Hong Kong health authorities have identified 21 people showing mild symptoms of chikungunya fever who required blood tests, as the city’s leader pledged that his administration would go all out to prevent the viral disease from taking root locally.

The Centre for Health Protection on Tuesday also said the source of infection in a 55-year-old woman confirmed with the mosquito-borne illness a day earlier was still under investigation, but a genome analysis was being conducted.

The centre said it had assessed about 2,100 residents between Sunday and 5pm on Tuesday through a hotline and a medical booth set up at the Fung Tak Shopping Centre, located in the public housing estate linked to the city’s first local chikungunya infection.

Among those assessed, 21 residents displayed mild symptoms, and were arranged to undergo blood tests.

“Laboratory testing is continuing,” it said. “So far those samples that have completed testing are all negative for chikungunya virus.”

Chikungunya fever is a viral disease transmitted by the Aedes aegypti mosquito, with an incubation period of about two to 12 days. Although rarely fatal, it can cause fever, rash, and joint pain.