The terrible prediction, made by the UN's International Labour Organisation (ILO) on Sunday, could inflict a body blow to national economies.
The ILO published its analysis on the opening day of the 15th International Aids Conference, the top forum on the 23-year-old epidemic.
"HIV/Aids is not only a human crisis, it is a threat to sustainable global, social and economic development," ILO Director-General Juan Somavia said.
"The loss of life and the debilitating effects of the illness will lead not only to a reduced capacity to sustain production and employment, reduce poverty and promote development, but will be a burden borne by all societies, rich and poor alike."
Their study, entitled HIV/Aids and Work, Global Estimates, Impact and Response, examines the effects of the disease in 50 countries.
Forty of them had an estimated prevalence of the human immunodeficiency virus of more than two per cent in 2001; five were between 1.5 and 2%; and five were countries with an HIV-infected population of a million or more.
Thirty-five were from sub-Saharan Africa; eight from Latin America and the Caribbean, five were from Asia, and two were from developed countries.
As of today, about 36.5 million people of working age - defined as between 15 and 49 years - have the Aids virus, the report said.
"This loss in human capital is a direct threat to the Millennium Development Goal of reducing poverty and promoting sustainable development"
Franklyn Lisk, director of ILO's Aids programmes
By 2005, the death toll of workers from Aids since the disease was first uncovered in 1981 will be as many as 28 million, the ILO said.
Two million people of working age will be unable to work by next year, compared with half a million in 1995.
Almost five million people of working age in Asia have HIV, the ILO said, referring specifically to Cambodia, China, India, Myanmar and Thailand, the five Asian countries included in the study.
"By causing the illness and death of workers, the HIV/Aids epidemic reduces the stock of skills and experience of the labour force," Franklyn Lisk, director of the ILO's Aids programmes.
"This loss in human capital is a direct threat to the Millennium Development Goal of reducing poverty and promoting sustainable development."
The figures contrast with the toll issued last Tuesday by the UN agency UNAids, which in a report that revised downwards its previous estimate of 2002 said "over 20 million" people of all ages had died of Aids.
The ILO report said Aids was already being felt in macroeconomic terms.
In countries where the impact was measurable, Aids deaths among the workforce clipped 0.2% off the annual rate of growth of gross domestic product between 1992-2002.
This was equivalent to $25 billion a year.