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Long-term Tokyo resident and HIV sufferer Neil Grainger says he still doesn't have any idea how he was infected with the deadly virus.
"With the information presented to me by my doctor, I believe I contracted HIV during my early 40s, a time when I wasn't particularly promiscuous or taking risks," he says.
"It is a bit of a mystery whom I contracted HIV from, as the few people I contacted after being diagnosed - those who potentially could have transmitted it to me - all claim to be negative and therefore, if they are telling the truth, I couldn't have contracted it from them."
Grainger, a gay, 44-year-old Englishman, acknowledges there is one former boyfriend whom he has been unable to contact since he knew about his status, but he says there were no signs at the time he had HIV.
He says he was very aware of the risks of contracting HIV and as a rule practised safe sex, but after forming a close relationship with someone he gradually let down his guard.
Grainger believes the most likely explanation for how he contracted the virus is that the person who infected him was unaware of their own status.
Grainger himself discovered he had HIV completely by accident.
In July last year he was diagnosed with Stage 3 malignant melanoma and had to undergo surgery immediately to remove the tumour. During the course of carrying out pre-surgery screening tests, the doctors discovered he also had HIV.
"It is fair to say that if I hadn't been diagnosed with cancer, I may well be unaware of my HIV status to this day. There is a definite lack of testing going on in Japan," he says.
He says he knows of one clinic in Shinjuku Ward in Tokyo (Japan's famous gay district Ni-Chome is located in Shinjuku) that routinely offers free HIV tests, but in comparison to his home country there are less opportunities and encouragement to get tested.
"In the UK free HIV tests can be carried out at thousands of locations and this is promoted through advertisements and posters almost everywhere.
"There is a definite lack of a push to get tested here," he says.
That said, Grainger believes fear of a positive diagnosis is the main reason why at-risk people don't get tested.
"The 'ignorance is bliss' attitude to HIV status is still prevalent, mainly because people still think of the virus as it was portrayed years ago. If people were aware of the medicines available and aware that HIV is no longer a terminal disease, they may be more willing to be tested as the fear of being diagnosed positive may not be the reason they avoid the test," he says.
According to Japan's Ministry of Health, Labour and Welfare's Aids Surveillance Committee, there were roughly 1500 newly reported HIV patients in the country last year.
The total number of patients nationwide on an accumulated basis is now more than 21,000 - 14,706 of whom are HIV-infected and 6719 have Aids.
The Ministry of Health's figures exclude people who historically contracted HIV via botched blood transfusions.
During the 1980s there was a major HIV-tainted blood scandal in Japan and it is estimated that about 1400 hemophiliacs - about 40 per cent of patients treated between 1982 and 1985 - contracted HIV via non-heat-treated blood products.
The scandal resulted in a high- profile, class action lawsuit which the Government lost in 1996 and was the key event that first brought HIV/Aids to the awareness of the Japanese public.
Of the new HIV/Aids cases reported last year, 94.7 per cent were men and 5.3 per cent were women. Regarding HIV cases only, 72.3 per cent contracted HIV through homosexual contact, 18 per cent through heterosexual contact and 0.5 per cent through IV drug use.
In 7.5 per cent of the reported cases the cause of transmission was unknown and 1.8 per cent listed as "other causes", according to data released by Japan's Ministry of Health.
There were no cases of HIV being passed from mother to daughter during pregnancy recorded in 2012 in Japan.
Grainger says he is also concerned about the lax attitude to safe sex, even in high-risk situations.
"There is a lot of unsafe sex practised in Japan in places where you would expect safe sex to be standard in the West, such as saunas or cruising areas.
"Also, these places are popular with openly gay men and closeted gay or bisexual men, meaning that a good percentage of people who frequent this kind of establishment are also in a relationship with a woman or even married," he says.
Grainger says that although he no longer frequents Tokyo's gay cruising spots, he did in his earlier years and he says he was surprised by the lack of encouragement to practise safe sex.
"It is shocking, for example, that Ni-Chome's most famous gay hattenba (sauna), '24 Kaikan', doesn't provide easy access to free condoms. If you want a condom, you need to either take one with you or ask at the front desk.
"As a lot of people also use this kind of place as a form of cheap accommodation after drinking in the area, [they] may be more prepared to take a risk than they would do normally.
"On the occasions that I have stayed overnight at 24 Kaikan, the amount of men who seemed completely disinterested in using a condom was quite shocking."