A pathologist says that one of three children whose sudden deaths led schools to close last year could have died of several causes but it was unclear which was the leading one. Ho Po-yi, a three-year-old girl, died on March 1 with flu-like symptoms, within weeks of the deaths of two other children with similar symptoms. The government shut down all schools as fears rose of an infectious disease. Pathologist Chiao Wing-fu said yesterday when presenting Po-yi's autopsy report that many factors contributed to the girl's death but that he could not determine which was mainly responsible. Po-yi had the H3N2 flu strain, was taking several antihistamines and anti-emetic medicines before she died, and had a myocardial bridge - where a blood vessel runs through muscle instead of outside it - possibly cutting circulation. She had a genetic mutation that research on western patients indicated could cause a condition where the heart sometimes beat irregularly. Asked whether it was comparatively likely that an obscure natural illness had caused an acute irregular heartbeat, leading to death, Dr Chiao said yes. He eliminated injury and poison as possibilities. Po-yi's mother took her to see a doctor on February 29 after she developed a fever and a cough, the girl's father, Ho Kwok-man, said. When her fever persisted, the parents took her to Tuen Mun Hospital at 4am the next day. After a body check showed no abnormalities besides a fever, and a chest X-ray showed no inflammation, the hospital discharged her. Po-yi went to a mall in Tuen Mun, but while there was tired. Her parents took her to her grandmother's home but while travelling there in a taxi, she had difficulty speaking and breathing. When they arrived, at about 4.30pm, she had stopped breathing and they called an ambulance. Wong Oi-fung, a doctor at Tuen Mun Hospital's emergency room, told the inquest that Po-yi arrived at 4.39pm with no heartbeat. Staff gave her 10 adrenaline injections and attempted to resuscitate her, but pronounced her dead at 5.27pm. The Coroner's Court inquest into the three children's deaths, which had already heard evidence about Or Hoi-yeung, two, continues on Monday before Coroner William Ng Sing-wai with testimony on the third child, Law Ho-ming, seven.