Bay Area Reporter - June 8, 2001
analysis by Bob Roehr

Mainstream media accounts dutifully relayed the alarmist message without looking too closely at the shaky epidemiology on which it is based. Had they done so, they might have come to the conclusion that the news conference was more about politics than about science.

CDC researcher Linda Valleroy led the team that conducted the study. She explained that while it is important to understand the prevalence of HIV, or how many people are infected with the virus, "It is even more important to understand the rate of new infections or incidence." This helps target resources to where they are most needed.

In February the CDC released "preliminary data on HIV prevalence" from the Young Men's Survey, an ongoing study since 1994 that looks at gay and bisexual men ages 23 to 29 in six cities - Baltimore, Dallas, Los Angeles, Miami, New York City, and Seattle. It showed an overall infection rate of 13 percent, with a "very high" rate of 32 percent among the African American men sampled.

The new data was the second part of that survey, conducted in 1998-2000. It used a STARHS assay to determine annual incidence of new infections. STARHS measures two different antibodies to HIV. One antibody appears about a month after infection while the second takes at least three months to develop. If only the first antibody is present, the researcher knows that the infection is relatively recent.

Valleroy said that among those they tested, the overall HIV incidence was 4.4 percent. The rate varied tremendously between groups. The rate for white gay men was 2.5 percent, for Hispanics 3.5 percent, and for African Americans 14.7 percent.

It means that for every 100 African American MSMs that they tested, 15 became infected with HIV during the last year. She called these "explosive HIV incidence rates." Valleroy said the 4.4 percent overall incidence rate is similar to that seen in southern and eastern Africa in the early 1990s, immediately prior to the rapid growth of HIV in that region to about 20 percent of the total population.

She said that American data from surveys conducted in the early 1990s indicated a 2 to 3 percent overall rate of infection among MSMs. A 4.4 percent rate is comparable to what was seen in the U.S. in the mid-1980s at the peak of new infections. There is no comparable earlier data on African American MSMs, only the more general figures that include all MSMs.

"These data, combined with recent outbreaks of STDs among MSMs in many cities suggest that HIV incidence may be increasing in this population. And that the epidemic among men who have sex with men in general, and among African American men who have sex with men in particular, is growing worse," she said.

Combing data from several studies, Valleroy concluded that new infections "increase substantially between adolescence and the early 20s. These findings underscore the need to reach each generation of gay and bisexual men early as they enter adolescence, and to sustain these efforts as they grow older."

Count the ways

One underlying principle of statistics is that things tend to even out with larger sets of numbers, while a smaller sample carries greater risk that a few unrepresentative data points can dramatically swing the outcome one way or another. That is exemplified by the "confidence interval (CI)," a range on either side of the statistic where the researcher feels 95 percent certain of the results. The smaller the range of the CI, the greater the accuracy of the statistic, the larger the CI the fuzzier the math. Larger sets of data have smaller CIs and are more accurate.

At first glance the 2,942 young MSMs in the survey is an impressive number. But from that large pool, only 38 were identified as recent infections using STARHS. Because white MSMs constituted the greatest portion of those in Valleroy's research, their incidence rate of 2.5 percent had a CI of 1.4 to 4.6 percent. Hispanics had a 3.5 percent incidence and a CI of 1.4 to 8.6. But because the number of African American MSMs sampled was the smallest of the survey subsets, their incidence of 14.7 percent had a CI of 7.9 to 27.1 percent. That is a huge range.

Valleroy was careful to say in her presentation, "I must underline that the sample size of African Americans is small and that these findings are preliminary. However, we believe these data are of critical public health importance and feel it is urgent to release them now."

The CDC did not release any other numbers, such as how many of those 38 recent infections fell into each of the three racial/ethnic groupings, or how incidence compared between cities. Most - but not all - of the blood samples have been analyzed and tabulated. Valleroy hopes to have all of the data and have it published by the end of the year. In other words, the data that was released was incomplete.

Helene Gayle, who heads up HIV programs at the CDC, said they have "done some statistical corrections" to compensate for the incomplete work, and that affects the confidence intervals.

In an article on the research published by CDC in the June 1 Morbidity and Mortality Weekly Report, the authors were careful to note "at least three limitations" of the study. Among them are questions as to how representative the sample is of MSMs. That is a particularly important issue among young men of color who are less likely to identify as gay or bisexual and thus are more difficult for researchers to identify and recruit into the study.

Valleroy explained how they tried to reach MSMs who do not identify as gay or bisexual, and seemed to sigh when she said, "We obviously couldn't get to the people who were hidden ... we did the best we could."

Gayle added, "The information that we have does not suggest that men who self-identify would necessarily be at greater risk" for HIV. She suggested the opposite, perhaps those who do self-identify as gay or bisexual are more knowledgeable about the risks of HIV and how to protect themselves.

Change and stability

The CDC estimates that 40,000 Americans become infected with HIV each year. It is the same number that they have used since 1992. But if you listen to the various different things that the CDC says, the numbers just don't seem to add up.

Men who have sex with men are still the largest single group (46 percent) of those with AIDS. The CDC says that the rate is explosively high among young black men who have sex with men and less high among Latinos, according to the six-city survey.

CDC does not argue that new infections are falling in gay white men, quite the opposite, citing increases in sexually transmitted diseases, it is worried that new infections are increasing among young gay men. So it does not seem to be a seesaw where increased infections among MSMs of color are balanced by declines in white MSMs.

At the same time we are told that women have the highest rate of increase of AIDS infections of any group. Children have always been a very small portion of total infections, while infection through injection drug use continues at a high level.

With all of these claimed increases going on and little talk of decreases, why has the overall estimate of annual infections remained the same since 1992? When pressed on whether that estimate of 40,000 new infections a year needs to be revised upward, Gayle said, "It's complicated. ... We are looking at developing systems that will give us more precise numbers."

So why did CDC call a news conference to put out incomplete data? It may well be that the "alarm" that Gayle expressed over public health issues was the sole motivation. But one does not have to be a complete cynic to come up with a number of alternative and supplementary explanations.

First, the 20th "anniversary" of HIV was about to occur and CDC did not want to be left out of the flurry of media coverage. It did not have anything else on the shelf, so it rushed the incomplete survey out before it was ready. Gayle is about to depart for the Gates Foundation, so this was her swan song.

And finally, Congress is about to tackle spending bills for next year.

Waiting for publication would take too long for CDC to put forward its best case for more money for HIV prevention activities. Gayle made sure to make the pitch for more bucks at the news conference. "Prevention needs to be expanded, we can't just shift from one population to another."

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