QUICK FACTS
Mathematical statistician Glen Satten is using the IMSL Fortran Numerical
Libraries to model the natural history of the human immunodeficiency
virus type 1 (HIV-1). Dr. Satten is associated with several projects
at the CDC's Division of HIV/AIDS, where he is working to elucidate
the course of this complicated disease.
THE PROBLEM
HIV is an epidemic with varying methods of transmission accounting
for its spread worldwide. Heterosexual contact is the primary source
of HIV transmission in Africa, and the major HIV transmission mode
in Asia, which accounts for 60% of the world's population.
"Homosexual transmission and shared needles among injecting
drug users are still the primary sources of transmission in North
America, but the proportion of new AIDS cases accounted for by heterosexual
transmission is increasing steadily," Satten said. A unique
study group of male military inductees in Thailand provided an opportunity
for Dr. Satten and his colleagues to develop models of the probability
of female-to-male HIV transmission per sexual contact.
The analysis was possible because the situation in Thailand allowed
for the assumption that HIV-1 men in the study had been infected
through sex with female prostitutes since 1988. "The Thai study
group is unique because we can determine how and when the HIV was
most likely transmitted, then chart the infection from its onset
and continue as it progresses through stages," said Satten.
"Identifying the stages of HIV development will assist in treatment
of the infection."
While prostitution in Thailand is not legal, it is socially accepted.
The military inductees provided information on their frequency of
contacts with prostitutes, which would be difficult to obtain in
other settings. In addition, the Thai Ministry of Public Health
has been monitoring the increase of HIV among female prostitutes
since mid-1989, when the prevalence was 3.2%. By mid-1992, the prevalence
had increased to 23%.
THE SOLUTION
"The Thai study is unique because we know the mode of transmission
can determine the number of contacts of which transmission could
have occurred, but most important because these contacts occurred
with people who were likely to be recently infected, since widespread
transmission of HIV in Thailand was a fairly recent phenomenon at
the time the study was conducted. Our study supports the hypothesis
that individuals who are recently infected are themselves more infectious,"
said Satten.
A Fortran programmer, Dr. Satten first used the IMSL Libraries
during postdoctoral work in biostatistics at the University of North
Carolina at Chapel Hill in 1988. Models he develops at the CDC rely
primarily on the optimization routines in the IMSL Libraries to
estimate the values of parameters that best describe the observed
data, which are called maximum likelihood estimates. The CDC relies
primarily on an IBM mainframe and PCs, although Dr. Satten has recently
received authorization to obtain a DEC® Alpha 3000-600 workstation
to run both the IMSL Fortran Numerical Libraries and IMSL Exponent
Graphics software. Increased speed is the primary reason for his
move to a UNIX®-based system.
RETURN ON INVESTMENT
"I use the IMSL Libraries to reduce my program development
time so that I can concentrate on those aspects of a problem that
are novel and require statistical or AIDS-related expertise,"
says Satten. The IMSL Libraries were used to model the data, and
the findings were presented to researchers at the IX International
Conference on AIDS in June 1993 in Berlin. A mathematical model
was developed to estimate the probability of HIV-1 transmission
per sexual contact. Data included the inductee's age at first sexual
contact, frequency of sex with female prostitutes, province of origin
and province-specific HIV-1 seroprevalence among prostitutes.
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