London, UK - Almost 30 years since HIV was first identified, the virus still carries a stigma that can prove deadly.
In the mid 1980s, uncompromising government television advertisements told people, "don't die of ignorance".
But, 21 years after the first World Aids Day in 1988, people are still dying of ignorance.
A large proportion of infected people are unaware that they carry the virus, and, such is the taboo surrounding HIV, many of them would rather stay in the dark.
Of those who do know that they are infected, they are desperate not to admit it.
Religions are often credited as the means by which moral values, such as care for others, are reinforced and passed on.
But some charities and anti-HIV groups claim religion is helping to breed the very stigma that the UN says has helped give the UK twice as many new cases of infection each year as any other country in western Europe.
The UK's Health Protection Agency says the number of estimated cases rose by 8% between 2007 and 2008.
But it is thought 22,000 of the 83,000 people with HIV do not know they are infected.
Barrier of ignorance
In denouncing the behaviour that allows the virus to spread, religious leaders sometimes drive HIV-positive people underground.
The same black and white approach can also prevent faith groups from promoting practical measures - such as the use of condoms - because they may be seen as condoning "immoral" behaviour.
Veena O'Sullivan, who heads the HIV Unit in the Christian development agency Tearfund, says stigma and ignorance remain among the greatest barriers to tackling the Aids pandemic.
"The church at its best can be a source of great hope and support to people living with or affected by HIV, but ignorance and prejudice remain within the church."
Another charity working to prevent Aids, the African HIV Policy Network, is recruiting religious leaders in the fight against HIV stigma.
It has devised what it calls "tool kits" of advice and information designed to make mentioning the unmentionable easier for clergy and other faith leaders.
It has appealed to them for help because they have influence with a particularly vulnerable group - black Africans.
According to Dr Shima Tariq, who has studied the transmission of HIV, more than half of newly diagnosed patients caught HIV through heterosexual sex, and two-thirds of them are of black African origin or descent.
But most of this group are not Christian: six out of 10 are Muslim.
Ibrahim - who's a Muslim and came to Britain from Ivory Coast - is HIV positive.
"It's quite difficult for me because the thing is I can't tell anybody. Because my family...nobody knows. None of my friends know. Nobody.
"Because if I tell them they will leave me alone and I will have to live alone and it will be a hard life for me."
Along with a conservative African culture, religion has played a significant role in creating this taboo. Ismael is 40 and originally from Sudan.
"The imams don't talk too much about it, but they start off by saying 'this is a taboo, this is a sin, a punishment from Allah'.
"When you disclose it, straight away they think you are gay, or maybe you got it from a prostitute or you did something bad and Allah is punishing you. That is why it has to be kept secret."
So the African HIV Policy Network has asked imams to break the taboo by talking openly about HIV.
One of them, Mohamed Bashir of the North Brixton mosque in London, says imams need to acknowledge "that not everyone practices their religion to the letter".
"There are Muslims who go to the mosque, who pray. They do everything similarly nicely and they suffer moments of lapse in judgement.
"They have extra-marital relations that they will not speak about, and engage in risky behaviour. Some imams might not want to admit that."
Mohamed Bashir has agreed to train other imams on how to tackle the taboo.
He accepts that in the face of HIV, condoms may be the lesser of two evils, but says communicating that to a congregation is a sensitive issue.
"It won't be considered responsible for an imam to say 'when you're making a mistake make sure you use a condom', because that could be misunderstood as condoning that particular activity.
"In our awareness programme, literature is presented to members of the Muslim community. They can go to GM clinics, they can anonymously stock up on condoms.
"But to actively share them out, that wouldn't be proper for an Islamic centre or an imam probably to do that."
Imam Bashir reminds his congregation that Islam teaches its followers not to judge each other, and is bringing HIV out of the shadows.
He says there's not a moment to lose.