A deadly form of a common childhood illness has been linked to the mysterious child deaths in Cambodia that sparked alarm after a cause could not immediately be determined, health officials said Monday.

Lab tests have confirmed that a virulent strain of hand, foot and mouth disease known as EV-71 is to blame for some of the 59 cases reviewed since April, including 52 deaths, according to a joint statement from the World Health Organization and Cambodian Health Ministry. The numbers were lowered from the initial report of 62 cases.

EV-71 is a virus that can result in paralysis, brain swelling and death. Most of the Cambodian cases involved children younger than three who experienced fever, respiratory problems that led to rapid shutdown and sometimes neurological symptoms.

Epidemiologists are still trying to piece together information about the cases by interviewing parents because some details may have been omitted or missing from medical charts and specimens were not taken from most children before they died, said Dr. Nima Asgari, who is leading the WHO investigation. Of 24 samples tested, 15 came back positive for EV-71.

"As far as I'm aware, EV-71 was not identified as a virus in Cambodia before," Asgari said, adding that based on the information now available it's likely that the majority of untested patients were infected with it.

"We are a bit more confident. We are hoping that we can come up with something a bit more conclusive in the next day or so," he said.

Telltale rash

Hand, foot and mouth disease has been raging across Asia and usually causes a telltale rash. Blistering was only reported in some of the Cambodian cases, and it's possible that steroids administered by doctors could have masked the symptom or it may not have been recorded, he said.

The lab results also identified other diseases in some cases, including mosquito-borne dengue fever and Streptococcus suis, a germ commonly seen in pigs that sometimes infects people, often causing meningitis and hearing loss.

Hand, foot and mouth disease is spread by sneezing, coughing and contact with fluid from blisters or infected feces. It is caused by enteroviruses in the same family as polio. No vaccine or specific treatment exists, but illness is typically mild and most children recover quickly without problems.

The virus gets its name from the symptoms it causes, including rash, mouth sores and blisters covering the hands and feet. Many infected children don't get sick but can spread it to others.

Neighbouring Vietnam has been battling a surging number of hand, foot and mouth disease cases for the past few years, with EV-71 also wreaking havoc there. Last year, the disease sickened more than 110,000 people and killed 166, mostly children whose immune systems were not strong enough to fend off the infection.

China is also experiencing an outbreak, and more than 240 people have died of the disease there this year, according to China's Health Ministry.

The Cambodia investigation is continuing, but the H5N1 bird flu virus, SARS and Nipah — a deadly virus usually spread by fruit bats or pigs — have all been ruled out.