Global HIV Estimates: HIV remains a global health problem of unprecedented dimensions. Despite prevention efforts, the HIV/AIDS pandemic continues to expand globally at the rate of 13,000 new infections per day and shows no sign of slowing down particularly in low and middle income countries, where about 95% of infected persons live .
According to the World Health Organization (WHO) and the Joint United Nations Programme on HIV/AIDS (UNAIDS), a total of 33.4 million people, including 2.1 million children were estimated to be living with HIV/AIDS through the end of 2008, with a prevalence threefold higher than 1990 (Table I).
As regards new infections, they reached more than 2.7 million in 2008 with 430,000 children less than 15 years. HIV-related deaths were 2 million.
HIV is among the leading causes of death worldwide and it causes more deaths than any other infectious disease. Around 95% of HIV infected people live in non industrialized countries with not sufficient financial resources to deal with the HIV/AIDS epidemic. It is estimated that the vast majority of AIDS deaths are due to inadequate access to HIV prevention and treatment (Knight et al., 1990).
Heterosexual transmission is now the dominant mode of transmission and accounts for more than two-third of all HIV infections worldwide, although transmission in IDU (injecting drug users) and MSM (men who have sex with men) constitute a significant fraction of infections (10% and 5-10%, respectively) (Tang and Kaslow, 2003). Mother-to-child transmission of HIV continues to occur at significant rates in the developing world, accounting for roughly 400,000 new infections annually.
Transmission through injection drug use appears to play a major role of HIV epidemics in several region of the world, particularly Eastern Europe and Asia. In developed countries, the interplay between increased high risk sexual behavior and injecting drug use fuels HIV epidemics.
The global epidemic is not homogenous within regions. Sub-Saharan Africa remains the region most heavily affected by HIV infection: home to just over 10% of the world population, it accounts for more than two thirds (22.7 million) of the global number of infected people and for 72% (1.4 million) of all AIDS deaths (Zhu et al., 1993).
Moreover, 90% of all children affected worldwide live in that region. Within the region, South-Africa is the worst affected country, with more than 5.7 million people living with HIV. The leading mode of HIV transmission in Sub-Saharan Africa is through heterosexual route (Zhu et al., 1993).
Asia is becoming the epicentre of second largest epidemic with 350,000 new infections annually and an estimated 4.7 million people living with HIV at the end of 2008. In Central Asia and in countries of the former Soviet Union, the HIV epidemic has increased faster between 2000 and 2006 (20-fold increase) than in any other area of the world, reaching an estimated 1.5 million HIV cases at the end of 2008.
The vast majority of them were found among people below the age of 30 years (by comparison, in Western Europe some 30% of people with HIV fall in that age group). HIV epidemic in the region is driven by injecting drug use and increasingly by heterosexual transmission (Muciaccia et al., 2005).
An estimated 2.3 million people are living with HIV in North America and in Western and Central Europe. In high-income countries, where the great majority of people who need antiretroviral treatment have access to it, people living with HIV are surviving longer than infected people elsewhere (1).
In the United States, throughout the 1980s, the number of new AIDS cases increased rapidly. With the advent of HAART in 1995, there was a steep decline in the number of new AIDS cases and deaths. Since 2000, however the decline in the number of persons who progress to AIDS each year has leveled off.
Currently, an estimated 1.1 million individuals in the United States are living with HIV infection, one-fifth of whom are unaware of their infection and thus, miss the opportunity to receive life-saving antiretroviral therapy (9,10).
Despite the substantial reductions in deaths and AIDS diagnoses since the mid 1990s, the US epidemic continues, with an estimated 50,000 new HIV infections occurring each year, many of which occur in MSM and ethnic minority populations.
The largest proportion of newly diagnosed HIV cases was among homosexual males (almost half cases), followed by infections due to high-risk heterosexual contact (about 30%), to injection drug use (22%) and due to a combination of homosexual transmission and injection drug use (5%) (Berlier et al., 2005).
In Latin America, an estimated 170,000 new HIV infections occurred in the 2008, bringing the number of people living with HIV to an estimated 2 million (Clevestig et al., 2005). HIV trends in Latin America have also been relatively stable in the past decade, with most transmission attributed to MSM and heterosexual intercourses.