WHEN Marie found she had pneumonia last January, she thought: 'Oh Jesus, this is the start of it.' For her, it was the inevitable beginning of the nightmare that she had dreaded for five years. Marie knew she was HIV-positive, and that a bout of pneumonia did not simply mean a week in hospital but the start of Aids. 'I knew it was my sickness coming on,' she says. 'I will be in and out of hospital from now on, but I have the will to live, not only for myself but also for my children.'

Marie, a slight, dark-haired mother of two, looks fit and well despite her struggle against Aids. She first discovered she was HIV-positive in 1987, when she went into a residential drug treatment centre. 'I blocked the news out of my mind and lived my life as though it never existed, but this year I have been ill three times, so I have had to face up to it.'

Marie, who is 29, is one of 2,500 women in Britain who know that they are infected with HIV and one of 700 who contracted it from injecting drugs. She got into drugs when she came to London from the west of Ireland when she was 17. 'It was just a weekend thing. I was not a junkie and I wasn't sleeping around, which is why I was so shocked when I found I was HIV-positive.' Her daughter, aged 10, was born before she became infected and her son, 3, who was born after she contracted the virus, managed to escape infection. Like many women with Aids, Marie's children are among her greatest worries. 'I am going to fight this until both the children are old enough to fend for themselves,' she says.

She is suffering from an epidemic that now affects 10 million people across the globe. Their plight is being highlighted today, World Aids Day. She was fortunate in some ways in knowing she was HIV-positive before symptoms started. When she called her GP after five days lying ill in bed, she was able to tell him that she was HIV- positive, and he immediately knew that she had an Aids-related infection. He rushed her into hospital. She was back at home 10 days later.

Others are not so lucky. Although doctors are often quick to spot HIV symptoms in men, especially in those whom they know to be gay, there is strong evidence that they miss the first signs in women because they do not perceive Aids to be a female disease. Some women have died during their first bout of Aids-related pneumonia because no one thinks of the diagnosis until it is too late.

'I have seen two women in the last 18 months who have come into hospital and who have died within two weeks from end-stage HIV infection,' says Dr Margaret Johnson, consultant in HIV/

Aids at the Royal Free Hospital, London. 'In both cases they had been seen by GPs or casualty staff and been diagnosed as having asthma or a chest infection. With women, HIV is something that a GP or casualty officer often does not even think to ask about.'

Her words are echoed by Dr Danielle Mercey, consultant in genito-urinary medicine at the Middlesex Hospital, London. 'I have looked after two women patients whose diagnosis has been seriously delayed by doctors not spotting symptoms, which were classic for pneumocystis pneumonia (Aids-related pneumonia) and no one thought of it,' she says. One patient has subsequently died and the other is seriously ill.

Dr Johnson and Dr Mercey want to see the 'normalisation' of HIV and Aids, so that it is discussed more frequently with patients, whether they are attending a GP's surgery, a family planning session or an antenatal clinic.

Dr Johnson says: 'I don't find it hard to ask patients, do you sleep with men or women? Do you use drugs? But some doctors get embarrassed and believe the only people who should ask these questions are trained Aids counsellors.'

She fears that if hospitals and GPs wait until there is an army of HIV/Aids counsellors before the issue is tackled, the disease will continue its insidious spread without hindrance.

'We had a three-month-old baby admitted to our hospital recently who died of pneumocystis pneumonia. Neither the baby's mother nor the doctors knew that the mother was HIV-positive so HIV did not cross anyone's mind. That is the worst possible way for a family to find out,' Dr Johnson says.

To prevent such devastating occurrences, Dr Johnson and many other doctors, including obstetricians as well as Aids specialists, believe HIV testing should be offered routinely at antenatal clinics. The British Medical Association backed such a move 18 months ago, but only a handful of hospitals provide this service. Dr Johnson's own hospital offers it only to those women whom they perceive to be at risk.

The problem with simply guessing which patients are at risk is illustrated by the fact that Marie, a former drug user who was HIV-positive during her second pregnancy, was never tested and not known by doctors to be infected. Other hospitals are considering introducing testing, but the wheels of the NHS grind exceedingly slow. The Department of Health has spent more than a year drawing up guidelines that will not be issued until next year.

Mr Stuart Steele, consultant obstetrician, who is chairing a committee on routine testing at University College Hospital, London, feels strongly that it should be introduced. 'Many of our patients think they are being tested when they are not. We have had women whose babies have become ill with HIV infection, who are shocked and angry to discover that they were never tested during pregnancy.'

Doctors have been carrying out anonymous HIV tests on all pregnant women at UCH for several years. Their results show that for every woman who knows she is HIV-positive, there are four others who do not know they are infected.

'At the moment we have to pick out those people whom we think might be at risk to offer them testings and that can appear discriminatory if we approach someone who is African, for example,' says Mr Steele.

He feels it is vital for women to know their HIV status so they can decide if they want to get pregnant in the first place; or continue with a pregnancy; or be advised about breast- feeding. Early treatment for both woman and child can extend healthy life dramatically.

Dr Judy Bury, a primary care facilitator in the HIV/Aids and drugs team for Lothian Health Board, says: 'Of course antenatal clinics should offer the test to all women. The more they play this game of thinking they know the women at risk, the more they miss those who are infected.'

Dr Bury, who is co-author of a new book, Working with Women and Aids, to be published by Routledge on Thursday, believes it is essential that more research is carried out into how the disease progresses in women, since most large studies have concentrated on men.

Doctors in the United States have been worried for some time that women who become infected with HIV appear not to survive for as long as men in the same situation. Now two large-scale studies are being set up on either side of the Atlantic to address the issue.

Doctors at the Middlesex Hospital are co-ordinating a UK study that will chart the progress of 500-600 women over three years initially, and probably longer. Funded by the Medical Research Council, it is going to cost pounds 300,000 and will cover nine centres, eight in London and one in Edinburgh. The equivalent US study is going to be larger and will cost dollars 4.5m.

One of the points to be researched is whether cervical cancer is more common in HIV-infected women. Researchers have discovered a higher rate of abnormal cervical smears among women with the infection but do not know whether higher rates of invasive cancer result.

In the US, the Centers for Disease Control in Atlanta, Georgia, is planning to change the definition of Aids from January to include cancer of the cervix as one of the Aids-indicator diseases, and it is likely that Europe will follow suit.

The new study is welcomed by Hope Massiah, development manager of Positively Women, a self-help organisation for women. She says: 'This is long overdue. Most of the information that people have been working with is based on research done on men. There is a lot of anecdotal evidence that HIV affects women differently.'

With more research and more action, doctors and campaigners hope to smash the invisibility of women with Aids.

Positively Women Helpline: 071-490 2327, between 12 noon and 2pm, Monday to Friday.