In Botswana and other nations in southern Africa, AIDS experts say high rates of sexual networking with multiple, concurrent, and enduring partners are partly to blame for driving the epidemic's spread.
A second issue is the low rate of circumcision, a procedure that removes the foreskin and its easily infected cells. "There's no place in the world where you have very high HIV and you don't have those two factors," said Daniel Halperin, a former US AIDS prevention advisor in Africa.
Persons newly infected with HIV experience a huge surge in viral load and can easily infect sex partners before the infection can be identified by standard tests. During this time, networks of concurrent, multiple sexual relationships can be saturated quickly with HIV. This is especially true for enduring partners, who tend to rely on condoms less.
That viral spike means a world of difference between having multiple sex partners over one year and the same number over one month. In a model presented at Princeton in May, a small increase in the average number of concurrent sexual partners -- from 1.68 to 1.86 -- had major effects, spreading HIV through the tangled network so fast it resembled a major city's transport lines.
In Botswana, a 2003 survey sponsored by the US government found that about one in three sexually active men reported having multiple, concurrent sex partners, and 14 percent of women reported the same. Among men younger than age 25, 44 percent reported multiple, concurrent sex partners.
Rent, clothing, and even cell phone airtime can be parlayed into sexual exchanges, said Faruk Maunge, a high school counselor who has lost many acquaintances to AIDS. In 2004, 25 percent of adults had HIV/AIDS in the country, second to Swaziland. With so many adults ages 35-50 dead from AIDS, the younger generation "are just a lost bunch," Maunge said. "They are very, very reckless."