Joan Smith: The woman in the dock can be the victim too

In April last year, detectives arrested a suspect in a Frankfurt nightclub.

The individual was handcuffed, taken away in an unmarked police car and held in custody "because of the danger of repetition" of the alleged offence. She was released after 10 days, despite the supposed risk to the public, and last week she went on trial in Darmstadt. The woman in question is a singer whose band represented Germany in the 2008 Eurovision song contest, and the sensational accusations against her – having unprotected sex several years ago without telling her lovers that she was HIV-positive – have made headlines across the world.

Nadja Benaissa is a beautiful young woman and a member of No Angels, the German equivalent of Girls Aloud, so the case was always going to get a lot of publicity. But Aids activists say that at least 600 people in 40 countries have been convicted of offences in relation to HIV, even though most cases haven't involved deliberate intention or transmission. The spectre of "Aids avengers" infecting unsuspecting sexual partners was raised repeatedly in the early days of the virus but there's little evidence that such people exist, while the persistence of the myth is a reflection of the stigma that still attaches to being HIV-positive.

Ms Benaissa is accused of having unprotected sex around five times between 2000 and 2004 with three different men, one of whom discovered in 2007 that he was HIV-positive; she has been charged with grievous bodily harm in his case and attempted aggravated assault on the other two men. In court, she apologised for putting the men at risk, admitted being careless and said that she had never intended to pass on the virus. "I'd been told the likelihood of infecting someone or that I would develop the illness [Aids] was more or less zero," she said in a statement.

The trial raises troubling questions about whether a court is the proper place to deal with issues around illness, infection and sexual behaviour. The fanfare with which Ms Benaissa was arrested last year amounted to a public humiliation – Aids activists have described her treatment as a "witch hunt" – while the fact that the alleged offences were at least five years old suggests there was little need to hold her in custody. A key factor in her defence will be the possibility that her ex-lover could have been infected by someone else, but in any case the 34-year-old man agreed to unprotected sex on around three occasions. "You have unleashed a lot of misery into the world," he told Ms Benaissa in a courtroom confrontation, apparently ignoring the fact that adults have a responsibility to look after their own sexual health.

Another way of looking at this case is that it highlights the lack of support in Germany for young woman from immigrant families; Ms Benaissa's father is Moroccan, her mother Serbian-German. She began using crack cocaine when she was 14, became pregnant at 17 and discovered her HIV-positive status after a routine test during her pregnancy. That's a great deal for a teenager to cope with, no matter how resilient, and it's not entirely surprising that she kept her status secret even from close friends. A year later she went on a reality TV show, won a place in No Angels, and pop stardom appeared to offer a second chance in life. Now, if convicted, she faces a jail sentence.

If this is a morality tale in any sense, it's surely about the need to support teenage girls so they don't start having unprotected sex at such a young age – and the urgent need for high-quality Aids education.

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