(AP) -- Fewer Zimbabweans are getting infected with AIDS, and researchers speculate it's due in part to a battered economy that's leaving men short of money to be sugar daddies and keep mistresses.
Presenting a study of the infection rate among pregnant women at a major international AIDS conference in South Africa this week, Dr. Michael Silverman said the prevalence of the virus that causes AIDS fell from 23 percent in 2001 to 11 percent at the end of 2008. His study was based on tests of 18,746 women at a prenatal clinic in rural Zimbabwe over that period.
Silverman, a Canadian infectious disease expert, works at Howard Hospital in Zimbabwe, where the women were tested.
Silverman said he concluded that "a lot of the effect (of the decline in HIV infections) is from the collapsing economy." AIDS experts have long noted that the richest countries in Africa are also those with the highest infection rates.
"You can't pay the sex worker if you have no currency," he said. "It's hard to have a concurrent relationship if you're always in earshot of your spouse, because you can't afford to travel. Because of the economic collapse, people are forced to stay home, like being in quarantine."
Getting accurate AIDS numbers in Africa, however, has been notoriously difficult since researchers are often forced to guess from imperfect indicators like HIV incidence in pregnant women, instead of counting actual numbers of HIV patients.
Researchers long have speculated how much they could drive down incidence of AIDS if people were constricted to having sex with partners in their age group. Now, in Zimbabwe, said David Katzenstein, a professor of infectious diseases at California's Stanford University who has worked in Zimbabwe for 25 years, "everybody's hungry, there aren't as many sugar daddies (older men who attract young girlfriends with gifts and money) and those that are around don't have as much sugar."
"The good news from Zimbabwe is that, apparently without any intervention whatsoever, there does seem to be a declining incidence in young women and maybe young men," said Katzenstein, who was not involved with Silverman's study.
"Lack of transport, lack of money, lack of food, all decrease the amount of sex that you can have and the number of partners," Katzenstein said.
Katzenstein noted there is no evidence of a decline in infection rates in other places which had incidences as high as Zimbabwe - Swaziland, Botswana and South Africa's KwaZulu-Natal province. AIDS infections in many African countries are tending toward a plateau.
But Mike Chirenje, an AIDS researcher in charge of obstetrics and gynecology at the University of Zimbabwe, said: "You're also talking about a period of time when a lot of people were not accessing ARV (anti-retroviral) therapy. So you cannot rule out cases of people dying for lack of access to ARVs" and therefore not being around to be studied.
Another consideration: Women infected with the virus are less likely to fall pregnant.
Many ask how anyone can really know what is going on in Zimbabwe, where President Robert Mugabe's yearslong fight to remain in political power triggered economic and social crises that caused as much as a third of the population to flee, collapsed government health and education and left more than 80 percent jobless. The collapse of piped water services brought on a cholera epidemic that killed 2,000 people.
But Howard Hospital, run by the Canadian branch of the Salvation Army, remained open throughout the crises.
The decline registered by Silverman at Howard is "in keeping with national data that shows from research 10 years ago a decrease from 30 percent (prevalence) to 15 percent today," said Chirenje, whose work is funded in part by the U.S. National Institutes for Health and who has done clinical trials, especially in HIV prevention through microbicides and risk reduction through condom use.
Simon Gregson, a professor at Imperial College London and a demographer and epidemiologist who has worked half time in Zimbabwe since 1998, said he also sees a sharp decline in Zimbabwe. He was not involved with Silverman's study.
Through studies following the same 10,000 to 12,000 people every couple of years, Gregson said: "We have found that it is not just that more people are dying than are becoming newly infected; it's not just because the death rate is very high; but the rate of new infections have been coming down and that is because people have been changing their behavior and adopting safe practices."
The studies show people, particularly men, are having fewer partners, and condom use is quite high, Gregson said in an interview from his office in Zimbabwe.
"What's not so clear is what caused them to change their behavior and why there is more of a change in Zimbabwe than in other neighboring countries."
Chirenje also said that behavior change appeared to be mainly among men. Studies from his research unit at primary health care centers have women reporting no changes in the frequency of their sexual activity of three or four times a week, he said.
Chirenje estimated that between 30 and 40 percent of Zimbabweans eligible for ARV therapy are receiving it. Katzenstein said only about 100,000 are receiving therapy - one-tenth of those believed infected and much fewer than the 250,000 who should be getting treatment. He said an estimated 50,000 Zimbabweans are dying of AIDS each year.
©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Explore further: Animal study provides first evidence that gel can prevent multiple virus transmission in vagina/rectum