"However, rest assured, health officials had conducted swab tests on 67 people in the hotel and all were cleared of infection," said Dr. Opas Karnkawinpong, Director-General of the Department of Medical Sciences, Ministry of Public Health.
Seven specimens from the environment in the hotel in Bangkok's adjacent province of Samut Prakan were examined and the virus was found in one of them, he added.
There was a risk of quarantined people spreading the virus in a gym or in other areas of the hotel, he said.
Due to this incident, the ministry's Disease Control Department and the Department of Health Service Support have decided to tighten up preventive measures at hotels used as quarantine facilities.
Regarding the infected case, a French woman, Opas said that the latest blood test showed no sign of antibodies, while her husband, son and a friend who picked her up at Samui airport have been cleared of the virus.
All 10 passengers on the same flight with the woman from Bangkok to Koh Samui, and two cabin crew, have been tested with negative results and all have been isolated for observation.
The 57-year-old woman entered quarantine at a hotel in Bangkok on Sept 30 after her arrival from France.
She underwent two tests during the 14-day mandatory quarantine period, which both returned negative results.
Two days later she fell ill, with a fever, cough and muscle pain, and was admitted to a private hospital on the island. Two subsequent tests confirmed she was infected.
Thailand on Sunday reported four new coronavirus cases, including the women and three others identified whilst in state quarantine, taking the total number of infections to 3,736.- Xinhua