BEIJING (AP) — A viral outbreak in eastern China has sickened almost 1,200 children, killing 20 of them, health officials said Monday.

Enterovirus 71 infections were discovered in March in Fuyang, a city in Anhui province, but may have gone undetected for a while because the symptoms appeared to be ailments common in children, said Feng Lizhong, an official at the Anhui public health bureau.

Hospitals in Fuyang started to take in patients with fever, blisters, ulcers in the mouth, or a rash on their hands and feet, the official Xinhua News Agency said.

Most were under 2 years old and none was older than 6, Xinhua said.

There were 1,199 reported cases between early March and Sunday, 20 of which were fatal, the health bureau said in a statement on its Web site.

Some 371 children were still being treated and more than 550 had recovered, it said.

It was not immediately clear what triggered the outbreak, but the bureau said it is the season when the virus is prevalent.

Enterovirus 71 is one of several viruses that cause hand, foot and mouth disease, which is characterized by fever, mouth sores and a rash with blisters. It is spread by direct contact with nose and throat discharges, saliva, fluid from blisters, or the stool of infected persons.

The illness mainly strikes children below age 10 and is not related to foot and mouth disease, which infects cattle, sheep and swine.

The World Health Organization’s Beijing office said there didn’t appear to be an epidemiological link among the cases although most of the children lived in rural areas.

“We believe the situation is still of concern, especially because of the current high reported case fatality rate compared to previous years,” said Dr. Cris Tunon, the acting China representative.

The number of cases of hand, foot and mouth has been on the rise in China.

Last year, Beijing reported more than 1,000 cases in the first six months. In the eastern province of Shandong, 1,200 children were infected in May.