A Diverse Epidemic
Since the HIV epidemic first appeared in Southeast Asia in the late 1980s, one of its leading characteristics has been its diversity-a diversity even greater than that found in Africa. Infection levels vary, from no reported infections in some countries to one per several thousand in most countries to up to 3 percent of the population in Cambodia. Why some countries in Southeast Asia have higher levels of HIV infection than others, despite the virus's introduction at around the same time, is the result of several important factors, say researchers. The nature of sex work, injection drug use, and individual mobility all play a key role in the virus's spread.

Female sex workers and their clients have been a major determinant in the heterosexual transmission of HIV in Cambodia, Myanmar, and Thailand. In 1996, prevalence rates among sex workers reached 40 percent in Cambodia, 25 percent in Myanmar, 19 percent in Thailand, but less than 1 percent in the Philippines and Vietnam.

Key contributors to the rapid and widespread transmission of HIV are the number of sexual partners per sex worker, the portion of the male population engaging in commercial sex, and the rate of regular condom use in commercial sex.

Researchers fear that even in areas where HIV infection levels are not yet high, the epidemic will eventually appear. In a survey conducted by CARE, for example, researchers found that just over half of Vietnamese men had two or more sexual partners over a two-week period and that only one-quarter of them used condoms.

In addition, HIV infection in another key population, injection drug users (IDUs), reached staggering levels in the late 1980s in Myanmar, Thailand, Vietnam, and Malaysia, reaching 60 to 90 percent within a few months. Today, 40 percent of Thailand's IDUs are infected with HIV.

Although HIV spreads rapidly among IDUs who share contaminated injection equipment, and to their sexual partners, these epidemics have so far resulted only in limited spread of HIV to the heterosexual population at large. These epidemics appear to emerge and evolve almost independently from each other, as exemplified by the two concurrent HIV epidemics in Thailand, which have been caused by two different subtypes of HIV and have had minimum crossover.

In Asia, as in Africa, mobility has been found to be another risk factor for the spread of the virus, with HIV prevalence high among people who travel widely and in areas where travel occurs. Research has found that travelers and fishermen in Thailand, for example, have higher rates of HIV prevalence than the general population. Truckers, fisherman, traders, and migrant workers who travel widely throughout the region are transmitting HIV to populations in areas where the virus was formerly unknown. High prevalence rates also appear among female sex workers, male patients in sexually transmitted disease (STD) clinics, and young males living near international borders and ports in Thailand, Myanmar, Cambodia, and Vietnam.

Lessons from Thailand
The HIV epidemic in Thailand has been more advanced than those in other Southeast Asian countries. In the mid-1980s, IDUs were the first group to be affected by AIDS in Thailand. By 1989, an explosive spread of HIV was found among sex workers, followed shortly thereafter by high rates of HIV infection in male clients and their female partners. Prevalence rates among army recruits rose to around 4 percent in 1993, while rates among pregnant women nationwide reached 2 to 3 percent in 1995.

Despite this devastating beginning, Thailand, say researchers, is now gaining control of the epidemic, especially among sex workers and their clients. According to Donald Burke, an infectious disease specialist at Johns Hopkins University who spent many years in Thailand tracking HIV, the country's epidemic has plateaued, due, in large part, to Thailand's already progressive outlook on safer sex practices. "This was a country ready to respond," says Burke.

When HIV prevalence rates began increasing dramatically in Thailand in the early 1990s, the Ministry of Public Health instituted a 100-percent condom campaign-a program to promote safer sexual practices in all commercial sex establishments. This quick response resulted in a significant drop in HIV prevalence among sex workers, from 30 percent in 1993 to 18 percent in 1995. Military recruits saw a fivefold decline in HIV infection and a tenfold decline in STDs between 1991 and 1993.

"Thai officials succeeded because of their willingness to do the studies among commercial sex workers, women, and military recruits," says Burke. "They were also extremely enlightened in their candor. They were willing to talk about the results and engage in public discourse about the best way to move forward. It's a singular success in the history of public health. They responded to a devastating epidemic that could have been much worse."

By contrast, in Cambodia, where there are high numbers of sexual partners, a high mobility rate, and low condom use, warnings by health officials of an impending epidemic were not heeded. As a result, in the early 1990s, HIV spread rapidly. Already 2 to 3 percent of the 15- to 49-year-old population is infected.

Emerging Epidemics
Whether widespread HIV epidemics will occur in countries that have, until now, displayed low rates of HIV remains uncertain. The information needed to quantify this risk, say health officials, requires information they do not possess. In most countries, for example, validated estimates of the numbers of sex workers do not exist. Without this kind of information, HIV projection models are of little value.

In some instances, religious and political considerations are thwarting prevention efforts. In Indonesia, for example, despite evidence of high rates of people with STDs and HIV infection, the Islamic nation does not recognize the country's significant sex industry or the existence of a homosexual community.

In Myanmar, the country's political unrest overrides its need for aggressive health interventions. In 1997, the Myanmar government spent less than $1 million combating HIV in a population of 42 million. By contrast, that same year, in Thailand, where more than 58 million people live, the government budgeted $90 million toward its HIV prevention campaign.

In Malaysia, the Ministry of Health responded early in the epidemic, says Rokiah Ismail, an infectious disease specialist at the University of Malaya in Kuala Lumpur. Yet the number of new infections is still increasing. "Either the programs have not been effective or they are not reaching the target groups," says Ismail.

What is needed, says Ismail, who also cites cultural and religious restrictions as a barrier to successful curtailment of the epidemic, are "more effective and intensive health education programs, outreach programs by non-governmental organizations, and peer education at the grassroots level, in villages and remote parts of the country."

While researchers cannot predict with certainty what will happen in these countries, experience suggests that sudden and sharp increases in HIV incidence will continue to occur in Southeast Asia.

"Certainly the two driving forces-sex work and injecting drug use-are there," says Francine McCutchen, an infectious disease specialist at the Henry M. Jackson Foundation Research Laboratory. "Once HIV enters the correct social network, it's just a matter of time. A country may look like it has a quiet, low level epidemic, but once the virus reaches certain groups in the population, it's only a matter of time."

"We don't have enough good data to know what the level of explosion will be, though it's fair to say that in some Southeast Asian countries, it's already well past the explosion stage," says Burke. "Yet we can do little more than encourage public health officials in these countries to make it known that it's necessary to influence political change. An organized international effort is desperately needed, but countries such as Cambodia, Myanmar, and Vietnam are not as open to international exchange as Thailand has been."