Editor in Chief of Positive Nation, the UK's HIV and sexual health magazine
How did HIV come to afflict Africa so much more than other parts of the world?
Africa does have an injection culture
Is the ferocious spread of the virus at least partly due to the use of unsafe medical practice, such as using unsterilised needles for injections rather than sex?
That is certainly the controversy between experts.
In his article in the International Journal of Sexually Transmitted Diseases (STDs) and Aids, Dr David Gisselquist has questioned the importance of dirty needles in spreading the disease.
Speaking to me in London, he said: "When you're looking at HIV doubling in a year, as it has done in some African countries, you have a hard thing to explain if you think it's due to vaginal sex.
"There is additionally a problem in countries like Zimbabwe where STD rates were actually falling as the HIV rate was climbing.
I think these guys are completely unaware of what their impact might be in Africa
Catherine Hankins, the chief medical officer at UNAIDS
"And it can't be simply due to a 'time lag' effect - people caught the STDs last week, but they caught HIV two years before testing - because the attrition rate in Africa due to Aids is so high you need ongoing transmissions in order to sustain high prevalence.
"The few African studies that have been done show heterosexual infection rates between couples no higher than in the West. And when we looked more closely at those studies and measured the risk factors for people who became positive within a specific year, it was only 15% more risky to have had multiple sexual partners rather than just one.
"When you ask the same question about having injections, the additional risk averaged at 28%. So having an injection is twice as risky as having several partners."
But others believe Gisselquist's paper is flawed.
Catherine Hankins, the chief medical officer at UNAIDS, is clearly angry about the papers by Gisselquist and others, and the reaction they have generated.
"We all agree medical safety should be on the agenda.
"In fact I was instrumental in including the cost of providing safe injections in the UNAIDS estimate of the cost of global Aids prevention."
But she said the data they had compiled could have an adverse affect on health in Africa.
"I think these guys are completely unaware of what their impact might be in Africa.
"A woman is trying her best to get her man to use condoms and to get immunisations and medical care for her child. How's she going to react if she's told condoms may not be necessary, but is scared off taking her kid to the doctor? It's not a question of we either provide clean needles or condoms."
In any case, she says, Gisselquist's arguments don't stand up.
"We estimate that 25% of injections in Africa are unsafe. But in Asia 50% are unsafe. There's a much bigger culture of getting vitamin shots from a stall in the marketplace there. Why didn't Asia get the big epidemic first?"
The difference between the two continents, Hankin says, may lie "in the fact that Asia has way lower STD rates than Africa."
She cites recent studies that show it's not the 'classic' STDs that make people much more infectious, and infectable, with HIV. It's the 'hidden', asymptomatic ones- HPV (genital wart) virus and, in particular, asymptomatic herpes.
The other thing you'd expect if most of HIV in Africa were caused by needles is lots of hepatitis C to go with it. Hankin insists: "Everywhere where drug users have high rates of HIV, they have even higher rates of hepatitis C. But in South Africa the rates are 20% and 0.1%, respectively.
"There's also the evidence from medical needlestick accidents. In cases where medical personnel accidentally spiked themselves with HIV-contaminated needles, the infection rate was 0.33% - one in 300."
As Hankin surmises, in some cultures what you do with your sexual partners over time is different. In the West we tend to be serially monogamous.
In Africa, if you've had sex with someone at some point, the door isn't considered closed on picking up on that relationship again.
"Take a middle-class African businessman. He has had five women - nothing excessive. But the pattern we find is that he has a wife. He also has an on-off affair with an office colleague. He also has what the French call a 'deuxième bureau' - a mistress who might have a child. And once a year he goes back to his home village and has sex with his original village sweetheart. Then he gets HIV from a bar girl on a business trip.
"Within a year he may have infected four other women. Now, if I've had five sexual partners and catch HIV from the fifth, as a western woman I'm unlikely to return to the other four and infect them!"