Introduction

Twenty years into the HIV/AIDS epidemic, much is known about preventing HIV infection. Yet the epidemic continues and is in fact unrelenting in some places. Worldwide, surveillance and prevention responses vary as a result of many factors.

This article cannot provide a full description of all aspects of the epidemic in every country or the vast and diverse range of cultural, social, environmental, biological, and even political dynamics of this devastating epidemic. Instead, this article will provide a snapshot of some of that diversity and range by describing the epidemiology (i.e., frequency, distribution, and behavior) of HIV in a few representative regions and countries.

The HIV/AIDS epidemic is fraught with paradox and true drama: life-saving treatments bring hope as well as risk; countries that share borders have vastly different epidemics. HIV has changed the world and is still changing it.

Antiretroviral Therapies Significantly Impact Mortality

The numbers of new AIDS cases and AIDS deaths are both falling significantly in countries that provide antiretroviral therapy for a majority of those diagnosed with HIV. However, there is no sign that new HIV infections are following the same downward course. On the contrary, extremely worrying recent evidence suggests that the advent of life-prolonging therapies may have led to complacency among some groups of people about the dangers of HIV, and that that complacency may be leading to rises in risky behavior.

For the past several years in San Francisco, for example, there have been decreases in the number of men who have sex with men (MSM) reporting consistent condom use, increases in the number of men reporting unprotected anal sex with multiple partners, and increases in rectal gonorrhea. Many of the men sampled in these studies reported that they did not know their partners' HIV status. Of particular concern is that the absolute number of HIV positive people is probably growing because of improved survival.

Theoretically, antiretroviral therapy could reduce a person's infectiousness, or the likelihood that an infected person might pass on the virus to a sexual partner. Evidence of this effect is not conclusive, but some new research has demonstrated reduced transmission in a study of serodiscordant heterosexual couples (i.e., those in which only one partner is HIV positive). On the other hand, even if a person's overall infectiousness is reduced by anti-HIV drugs, there is good evidence that viable virus (i.e., virus capable of reproducing) can be recovered from seminal fluid in men taking highly active antiretroviral therapy, or HAART.

Yet until further studies of HIV treatment and infectivity are done, it must be assumed that a higher level of HIV in the pool of potential sexual partners means a higher risk of transmission whenever unprotected sex occurs with a partner of unknown HIV status. More than ever, prevention leaders, community-based organizations, and public health officials must continue to pursue effective HIV prevention efforts in communities where HIV incidence (number of new infections) has declined and prevalence (infection levels) is stable or increasing.