An autopsy revealed no obvious injuries but put the death a full week before she was found. No cause of death has been announced, although several types of prescription medication were found in the apartment.

A staple for the tabloid media during her lifetime, the willowy Iijima was just as popular in the days immediately after her death. Reports speculated about whether she had died as a result of illness, suicide or a criminal event.

'Her room was messy, with books, clothes and bottles strewn around where she was found,' a police investigator was quoted as telling the weekly Shukan Post magazine. 'We found several packs of different brands of cigarettes. It seems that she was with someone up until the last minutes of her life.'

Despite hints at foul play or a cover-up by the authorities, it could be considered odd that the autopsy failed to determine the cause of Iijima's death - until one considers that in Japan, revealing that one is ill is considered shameful and that even people being treated for cancer or other serious ailments are not told precisely what is wrong with them by their physicians.

Stars of stage, screen and the pop world are equally unwilling to involve themselves in causes that could associate them with an issue or incite a whispering campaign - such as HIV/Aids awareness.

Iijima, however, was one of the very, very few recognisable faces who did speak out on this issue, right up until her death.

Her involvement in spreading the word about HIV/Aids began around 2000, coinciding with the release of her book Platonic Sex. The book - which has sold more than 2 million copies and was turned into a television drama and a hit, big-screen movie - described her life as a porn star and bar hostess.

It pulled no punches. It detailed how Iijima, born Matsue Okubo in Tokyo, was raped in her early teens, had an abortion and ran away from home.

'I hated my parents,' she wrote. 'It reached the point where I would rather learn from tramps and sleep in parks wrapped in newspapers for blankets.'

To survive, she worked as a hostess and helped make enjo kosai, literally 'compensated dating' but effectively prostitution, an almost fashionable pastime for thousands of young Japanese women. She drifted into the blue movie business and quickly rose to be one of its best-known and best-paid stars, appearing in more than 100 titles.

A short-lived music career was followed by bigger success on daytime talk shows, where producers and audiences enjoyed her refreshingly frank delivery and discussion of the issue of the day. One topic that was apparently dear to her heart was Aids in Japan, and with good reason.

'The infection rate is increasing in Japan, unlike in other developed nations, and we have never seen that figure go down,' said Shiggy, a counsellor with the Japan HIV Centre who would give only one name.

'It is a Japanese trait to think 'my boyfriend can't possibly have Aids' or 'my girlfriend won't be HIV positive', but young Japanese people don't take precautions.'

According to the organisation, around 15,000 Japanese have tested positive for HIV - but as many as four times that number have not been tested and are unaware they have the disease.

'People say it is nothing to do with them, that they don't need protection,' Shiggy said. 'Even in the sex industry, some places do not require that customers wear a condom. There is also lots of peer pressure in companies, with senior employees taking new staff out for drinking sessions that end up with them being forced to go into commercial sex establishments.'

Iijima kept up a popular blog, even after her retirement from the media world in late 2006 at the age of 34. She used the blog to announce that she was suffering from health problems, prompting the initial rumours that she was about to retire. Various tabloids reported that she was suffering from a mild form of neurosis, hay fever, infections of the urinary tract, cystitis and kidney problems. Some of the reports were confirmed in her blog, which kept coming back to the topic of Aids.

In a post dated December 2, 2007, she wrote: 'Today, someone is dying from Aids. Every day, the number of people infected is increasing. For myself, and people that I care about, I would take an HIV test.

'My first test took a lot of courage and it was very frightening until the result came back. I can still remember being worried,' she wrote. 'But every year since then, I have taken the same test. For the people who are important in your life, you should take the test.'

The last entry on the blog was dated December 5, and the following day she spoke at an Aids seminar. One of her planned new business ventures was selling condoms to women, although there are also reports that she had fallen out with her financial backers and was experiencing money problems.

Iijima had no shortage of critics, who saw her commitment to the Aids cause as more designed to promote herself and make a living.

'Generally speaking, people did not take her seriously when she talked about Aids because she was just using it to sell herself,' says Toshiko Marks, a professor of multicultural understanding at Shumei University. 'She had little talent as an actress or singer, and as she got older she needed something to define her own life.

'She needed a venture to be profitable and, as she knew a lot about HIV and Aids, she used that to sell herself. No one will ever be able to say that she had the disease; she never stated it clearly, and that gave her authority.'

But might Iijima have been the catalyst for Japanese society at last openly discussing what much of the rest of the world has recognised as a major threat?

'Sex is everywhere, but nobody wants to talk about it,' Professor Marks says. 'But in the next few years, it is possible that we might start talking about these issues.

'Young Japanese people are not keen on the shape of our society today and the way in which it hides issues like this. They see that approach has not worked in the past, and think that if they talk about something then they might be able to change it. Confronting a problem is better than ignoring it. That does not make it go away.'

She may very well have a point.

The Japan HIV Centre received 124 calls from worried people on January 5, the first day its hotline was open after the New Year holiday and days of headlines about Iijima's death. That figure was a record, according to Shiggy.

Iijima's legacy might be hundreds of Japanese surviving a disease that has already killed millions around the world.