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DPH bungles on HIV infection rate projections




 

Sensational headlines circled the globe last Friday, June 30. "S.F. HIV Rate Surges; alarming incidence of new infections raises fears of scourge to come," exclaimed the San Francisco Chronicle.

"New HIV infections soar in San Francisco," declared the Reuters new service.

"The percentage of new HIV cases in The City almost tripled from 1997 to 1999," said the Examiner.

Epidemiology oftentimes seems to be more of an art form than a science, at least in this town. And when it comes to the human immunodeficiency virus, San Francisco can seem like ground zero in the art of going out on a limb with disease forecasting.

San Francisco health officials were working overtime feeding juicy quotes and leaking unpublished data to the media last week � timed in advance of media frenzy surrounding next week's International AIDS Conference in Durban, South Africa, and also in the midst of heated negotiations in Washington, D.C. where Congress is poised to cut Ryan White CARE Act funding to San Francisco due to a dropped AIDS caseload.

The crux of the stories was that DPH had reviewed a dozen or so indicators of the HIV infection rate in the city's gay community � in particular looking at the number of men who took the HIV antibody test at anonymous test sites � and found that the rate of new infections had doubled, or even tripled, in the last few years.

DPH officials were quoted saying that the estimated number of new infections among gay and bisexual men in San Francisco had gone up from 500 to almost 900.

Now, the same officials are singing a different tune.

"The 900 number is not an official DPH number � The comparison to sub-Saharan Africa is unfortunate," Dr. Willi McFarland, an epidemiologist with DPH told the Bay Area Reporter, referring to a quote he gave to the Chronicle: "These are sub-Saharan African levels of transmission."

While all the media reports quoted local officials stating that a chief factor feeding the higher infection rate was the fact that people with AIDS are living longer, creating a large pool of infected people, who in turn are infecting others, McFarland and DPH director Mitch Katz were later both instead emphasizing other factors, including the size of the gay population itself.

"The reason why the [900] number of new infections is a less reliable data point is that it's very sensitive to estimates in the size of the population," Katz told the B.A.R. "And while I have not yet reviewed the documentation that supports the 900 new infections a year, what I do know is that part of the increase from 500 is due to a better estimate in the size of the gay male population which increases its size, and also it may be that the community itself is growing in size. Obviously the more gay men or the more people at risk in general that you have, the higher the number of new infections."

No vote was taken at a closed May 24 meeting of AIDS prevention experts in San Francisco organized by DPH and the Center for AIDS Prevention Studies of the University of California at San Francisco. The meeting was convened in preparation for a "community consensus" meeting to be held this fall.

The stated purpose of the meeting was to consider revising the estimated number of new HIV infections taking place in San Francisco each year, based on data collected from a variety of sources.

It is no secret among prevention experts in San Francisco that there has been an increase in new infections in the gay and bisexual community, and a number of factors are feeding into this, chiefly "barebacking," or unprotected anal sex, behavior likely compounded by a concurrent epidemic of "party drugs" including crystal methamphetamine in the gay community. Prevention experts also point to a perception that new combination antiviral therapies have made the disease less threatening.

Using the new detuned ELISA HIV antibody test, which helps researchers determine whether an HIV infection has occurred before or after 129 days prior to the drawing of the sample of blood, researchers applied a complicated formula to come up with their estimates of the number of new infections that were leaked to the media sources and led to last week's headlines.

In an unreferenced abstract, among thousands to be published in conjunction with the Durban conference next week, McFarland reported a 2.1 percent infection rate at anonymous test sites in 1996; a low of 1.3 percent in 1997; 2.3 percent in 1998; 3.4 percent in 1999.

None of the media reports provided the raw numbers used to come up with these annualized percentages.

In 1996, McFarland told the B.A.R., of 3,505 gay and bisexual men taking the test, there were 25 recent infections.

In 1997, of 3,114 gay and bisexual men, 14 were recently infected.

In 1998�and here's the big jump leading to all the headlines�of 3,291 taking the test, 30 were recently infected.

In 1999, there was an unexplained drop in the number of gay and bisexual men taking the test at anonymous test sites, but according to McFarland, there were 1,995 who took the test, and of these, 26 had been infected within the last 129 days.

Yet Jim Dilley, executive director of the UCSF AIDS Health Project, which operates the anonymous test sites in San Francisco under contract with DPH, noted about 9,000 people took the HIV tests in 1999. Of those, 127 tested positive, Dilley said, though some of these may have been older infections, as the detuned ELISA test was not used.

At press time, DPH researchers had failed to explain why their numbers are apparently a subset of the total number taking the test at anonymous test sites.

"It's unfortunate that it got out before we were able to say as a group that this is our best estimate of the number of new infections," said Steven Tierney, director of HIV prevention at DPH. "I do think that the number has clearly gone up."

"Obviously we feel very strongly that there is evidence that there is increased HIV incidence in San Francisco which parallels the reports of increased unsafe sex behavior which we've made previously," agreed Katz.

Some of DPH's usual critics were quick to jump on the apparently sloppy, incomplete data leaked from DPH to the major media outlets last week.

"Instead of telling the public how many HIV tests have been administered in San Francisco and the consequent number of positive, negative and indeterminate results, UCSF and the DPH have concocted an elaborate mathematical method using numerous 'indicators' and employing novel detuned ELISA tests unapproved by the Food and Drug Administration to concoct HIV increases on paper," said David Pasquarelli of ACT UP/San Francisco.

"These increases are not real and the study's methods, indicators, and testing technology have never before been employed for this purpose nor verified by researchers unaffiliated with the AIDS industry," he added.



 


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Information in this article was accurate in July 9, 2000. The state of the art may have changed since the publication date. This material is designed to support, not replace, the relationship that exists between you and your doctor. Always discuss treatment options with a doctor who specializes in treating HIV.