(AP) -- Vietnam's prime minister has put the country on alert as an outbreak of hand, foot and mouth disease continues to surge, killing 81 children and sickening more than 32,000 people nationwide so far this year, officials said Friday.

Prime Minister Nguyen Tan Dung has called for stepped-up efforts to prevent and control the transmission of the common childhood disease. It has spread nationwide but is raging hardest in the country's south, where nearly 80 percent of the cases have been reported. About 65 percent of the deaths have occurred in children younger than 3.

"Hand foot and mouth disease, a dangerous infectious disease for children under 5, is spreading fast, creating huge danger to the health and life of young children," Dung said in a statement that appeared on the government's website Friday.

This year's outbreak is a sharp increase over previous years. Since 2008, about 10,000 to 15,000 cases were reported per year, with about 20 to 30 children dying annually.

Hand, foot and mouth disease is spread by sneezing, coughing and contact with fluid from blisters or infected feces. It is caused by a group of 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 telltale symptoms it causes, including rash, mouth sores and blisters covering the hands and feet. Many infected children are not sickened at all, but remain capable of spreading it to others.

A more severe strain called enterovirus 71, or EV-71, has been identified in about a third of the sampled cases in Vietnam, said Dr. Graham Harrison, the World Health Organization's acting country representative for Vietnam. EV-71 can result in paralysis, brain swelling and death.

Harrison urged greater awareness at clinics and hospitals outside cities in detecting and treating new cases. Early symptoms include fever and sore throat, with the rash and blisters coming later in most, but not all, patients.

He said there's been a slight decrease recently in the number of cases, but it's too soon to know for sure whether the outbreak is waning. State media have reported about 2,000 new cases are still being logged every week.

"It started picking up in May or June like it had in previous years," Harrison said. "Whether it's going to go down and come back up or has just sort of peaked for the year and will then go down, we'll have to wait and see."

Dr. Truong Huu Khanh, head of the infectious disease department at Ho Chi Minh City's main children's hospital, said the number of patients has decreased compared to a month ago. He added that most children being admitted are now coming from southern provinces outside the city.

WHO is assisting with the outbreak along with the U.S. Centers for Disease Control and Prevention. They are urging enhanced hygiene, including frequent hand washing and regularly cleaning floors, tables and counters with disinfectant.

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