Thursday, August 30, 2012

HIV Rorschach Test: It's All About Sex, Say Researchers

Several commentators who were working in African health facilities in the 1980s, when HIV started to be diagnosed, have said that their earliest clients tended to be male, employed, mobile, relatively well off and relatively well educated. While it may at first have been suspected that these were the very people who were most likely to have access to health facilities, which may have made it appear that the above characteristics were significant factors in HIV transmission, population based surveys carried out later confirmed that there often was a marked correlation between HIV status with education and wealth, among women as well as among men.

Concentrating on education for the moment, Hargreaves, Slaymaker, Fearon and Howe have this to say: "HIV prevalence trends in Tanzania differ between socioeconomic groups. While HIV prevalence was initially higher among those with higher levels of educational attainment, it has fallen fastest among these groups. Among those with lower levels of education HIV prevalence has been stable. The behavioural dynamics underlying this phenomenon remain unclear...".

While the data doesn't say that more education means less HIV, it may say something about education. Perhaps the researchers are hinting that those who had access to education were able to modify their sexual behavior, at least to some extent, in response to safe sex campaigns; HIV prevalence declined in some population sectors. Whereas, those who had less access to education, or none at all, didn't modify their sexual behavior, or did so more slowly; and HIV prevalence stagnated. But the authors list many limitations to their study and recommend further research.

To demonstrate how this hinted at mechanism may work, the researchers go on to suggest a theory that might contribute to providing "a framework to aid interpretation of emerging data". This theory is called the 'inverse equity hypothesis', which "suggests that the introduction of health interventions will tend to benefit those of the highest socioeconomic position first, only later benefiting those in lower socioeconomic groups", except that the health interventions in this instance were health education interventions, specifically.

Then comes the breathtaking sleight of hand, the fallacious move from HIV prevalence rates to rates of 'unsafe' sexual behavior: "Although little data on sexual behaviour are available from earlier in the epidemic, in the 1980s to 1990s prevailing sexual risk patterns must have been higher in higher socioeconomic groups because these groups had the highest levels of HIV prevalence in early studies." The fallacy has a long history; it's called 'affirming the consequent'. If A then B; B, therefore A (where A is 'high sexual risk' and B is 'high HIV prevalence').

Don't get me wrong; some proportion of HIV is accounted for by sexual behavior. But what proportion, and what kind of sexual behavior, exactly? And some proportion of HIV must be accounted for by certain non-sexual modes of transmission, probably involving unsafe healthcare, cosmetic and traditional practices. In the syllogism above, we must be able to explain B without begging the question about A; A must be shown to have caused B, not assumed to have done so without evidence.

So let me finish by saying why I also think the inverse equity hypothesis may have a role to play in accounting for the HIV epidemic in Tanzania and in other African countries. Men who are employed, mobile, well educated and relatively well off, what the authors refer to as "those of the highest socioeconomic position", may benefit from health interventions, that's true. But if health facilities are unsafe places, where common skin-piercing procedures such as injections may carry a high risk of transmitting HIV, hepatitis, bacterial infections and the like, men may also be among the first to be infected with whatever is going around in the blood-borne infection department.

Think of it this way, for example: factors such as mobility and wealth may facilitate unsafe sexual behavior. But unsafe sexual behavior can result in sexually transmitted infections (STI). Wealthier and better educated people with jobs are far more likely to have access to health facilities, not just at home, but away from home, where STI clinics would be more anonymous.

If Tanzanian businessmen travelled to Uganda or the Democratic Republic of Congo in the early 80s, where HIV prevalence was already higher than at home, a visit to a sex worker would have involved the risk of infection with HIV or some STI or other. But a visit to an STI clinic would almost certainly have included the risk of transmission of some blood-borne infection; especially before HIV was even recognized, but even after, when health facility transmission may not yet have been idenfitied. Why not investigate non-sexual transmission, and even look for data, rather than plugging an empirical gap with a logical fallacy?

[For more about non-sexual HIV transmission and mass male circumcision, see the Don't Get Stuck With HIV site.]


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