Young black men who have sex with men (MSM) face a disproportionate risk of acquiring HIV because of “dense sexual networks” and other structural factors, not high-risk sexual activities, according to a new study conducted by Northwestern University.

The study, which was recently published in the Journal of Acquired Immunodeficiency Syndromes, surveyed MSM in Chicago and found young black MSM in the city are 16 times more likely to have HIV than their white counterparts, despite lower numbers of sexual partners, less unsafe sex and more frequent testing for HIV.

“Our study illuminates how HIV disparities emerge from complex social and sexual networks and inequalities in access to medical care for those who are HIV positive,” said senior study author Brian Mustanski, a professor at Northwestern’s Feinberg School of Medicine and director of its Institute for Sexual and Gender Minority Health and Wellbeing.

“Their social and sexual networks are more dense and interconnected, which from an infectious disease standpoint makes infections transmitted more efficiently through the group,” Mustanski said in a statement shared with NBC News. “That, coupled with the higher HIV prevalence in the population, means any sexual act has a higher chance of HIV transmission.”

Other factors that researchers probed were stigma, victimization, traumatic experiences and sexual abuse. Young black MSM reported the highest rates of these risk factors, which, according to study co-author Michael Newcomb, contribute to the “difficulty in establishing viral suppression.”

Young black MSM, according Newcomb, were also found to be the “most likely to have sex with people of their own race.” This, he added, means “it takes HIV less time to travel around that network, particularly if prevalence is already higher and viral suppression is already lower.” He also noted that there is stark racial and geographical segregation between white and black men who have sex with them in Chicago, which is a contributing factor.

While he Northwestern study looked specifically at Chicago, Mustanski said the higher incidence of HIV among young black MSM can be extrapolated in varying degrees to other parts of the country.

“National data also shows big differences in the rate of HIV diagnosis between black and white young gay men. There are large differences consistently found across different parts of the U.S.,” he explained. “In some cities, it’s three to five times higher; in other cities it’s as much as 20 times higher.”

Mustanski said the difference is particularly pronounced in the South, which is most impacted by new HIV diagnoses. “There is a history of large racial disparities in the South in terms of access to health care, poverty and education,” he said.

In 2016, the Centers for Disease Control and Prevention announced that, if trends were to continue, half of all black gay men will acquire HIV in their lifetimes. But some places, like New York City, have made an impact on HIV incidence in black and Latino MSM populations, even while other places have seen disparities worsen.

Newcomb said this new new study finally provides data to support what had up to this point been a widely held hypothesis: that the dense, segregated sexual networks of young black men who have sex with men are the main drivers of their higher HIV rates.

Ethan Morgan, a postdoctoral fellow at Northwestern’s Institute of Sexual and Gender Minority Health and Wellbeing and another of the study’s authors, said by learning more about young black MSM social networks, “we can better understand what drives such persistent racial disparities in HIV — and close that gap.”

Phill Wilson, president and CEO of the Black AIDS Institute, said he was not surprised by the study’s findings.

“If I am a black gay man and primarily sexually active with other black gay men, that fact alone puts me at higher risk,” Wilson explained. “If I am a white gay man, and I usually protect myself, and in the heat of a night I have an experience, my price for that experience is not the same as the price is if I am a young black gay man.”

Because of “dense sexual networks,” which were pointed out in the Northwestern study, Wilson said a gay black man who “has one slip” by having unprotected sex with another gay black man has a higher chance of a “lifelong diagnosis, and then furthermore, he’s demonized.”

“You have folks who don't have as much information about things like TasP or PrEP or PEP, or even behavioral interventions,” he said, referencing new prevention methods that use HIV medications to eliminate the risk of HIV transmission.

“To be completely honest, the messenger matters, and there’s an infrastructure within black MSM communities,” said Wilson. “We are not going to solve the problem among this population unless and until institutions that are about, and by, and for them are properly, sufficiently supported with infrastructure they need to succeed.”

Wilson pointed to proactive efforts by African-American community organizations like his own as a solution. Since opening a PrEP clinic, the Black AIDS Institute has increased the number PrEP-using black gay men in Los Angeles County by 50 percent, he said.

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