Since last November’s report that the relationship between
viral load and disease progression in women may not be the same as in men,
clinicians and activists have been questioning whether women should be
encouraged to start treatment at lower viral loads than men.
Rates of disease progression at different viral load and CD4
levels were first calculated after an analysis of the MACS cohort of gay men, a
group followed since 1982. These findings formed the basis for US and
international guidelines on when to start treatment.
Homayoon Farzedegan and colleagues at Johns Hopkins School
of Public Health (The Lancet Nov 7 1998 href="http://www.thelancet.com">http://www.thelancet.com
had a 60% higher risk of developing AIDS than men at the same viral load level.
The study looked at viral load differences between 527 male and female injecting
drug users tested in 1988 and 285 tested in 1993. The average follow-up was
almost six years. In other words, women with viral load of 20,000 copies were
1.6 fold more likely to develop AIDS in the follow-up period than men with
similar viral load.
Subsequently, colleagues at Johns Hopkins University School
of Medicine (The Lancet February 6 1999 href="http://www.thelancet.com">http://www.thelancet.com
found no difference between men and women in viral load and rates of disease
progression.
Now, several other research groups have looked into disease
progression rates amongst their own patients. Swiss and Italian researchers have
failed to find any difference between men and women. The Swiss HIV Cohort Study
looked at 1337 men and women, and found no difference in viral load levels at a
range of CD4 counts, nor any difference in the risk of developing AIDS during
the follow up period. In the Italian ICONA cohort, men and women had similar
viral load levels when they were matched according to their CD4 counts, unlike
in the Farzedegan study. The ICONA study reported on 2011 men and women (The
Lancet, February 13 1999 href="http://www.thelancet.com">http://www.thelancet.com
Explanations for the discrepancy spotted by Johns Hopkins
School of Public Health are far from clear. Hormonal difference have been
suggested, but a study by University College School of Medicine in 1995 found
that HIV-negative women patients in a GUM clinic had higher CD4 counts than men
(an average of 111 cells higher). In the Johns Hopkins study however, women had
lower CD4 counts than men at equivalent viral load levels.
Another suggestion is that active use of cocaine amongst
male members of the cohort may have boosted viral replication without affecting
the rate of disease progression. Such differences have not been detected in
other studies which have set out to look for any effect of active drug use on
disease progression.