Using public health surveillance data, investigators led by Chi-Tai Fang and Jung-Der Wang of National Taiwan University evaluated how cost-free provision of an anti-HIV regimen known as highly active antiretroviral therapy (HAART) affected the evolution of the HIV epidemic in Taiwan. Previous research has shown that HAART, which suppresses the level of HIV, prolongs the survival of HIV-infected individuals and reduces rates of mother-to-child and heterosexual transmission of the virus. In the current study, Dr. Fang and colleagues investigated whether widespread use of HAART could reduce the rate of HIV transmission in an entire population.
The investigators noted that although attempts to study this question have been complicated by the high cost of HAART and the difficulty of identifying individuals with early, asymptomatic HIV infection through national surveillance, Taiwan is a setting well-suited to address the question. Like many other countries, Taiwan has been affected by the HIV epidemic since the mid-1980s. Beginning in 1989, the government established a nationwide HIV surveillance system. For example, all men are tested at 20 years of age as part of mandatory military service. Beginning in April 1997, the government adopted a policy to provide all HIV-infected citizens requiring therapy with free access to HAART through its national health insurance program.
Dr. Fang and colleagues conducted an observational study of the available HIV surveillance data in Taiwan using mathematical modeling and statistical analysis. They used an exponential model of the evolution of an HIV epidemic to estimate the transmission rate before the implementation of the free-HAART policy (January 1990 to April 1997) and after the policy was enacted (May 1997 to December 2002). The validity of their model, they pointed out, depends on several assumptions, including a low HIV prevalence in the country. They found that the estimated average HIV transmission rate was 0.391 new cases per prevalent case-year in the pre-HAART period and 0.184 new cases per prevalent case-year afterwards. Thus, their model indicated that the estimated HIV transmission rate decreased by 53% after the government implemented its free-HAART policy.
A limitation of this type of observational study, the researchers noted, is that any conclusion about a causal link (i.e., that the free-HAART policy caused the decrease in HIV transmission) must be examined to exclude the influence of potential confounding factors. A major confounding factor in this study, they said, was behavior patterns; a decrease in high-risk sexual behavior, for example, might be an alternate explanation for the decrease in HIV transmission.
To control for this factor, the researchers used the incidence of syphilis, which is also tracked in Taiwan by nationwide surveillance, as a marker for trends in sexual behavior. If there were indeed a decrease in unprotected sex, there should be a corresponding decrease in syphilis incidence. After analyzing the surveillance data on syphilis, they found there was no significant change in reported syphilis cases among the general population from 1993 through 2002, and no significant difference in the incidence of syphilis among HIV-infected individuals in the periods before and after the free-HAART policy was implemented. According to the authors, the syphilis results indicate that the decrease in HIV transmission is unlikely to have been caused by a decrease in high-risk sexual behavior.
"Our results make a strong case for the widespread use of HAART to control HIV epidemics in countries with low HIV prevalence," Dr. Fang said, "and should be of interest to health authorities around the world." He cautioned, however, that their results may not apply in a high-prevalence country with a mature epidemic. A free-HAART policy may not be feasible in such countries due to the high cost of the drug regimens, or may not significantly or quickly change the prevalence of HIV infection because of the long survival of individuals infected with HIV prior to initiation of the policy. The investigators also cautioned that a free-HAART policy alone cannot eradicate an HIV epidemic in any country and should be accompanied by other measures, such as public education about safer sex and condom use.
Founded in 1904, The Journal of Infectious Diseases is the premier publication in the Western Hemisphere for original research on the pathogenesis, diagnosis, and treatment of infectious diseases; on the microbes that cause them; and on disorders of host immune mechanisms. Articles in JID include research results from microbiology, immunology, epidemiology, and related disciplines. It is published under the auspices of the Infectious Diseases Society of America (IDSA). Based in Alexandria, Va., IDSA is a professional society representing more than 7,500 physicians and scientists who specialize in infectious diseases. Nested within the IDSA, the HIV Medicine Association (HIVMA) is the professional home for more than 2,600 physicians, scientists and other health care professionals dedicated to the field of HIV/AIDS. HIVMA promotes quality in HIV care and advocates policies that ensure a comprehensive and humane response to the AIDS pandemic informed by science and social justice.
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