A Canadian child who doctors previously believed had been rid of HIV has had the virus resurface after going off medication for a short period of time -- an outcome which some researchers are calling a "cautionary tale" for those trying to rid the disease among its youngest victims.

The child is one of five Canadian kids infected with HIV at birth who was treated early and aggressively with combination antiretroviral therapy (cART) in the first 24 hours of life, as well as continued treatment thereafter.

CART is a combination of drugs that helps to keep HIV infections under control. After treatment, researchers say the virus was undetectable in the blood of the five children, and they were reported to be in good health.

But one of the children went off cART at the age of three years and three months, according to new research that was presented Saturday at a medical conference in Newfoundland.

Just two weeks after going off the medication, HIV was found to be present in the child's blood again.

"Soon after stopping the medication, we did start to see signs of the virus back in the child's blood, and that's why we're calling it a cautionary tale," Dr. Lindy Samson, of the Children's Hospital of Eastern Ontario (CHEO), told CTV News.

Doctors say the study – which has not been published in a peer-reviewed medical journal – suggests that HIV can hide a child’s system, even though copies of it cannot be found in their blood.

The virus can hide for a number of years, said Dr. Ari Bitnun, from Toronto's Hospital for Sick Children.

"There can be virus hiding in a single cell or a very few number of cells somewhere in the body, and maybe a year, two years, three years from now, it will reactivate," he said.

For some doctors, the news was a major setback in what had initially been pegged as a possible cure for the virus. But for others, it's additional information that may eventually help to wipe out the disease in its youngest sufferers.

"It’s a step in the right direction," Bitnum told The Canadian Press. "It may be that (the treatment) will work for some babies and it won’t work for others."

He said the results of the latest study add support to a U.S. case where doctors had thought they had "functionally cured" a baby born with HIV.

In 2010, a Mississippi baby born prematurely with a low level of the virus was given a three-drug regimen as treatment.

About three-and-a-half years later, U.S. doctors raised the prospect of a pediatric HIV cure when the child seemed to be virus-free two years after being taken off HIV drugs.

In Canada, doctors have been using a similar approach for a number of years to treat infants born to mothers with HIV.

CHEO's Dr. Jason Brophy’s research group has looked at about 200 Canadian cases where babies were treated for the HIV virus, while trying to determine the best approach for treating babies infected with the virus.

He said in some cases, babies were treated in the first few hours of life, and others would start treatment a few months or years after birth, depending on when the HIV risk was identified,

"Not all children who start treatment at an early stage of infection will be cured," Brophy said.

Meanwhile, according to data from the Canadian Perinatal HIV Surveillance Program, the number of infants born and confirmed to be HIV-infected has decreased gradually over time.

In 2012, there were no documented cases in Canada of vertical transmission of HIV (from mother to infant).

With files from CTV's medical correspondent Avis Favaro and producer Elizabeth St. Philip and The Canadian Press