It had been thought that the breaks in the skin were the reason for higher HIV rates, but a study last year found that treatment of herpes with drugs did not reduce the HIV risk.
"This is something they have been working on for forever and a day," said Brian Bissett, the editor of the MFP Report, a publication about office printers and copiers.
Although recent years have seen substantial reductions in noxious pollutants from individual motor vehicles, the number of such vehicles has been steadily increasing.
Falling birth rates are also indicators of better educated and more autonomous women, which is one reason why sub-Saharan Africa's birthrate remains stubbornly high.