It is 10 o'clock on a Friday night in Soweto, Johannesburg's most famous township, but it's still early for The Rock, a nightclub popular with the young and upwardly mobile, and most potential patrons are drinking at a shebeen [informal bar] operating in the parking lot.

Mapule, 24, a part-time student from Boksburg, a town on Johannesburg's eastern outskirts, and her friends [last names withheld] have staked out a table inside. "We come here to mingle; we see all our friends here," she says.

Mingling includes meeting men. According to the girls, The Rock attracts "all sorts", but Mapule and her friends prefer them in their late twenties, with enough disposable income to keep the good times coming.

"I wouldn't date a guy my age because he wouldn't be able to afford my level," says Mapule's friend, Shoni, 25, a brand consultant from Pretoria. "Why would you want to date a guy who can't even afford to buy himself a beer?"

The girls are all in relationships with boys their own age, so flirting with men who are five or 10 years older is "just for fun" and not the same as having a "sugar daddy" who, according to Mapule's definition, is "old and has lots of money and is going through a midlife crisis".

In fact, having a partner even five years older can significantly increase HIV risk. A 2005 survey of HIV prevalence among people aged 15 to 19 by South Africa's Human Sciences Research Council found that women with partners at least five years older were four times more likely to be HIV positive than women with partners nearer their own age.

"Black Diamonds" - the new sugar daddies?

While sugar daddies are not a new phenomenon, their latest incarnation could be described as a symptom of the "new" post-1994 South Africa with its rampant consumerism and glittering shopping malls, located just a few kilometres from informal settlements where people still live in shacks.

Nowhere are these jarring inequalities more apparent than Johannesburg, South Africa's economic hub and the natural territory of "Black Diamonds", a term coined to describe members of the new black middle classes.

Most of this group have long abandoned the townships for Johannesburg's upmarket northern suburbs, but many still return on weekends to drink in shebeens and flirt with young women, who are easily impressed by their flashy cars and designer clothes.

Mapule's description of a sugar daddy matches the stereotype of a middle-aged man using his wealth and status to lure young, vulnerable women, which has been cited as one of the drivers of sub-Saharan Africa's HIV epidemic.

But in the South African context at least, this definition of a "sugar daddy" is something of a misnomer, according to Dr Mickey Chopra, head of the Health Systems Research Unit at South Africa's Medical Research Council (MRC).

Profile of a sugar daddy

At the end of 2006, Chopra led a study in Cape Town, in Western Cape Province, that looked at the sexual risk behaviour of 420 men aged 25 and over, and who had had sex with more than one woman at least five years younger in the previous three months.

The age difference between the men and their partners was less critical than the economic disparity and the "power differential" it created, he told IRIN/PlusNews. "They said all the times they had sex, there was some sort of transaction that happened."

The average age of the men was only 28, but they tended to be better educated and have more disposable income than was typical for the area. More than half reported inconsistent condom use with an average of six sexual partners in the previous three months; less than half considered themselves at high risk of HIV infection, but of those who agreed to be tested, 12.3 percent were positive - twice the average for the area.

In focus group interviews, the men described a set pattern of behaviour. "From Monday to Friday they'd have their regular girlfriends, then on Friday afternoons they'd meet with their mates, maybe have a braai [barbeque], then go to the shebeens to meet women, and that would continue until Sunday afternoon," Chopra said.

"The expectation in their social group is to have concurrent partners; there's a sense that the more girlfriends you have, the higher your standing in your social group."

Victims or willing accomplices?

The MRC is now recruiting for a study that will look at women's motivations and risk behaviours in their interactions with sugar daddies, but Chopra's impression is that "these are women who know what they're doing - it's to try and have some fun and get those extra things."

Mapule and her friends confirm that women are rarely passive victims in these relationships. "For us, they're someone you can use for drinks and going out and everything's paid for, but we never get intimate with them," Mapule insisted.

She and her friends all have stories about older admirers whom they milked for drinks and gifts. "There was this one who really liked me," recalled Nunu, 20, from Soweto. "He bought me lingerie and perfume."

"I knew one," added Mapule. "He owned a bar. He would send a car to come and fetch us and we'd get free drinks all night, but then he wouldn't want me to leave."

"They feel like they own you after a while," said Nunu. "They start telling you, 'I don't want you to party unless you're with me.'"

Mapule and Nunu said at this point they broke things off, but not all their acquaintances were willing to give up the perks of dating older, wealthier men. "When it starts, it's all about the money, but they [the women] get hooked on that," said Mapule.

A two-way street of "extras"

Just a few blocks from Nelson Mandela's former, modest home in an area of Soweto called Orlando is Nambitha's, a popular spot for traditional African food at non-traditional prices and one of a number of establishments in the township catering to the Black Diamond crowd.

"We come to Soweto to eat good food and see good people," says Moses, 32, [not his real name], a shipping industry executive from the east-cost city of Durban. "It's a lot more relaxed here in terms of culture; I mean, when we shout, no one's going to tell us to keep our voices down."

Moses is well-acquainted with The Rock, which he describes as a notorious pick-up joint. "There are too many beautiful girls there: it's too tempting," says his colleague, Xolani [not his real name], a married 38-year-old who lives in one of the city's northern suburbs.

The men also talk knowledgeably about the advantages of dating younger women. "An older woman, she wants commitment; all younger women want is money. The younger ones, they are the more beautiful and as long as there's money for [cellphone] airtime and for their rent," says Moses.

"There are so many attractions in the city: they want the nice shoes from Sandton City [an upmarket shopping mall] and the Gucci watch. You come around in your Range Rover, wearing all these big labels, and they think maybe there's a bit of cash here," adds Xolani. "Often, they have a regular boyfriend who's their age, but over and above that they want a sugar daddy for the extras."

Such relationships have perks for both parties. "From [the men's] side, they like the fact she's not all over him all the time, and chances are a younger woman is going to be more submissive to an older man," he says.

Moses and Xolani refute the MRC study findings that men sleep with multiple younger women to assert their wealth and social status. "If someone tells me he has 10 girlfriends, I'll be thinking, 'who is this fool?'. Having many partners is a sign you're still immature," says Moses.

"I think people are waking up to the fact there's HIV and you have to protect yourself," nods Xolani. "Married people, if they don't use a condom [with casual partners] this person could be HIV."

Targeting the men

Moses and Xolani scoop up their cell phones and the keys to their expensive cars. They're headed for The Backroom, Soweto's swankiest bar, where bouncers enforce a "no sneakers" policy and the crowd is more mature than at The Rock.

Here, men who have squeezed their middle-aged spread into white trousers and pastel coloured shirts are trailed by younger women in tight jeans and high heels, while DJs blast thumping dance tracks and televisions are tuned to a fashion channel featuring endless scantily clad models.

Chopra worries that too few HIV/AIDS awareness messages target older men. Instead, most have been aimed at young women, who may not be in a position to reduce their HIV risk if their boyfriend is part of a large sexual network they are not even aware of.

In a follow-up exercise to its 2006 study the MRC will identify 30 "opinion leaders" who fit the sugar-daddy profile and are willing to participate in a series of training workshops. They will then be dispatched to shebeens and taverns to spread the word to their peers.

The workshops will focus on the issues of concurrent partners and condom use. "Those are the two behaviours that are very important epidemiologically, and the ones we can hopefully change," said Chopra. "Changing the age difference and transactional thing is more difficult."