Maj. Michael O'Connor of the Atlanta Police Department said in February that Cunningham had recently been turned down for a promotion at work, and left feeling ill shortly after his supervisor explained why he'd been passed over.
"Dr. Cunningham's colleagues and friends at CDC hope that he is safe", Burden said. Police said there did not appear to be foul play, but they are awaiting a toxicology screen and other testing results.
Cunningham left work in the Atlanta office on February 12, saying that he was sick after learning he was passed over for promotion.
Authorities said Thursday that a cluster of new HIV infections has occurred largely among the homeless and people who inject drugs.
The Atlanta Police Department, the Fulton County Medical Examiner's Office and the Atlanta Fire Rescue Department will release further details during a news conference Thursday afternoon.
Investigators and Cunningham's family located his personal belongings, including his keys, wallet, cell phone and even his dog, Mr. Bojangles all at his home in Northwest Atlanta.
His death has been classified as a drowning. Cunningham lived near the river where his body was found and was an avid jogger, and he had been wearing a jogging outfit.
Sgt. Stafford said the area where Cunningham was found was inaccessible through walking.
The CDC denied those reports and said Cunningham received an early promotion for his exemplary performance at work.
The 35-year-old had reportedly worked as a commander in the U.S. Public Health Service and had responded to the Ebola virus and the Zika virus outbreaks. It was initially reported that Cunningham may have been upset about not getting promoted, but CDC officials retracted this claim, saying the doctor actually received an early promotion.
However, almost two weeks later, the CDC said that information was untrue.