"contributing to the spread" is correct and usable in written English.
You can use it when you are trying to refer to something that is having an effect on the proliferation of an idea, situation, or phenomenon. For example, "The rise in technology has been contributing to the spread of new knowledge and skills."
But he doesn't mention one significant factor contributing to the spread of H.I.V.
There are myriad factors contributing to the spread of H.I.V. and AIDS among blacks.
Nyerere R. Mashaushi, who helps run Kambora, a weekly paper, does not see himself as a pornographer or the paper as contributing to the spread of AIDS.
The latest disturbing news is that Myanmar's booming heroin trade is contributing to the spread of AIDS in nearby countries, notably India, China and Vietnam.
The bank is also seen as contributing to the spread of China's "soft power" in the region, possibly at the expense of the United States.
Rising temperatures may already be contributing to the spread of some diseases, like chikungunya, a mosquito-borne virus that, not long ago, was confined to Africa and Asia.
Globally, warming is widely thought to be contributing to the spread of malaria and dengue, each carried by mosquitoes, to high altitudes in Africa and Central and South America where the diseases had not occurred before.
Several trends are contributing to the spread of tuberculosis in Japan, including an aging population, a weak economy that has aggravated the health problems of the poor and widespread ignorance about the long-forgotten disease.
In his book, Mr. Tierney made assertions or strongly implied that in 1968, a prominent anthropologist and a respected medical geneticist inoculated the long-isolated Yanomami Indians with a measles vaccine, contributing to the spread of a deadly epidemic.
The document stated that a number of factors were contributing to the spread of jihadist ideology, including the "cause célèbre"—as the authors called it of the Iraq war.
Parents who shun vaccines, patients who demand antibiotics for every sniffle, farmers who use penicillin to fatten their cows and people who wash with antibacterial soaps are all contributing to the spread of disease and the emergence of dangerous, drug-resistant germs, researchers said today at a press briefing on infectious diseases held by the American Medical Association.
