In the early days of AIDS, the disease was referred to by the CDC as the 4H disease, due to their high infection among hemophiliacs, homosexuals, heroin users, and Haitians. The first three groups are susceptible to AIDS via straightforward blood or sex transmission. What caused the Haitian cluster?
In 1983, papers published in the two top medical journals, the New England Journal of Medicine and The Lancet, described the prevalence of AIDS in Haiti. This was the first time the disease was identified in any tropical/developing country. Later the first likely AIDS-related death in Haiti was traced back to July 1978 (source).
However, we now know that the virus was already spreading slowly through the Democratic Republic of Congo from the 1920s through 1950s. There is evidence to suggest that Haitian professionals contracted the virus while working in the Kinshasa area during the 1960s, shortly after Congo's political independence. It is thought that some time after that, the virus arrived in the United States by way of Haiti. The United States in turn became the main source of transmission to the rest of the world, around the same time that AIDS was discovered in 1982 (source).
Beyond this though, it is important to recognize that the "4H" concept has at least as much to do with public awareness and perception as it does with epidemiology. The virus went undetected in developing countries for decades. Haiti's proximity to the United States and the increasing rate of Haitian immigration to the United States during the 1970s and 1980s contributed not only to the actual spread of the disease, but also to the relatively early timing of its discovery there and its stigmatization in the eyes of the majority-white US public.
According to the Centre for Disease Control and Prevention (CDCP):
Haiti has the greatest burden of HIV/AIDS in the Caribbean region with an estimated 150,000 people living with HIV/AIDS, according to UNAIDS 2016 data. While Haiti has a generalized epidemic with most transmission occurring from heterosexual sex, data indicate that drivers of new infections include unprotected transactional and commercial sexual activities as well as unsafe sexual practices among men who have sex with men.
It seems that unprotected heterosexual activity (between men and women and between men and men) is behind the increase of new infections.