HANOI, Vietnam (AP) -- Vietnam has asked international health experts to help investigate a mystery illness that has killed 19 people and sickened 171 others in an impoverished district in central Vietnam, an official said Friday.

The infection has mostly affected children and young people. It begins with a high fever, loss of appetite and a rash that covers the hands and feet. Patients who are not treated early can develop liver problems and eventually multi-organ failure, said Le Han Phong, chairman of the People's Committee in Ba To District in Quang Ngai province.

Nearly 100 people remain hospitalized, including 10 in critical condition. Patients with milder symptoms are being treated at home. The illness responds well to treatment if detected early, but 29 patients have been reinfected, Phong said.

The Ministry of Health sent a team of health officials to the area earlier this month, but they were unable to determine the cause of the illness. The ministry has since asked the World Health Organization and the U.S. Centers for Disease Control and Prevention to help investigate.

The ailment was first detected last April, but the number of cases had died down by October. A fresh spate of infections started last month, with 68 cases and eight deaths reported between March 27 and April 5, Phong said.

Most of the patients are from Ba Dien village in Ba To. It is one of the poorest districts in the province and home to many of the Hre ethnic minority group.