The reason why there has been a decrease in HIV cases from the late 90's to 2016 is the global campaign for safe sex.
HIV cases around the world have seen a massive decline thanks to public health campaigns that convince people of the need for safe sex.
While safe sex is not a 100% effective, it can result in more than a 90% decrease in HIV transmission which accounts for the drop in HIV cases.
Find out more on HIV rates at https://brainly.com/question/15080938.
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