Health authorities in China are continuing to monitor 37 people for bird flu symptoms.

The measures follow the discovery of bird flu on a chicken farm in Anhui province earlier this week, reported the China Youth Daily. All workers who might have come into contact with the infected birds are being given daily temperature checks. As yet none have shown any symptoms.

Four months ago China announced it had wiped out bird flu, so this week’s discovery was disappointing. Officials have called it an isolated event and suspect waterfowl or migrating birds as the cause.

Thailand and Vietnam have also reported new outbreaks of the severe strain of avian flu virus that devastated flocks earlier this year and jumped to people in those two countries, killing 24, reported AP.