The biggest city in India, Mumbai, is estimated to have more than 30 red-light areas. But the most famous is Kamatipura, a warren of more than a dozen narrow streets between two railway stations. Dressed in garish saris, the women, who range from young teenagers to the middle-aged, compete for attention with the sweet sellers and shoe-shine boys.
The area has attracted the attention of health workers ever since the mid-1990s, when it has been estimated that around half of the prostitutes in Kamatipura were HIV-positive. Their fate is taking on a new urgency because of the fear that the disease is rapidly spreading out in to the general population.
There are two very different views about the Aids situation in India. On one hand, the government says that the risks presented by Aids are heavily exaggerated. The National Aids Control Organisation, known as Naco, which co-ordinates the country's response to the spread of the disease, has routinely stressed that India remains a low prevalence country. The disease has been present in the country since the mid-1980s without exploding and the rate of growth of new infections is now slowing. According to Meenakshi Datta-Ghosh, head of Naco: "There is no galloping Aids epidemic in India and there is no evidence of an upsurge in HIV prevalence in any state."
Yet on the other hand, many international experts on the disease and non-governmental organisations working in the country on the issue say India is stepping very close to a massive Aids problem.
"India is the ticking time-bomb of the global Aids pandemic," says Richard Feachem, executive director of the Global Fund to Fight Aids, Tuberculosis and Malaria, the UN-sponsored organisation that finances programmes for the three diseases. "It is not too dramatic to say that if there is a major epidemic in India, the global prevalence of Aids will continue to rise throughout the first half of the century."
Ashok Alexander, an Indian who runs the Bill and Melinda Gates Foundation's office in India, is equally concerned: "I do not want to sound alarmist, but when are we going to realise that this is something that could turn out to be a huge threat to India's development?" The Gates Foundation is putting $200m into Aids prevention in projects in India over the next five years.
The basic figures can be used to support both views. The overall prevalence of the disease in India is less than 1.0 per cent of the population, the level that is the first warning sign of a significant problem. However, because of the sheer size of India's population, a relatively low percentage can still involve huge numbers. The 5.1m people in India who are now infected with HIV puts it second behind South Africa. One in seven people with the virus are now in India.
Moreover, the national figures mask some startling situations in certain regions. There are districts with populations of several million people where infection rates are more than 4.0 per cent -- a clear sign that in those areas at least the disease has already spread beyond high-risk groups into the general population.
As Alexander points out: "At some stage there is a tipping point of critical mass beyond which the disease escalates rapidly." It does not take an epidemic on the scale of southern African -- where infection rates are more than 30 per cent in some countries -- for there to be tens of millions of people in India with the virus, he says.
There is another reason why India is the cause for such alarm among health experts: virtually all the factors that have been behind the growth of the disease in African countries are present in abundance in India.
Brian Brink, who runs the Aids programme for South African mining group Anglo American and who has been involved in work with Aids for many years, recently visited India. "In many ways, it feels a lot like Africa in the 1980s," he says.
Kamatipura in central Mumbai is emblematic because it brings together two types of people who are at the greatest risk of catching the disease and transmitting it to others: prostitutes and migrant workers.
In southern Africa, one reason for the spread of Aids has been the high mobility of the workforce, particularly the men who leave home to work in the mining industry. India, too, has a highly mobile male population. Most attention is focused on lorry drivers who can spend several weeks at a time on the road. Indeed, the early spread of the disease mirrored the main trucking routes in the country.
However, the lorry drivers ate only on part of a much larger peripatetic workforce. It is common for men living in rural areas to move to cities to find work for a few months and then return home once they have earned some money. In Mumbai, they come to work in textiles or construction or as domestic servants and many live in neighbourhoods such as Kamatipura.
Health experts call the phenomenon "the three Ms" -- mobile men with money. Far away from their families, these men visit prostitutes and are infected. They then take the virus home with them and pass it on to their wives.
Ishwar Gilada, a Mumbai doctor who has set up an Aids clinic and a number of prevention programmes, points to the example of taxi-drivers in the city. "Ninety per cent of the drivers come from other states such as Bihar and Uttar Pradesh and they live for part of the year here in cramped accommodation, with up to 10 in one room," Dr Gilada says. "They are very much at risk from Aids."
Another factor that contributes to the spread of the disease is the easy availability of commercial sex workers. Once again, big Indian cities are fertile territory because they often combine huge pockets of desperate poverty with relative prosperity. Prostitution tends to flourish when inequality is pronounced.
Mumbai has an added risk factor that southern Africa does not have -- intravenous drug use. As well as being a transit route for heroin and other drugs grown in neighbouring countries such as Myanmar, India's big cities have become substantial markets for the drugs.
The other big reason that India is causing alarm is the level of denial and stigma surrounding the disease. Although the government has set up Aids awareness programmes, there is still huge ignorance about the virus. According to a survey conducted by Naco, only 19 per cent of women in a rural part of Bihar state believed HIV was transmitted through sex.
"There is more stigma in India over Aids and sex than in southern Africa," says Peter Piot, executive director of UNAids.
Meanwhile, Praful Patel, the World Bank's vice-president for South Asia, early this month accused India's leaders of being "in a state of denial".
This manifests itself in the attitude towards homosexuality. Although heterosexual sex is the principal means of transmitting the virus in India, UNAids officials believe that male-on-male sex is also a significant factor. Yet as homosexuality is illegal, it is difficult to collect any data on the subject, let alone design policies for Aids prevention aimed at such men.
"There is this belief that we are an incredibly moral culture, so that even though we are as sexually active as anyone else, we do not want to acknowledge it," says Anjah Gopalan, head of the Naz Foundation, an Aids advocacy and care group.
Donor governments and non-governmental organisations have become increasingly frustrated with what some view as a complacent attitude at Naco, the government's Aids body. "The problems that I see are bureaucratic delays," says an official from one aid donor in New Delhi. "People who think that Aids is not urgent. People who are not interested in outcomes but building an Aids empire."
In the face of such problems, however, there are growing signs that government and society are engaging with Aids and the various policies that need to be put in place to control the disease. Several state governments have launched aggressive prevention plans including condom distribution, as well as more modest programmes for treating the disease. Last year a parliamentary forum on Aids was held which brought together officials from all over the country to discuss the issue.
Rahul Dravid, the cricketer, has become one of the first celebrities to record a public-service advertisement on Aids, while several television channels are giving free airtimes to messages aimed at preventing the virus.
At the grassroots level there have been noteworthy initiatives which are being copied elsewhere. A group in Mumbai that Dr Gilada helped to found, People's Health Organisation, runs training programmes for prostitutes that teach them to provide advice to their peers on using condoms, on resisting violence and monitoring their health. Dr Gilada believes that the infection rate among sex workers in the city has now stabilised.
Most importantly, there have also been a number of signals that the new government plans to take the Aids issue more seriously. Under the previous BJP-led government, which was highly conservative on a number of social issues, some advertisements for condoms were barred and use of condoms dropped 10 per cent over the last three years. However, the new finance minister, P. Chidambaram, used his recent budget speech to promote "safe sex through the use of condoms". He also promised better surveillance of Aids, more public awareness campaigns and the distribution of disposable syringes.
When Congress was returned to office in May, one of its promises was to deliver substantial improvements in public health. Aids will be a key test. The government now has the chance to marshal the different policies that will be needed to prevent a series health problem from becoming a disaster.