The A/H1N1 mass infection involving 17 pupils in a Beijing primary school was caused by a housekeeping servant, an official with the Beijing Health Bureau said late Thursday.

The unnamed servant began to work for the family of a primary school student at South Lake Park Primary School in the eastern Chaoyang District, on June 25, said Fang Laiying, director of the municipal health bureau.

The pupil, the first to be infected at the school, went to school on June 25 and began to have flu symptoms the same day. The child was taken care of by the grandpa, who was also confirmed to be A/H1N1 positive later, Fang said.

Other pupils began to have the symptoms two or three days later.

The servant had been tested positive to A/H1N1 flu virus and was considered to have recovered without treatment, Fang said.

Fang said that the servant had worked for an unnamed American couple before working for the family. Fang said that the American couple had not had flu symptoms and had returned to their country, but the possibility of their carrying A/H1N1 flu virus could not be ruled out, Fang said. However he failed to present any evidence that they had been infected or had infected the servant.

Beijing Health Bureau published Thursday an open letter to all the parents in Beijing, delivered through their doors or through schools, saying that the students should report to school before they travel outside Beijing municipality limits.

The letter said parents should record all the traveling information and that all those who left the city should remain at home for seven days after return to Beijing.

On Thursday Beijing schools launched measures to avoid mass infection, including health records and temperature measurement equipment.

However mass infection cannot be avoided in Beijing, said the official.

The South Lake Park Primary School was closed after seven students were confirmed as A/H1N1 flu cases Wednesday.

The number rose to 17 as of 8 p.m. Thursday and all the children had been in stable condition.

About 150 students, teachers and parents who had close contact with the patients have been quarantined. Other students and staff are under observation at home.

The primary school has 941 students and 78 teachers.

The flu outbreak has forced the school to start the summer vacation a week ahead of schedule.

The new cases brought the total number in Beijing to 171 by 8 p.m. Thursday, among whom 106 had recovered and been discharged from hospital.

(Xinhua News Agency July 3, 2009)