In the next 30 years, Sub-Saharan Africa is likely to see a more than 200 percent increase in the number of older people living with HIV.
"The proportion of people living with HIV aged 50 and over is going to increase a lot," Robert Cumming of the school of public health at the University of Sydney told a conference on ageing in Africa.
Three million people aged 50 or older currently live with HIV and that figure is expected to rise to 9.1 million by 2040.
"It's mainly driven by the fact that people are being treated with antiretroviral drugs and therefore will survive to be old," Cumming said.
But the number of older people living with the disease and without treatment is also expected to rise. That has doctors and other health professionals worried.
"It's a huge problem that is being ignored. It's a huge problem for the older people themselves who are often going to miss out on treatment so they are going to die sooner than they should otherwise do," said Cumming.
Guiseppe Liotta of the University of Rome said many patients in Africa arrived for treatment when very sick, and often with other diseases and conditions like malnutrition and anaemia, but that HIV-caused deaths fell a year into treatment.
"HIV positive elderly would need special attention because they seem to start ARV treatment very late," said Liotta.
An analysis by HelpAge International found only 68 of 119 country progress reports submitted to United Nations agency UNAIDS had some data or reference to older people. Only four had details on prevalence for those living with HIV.
"The lack of data just means we don't have a clear picture of what's happening in relation to HIV and ageing and that means that we can't respond appropriately," said the NGO's Rachel Albone.
Anti-AIDS data and policy efforts in Africa have overwhelmingly focused on the 15- to 49-year-old grouping.
Older people know less about the disease and are less likely to be tested, and face difficulties with access to care, said Cumming.
"I guess it's reasonable to focus on young people because that is where most new infections occur. But there seems to be an attitude that people over 50 don't have sex and therefore can't get infected and that's clearly incorrect."
According to UNAIDS, access to treatment in sub-Saharan Africa had reached 37 percent in 2009 up from two percent seven years earlier.