It's All In The Numbers

by Sharon J. Proctor, PhD
illustration Aaron Bihari

Tracking survival rates of people with HIV

Most of us are alive today because of one or more medical miracles. Thanks to antibiotics, vaccines, surgery, pacemakers, and other advances of the past 30 years, our lifespan is longer and quality of life far better than anything our forebears experienced a century ago. Among the medical breakthroughs in recent years are HIV drugs developed to prevent the onset of AIDS. Thanks to them, patients with HIV are surviving longer and longer. SFU’s Robert Hogg has the numbers to prove it.

A demographer in SFU’s Faculty of Health Sciences, Hogg was one of several experts who examined data collected on thousands of HIV patients in western Europe, the U.S., and Canada. Each was receiving so-called “combination antiretroviral drug” therapy. The results were published in the July 2008 issue of The Lancet, a prestigious medical research journal. The bottom line: we’ve come a long way in our fight against HIV, but we still have a ways to go.

Demography is a branch of anthropology and sociology that examines the statistics of human populations. In other words, demographers study the “big picture,” which can reveal important changes, causes, and influences. And they’re the ones who feed the news reports on trends in family incomes, births, deaths, diseases, voting, purchasing habits, and other factors in our lives. Hogg’s focus is disease trends. “I’m interested in why diseases occur. I like to link numbers with theory.” (He works mainly with Excel.)

In the Lancet article, Hogg and his colleagues describe how they pooled the results of 14 research projects in 10 developed countries. The actual data was collected by some 500 researchers, physicians, and data managers who treated and tested over 43,300 male and female HIV patients. Patients’ ages ranged from 16 to 64 and older and initiated therapy in various locations in Europe and North America from 1996 onward.

In the Lancet article, Hogg and his colleagues describe how they pooled the results of 14 research projects in 10 developed countries.

HIV (which causes AIDS) is called a “retrovirus” (“reverse virus”) – thus the term “antiretroviral drug.” Why “retro”? The answer lies in how the virus works. Human genes are made of DNA. They build RNA molecules in their own image, and it’s these RNA molecules that create the enzymes and other proteins that keep us alive. So in us, DNA creates RNA. With HIV it’s the reverse: HIV genes are made of RNA, not DNA. When the virus enters a human cell, the viral RNA creates viral DNA in its own image (the “retro” or “reverse” part). Then the new viral DNA is spliced into the cell’s human DNA. Not only is the altered human DNA inherited by succeeding generations of daughter cells, but it can produce HIV generation after generation.

There are currently some 20 approved anti-HIV drugs. According to Hogg, “Different drugs attack different parts of the virus’s life cycle. Some stop the virus from entering human cells. Some keep the viral RNA from producing viral DNA. Others keep the virus from altering human DNA. And still others attack the virus’s protein-binding ability.” He reminds us, however, that no single drug is totally effective. That’s why doctors prescribe at least two different types of drugs at a time, hitting the virus on different fronts. How successful is this approach overall? That was the point of the published study – to answer this question.

The international study demonstrated that in high-income countries, combination antiretroviral drug therapy (i.e., three or more drugs taken at once from at least two different classes of drugs) is a step in the right direction, but it isn’t a cure. For instance, in HIV patients 20 years old there was a gain in life expectancy of 13 years. That is, they lived 13 years longer than they would have if left untreated. Women receiving anti-HIV drugs had lower mortality rates and somewhat higher life expectancies than did men. Patients who were injecting illicit drugs had higher mortality rates and lower life expectancy than those who weren’t.

“A similar collaborative study that examines the life expectancy of HIV patients in low-income countries is needed,” says Hogg. Like the earlier one, it would combine demographic data from different studies, this time in Africa and other locations. “It’s hard to implement widespread HIV-drug treatment in low-income countries. A major problem is that mainly off-patent (generic) drugs are available in these countries.” Their patents having expired, such drugs are naturally much cheaper to buy than the more modern ones, and because they are few in number they limit future options for patients in these countries.

The fact is, once you get HIV you have to take three or more drugs every day for the rest of your life. Happily these drugs can reduce your viral load to the point where it’s no longer detectable. This, in turn, lowers the rate of HIV transmission to other people. “However, if a patient stops taking the drugs,” explains Hogg, “the virus will return.”

Why can’t these drugs stop HIV totally?

The answer lies in the fact that HIV patients have both free-floating and “latent” (hidden) HIV particles. The drugs attack only the free-floating ones. They miss the others, which lie dormant in “reservoirs” in tissues in the brain, intestine, lymph glands, bone marrow, and/or reproductive tract. Should the drug regimen cease, they re-emerge and multiply.

The fact is, once you get HIV you have to take three or more drugs every day for the rest of your life. Happily these drugs can reduce your viral load to the point where it’s no longer detectable.

Hogg became interested in demography while at the University of Victoria. “I was an undergraduate in anthropology and one of my professors was a demographer. I did my master’s at UVic under him.” For his PhD he went to Australian National University and worked under noted Australian demographer Alan Gray. “My thesis research was on Australian Aborigines. They have high death rates in middle age, usually from coronary heart disease. Comparing them with other human groups, I found that their mortality pattern and lifestyle risk factors differed from those of other populations.”

Right now Robert Hogg is the principal investigator in a Canadian study of 5,000 Canadian HIV patients. “We’ve so far enrolled 3,000 people in B.C., Ontario, and Quebec, and we hope to have 5,000 soon. We’ll be exploring national trends in antiretroviral therapy usage, comparing different regions of the country. We’ll examine social and behavioural differences between regions, and differences in how drugs are used. We spend so much money on drugs, but know very little about their effectiveness. We’ll be assessing this – then sharing our conclusions with provincial health-care systems and local communities.”.

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