The "possibility of secondary infection" from Singapore's first imported Zika case remains, said the authorities, even though the infected Watten Estate resident has since been discharged from hospital.

In a joint statement released yesterday, the Ministry of Health and the National Environment Agency (NEA) urged the public to remain vigilant until June 23 - the end of a six-week period from the Zika patient's date of isolation.

The 48-year-old permanent resident was confirmed as having the virus last Friday after contracting it during a business trip to Sao Paulo, Brazil.

"Even after June 23, we will still need to remain vigilant for the possibility of new imported cases," the agencies said.

The virus is spread by the Aedes mosquito, which also transmits dengue. Since Wednesday, more than 700 premises have been inspected, with 43 mosquito-breeding habitats detected and destroyed. Most were in homes.

"NEA will continue to keep the area under surveillance... for as long as there continues to be a risk of Zika transmission in the area," a spokesman said.

Ng Huiwen