"I think one of our largest concerns in Kenya is the large number of people who are addicted to heroin, and many of them are actually injecting themselves," said Jennifer Kimani, who heads up Kenya's National Campaign Against Drug Abuse.
"Among the injecting drug users, 68 to 88 percent are HIV positive," she told the World Forum Against Drug conference in Stockholm.
A clear increase in the number of addicts, she lamented, was threatening to "reverse the gains that our country has actually achieved in the area of controlling HIV and AIDS."
"It's a very worrying situation."
Olawale Maiyegun, the head of the African Union's Social Affairs Department, agreed.
"It is feared that the next round of an HIV/AIDS epidemic might be (prompted) by drug injection," he told the Stockholm conference, lamenting the lack of research into how rampant the drug abuse is.
"We need to look at what the prevalent rate is," he said.
An increase in other forms of substance abuse, especially cannabis and legal and illegal alcohol consumption, was also casting a shadow over advances made to rein in the deadly diseases, Kimani said.
"The rising cases of the uptake of drugs and alcohol has led to a higher level of unsafe sex," she said.
The cause of the hike in drug abuse in the region, experts say is that eastern and southern African nations have increasingly become transit countries for the international drug trade.
"The history of society has shown that when you're a transit country, sooner or later it will increase consumption. That is already happening. Africa (provides) transit," Maiyegun said.
According to a report from the UN's Narcotics Control Board from 2008, East Africa has become "the major conduit for smuggling heroin from southwest Asia into Africa (and on to) Europe and North America."
"The abuse of heroin has become a matter of concern in some east and southern African countries," the report added.