As Singapore continues to reopen its economy, more people are out and about, adding to the list of places visited by those with Covid-19.

How do I know which places were most visited by Covid-19 cases in the past month?

The Ministry of Health (MOH) provides a daily list of places visited by Covid-19 cases for at least half an hour, for the past 14 days. The timings are also stated. The locations are updated on a rolling basis and the full list is available on the gov.sg website. Close contacts are also notified. There is no need to avoid these places as they would have been cleaned.

How long is this list?

In the last five weeks, those infected with Covid-19 visited more than 90 places, though it is not stated if the same person visited multiple locations. Shopping malls were the most visited, including 12 along Orchard Road and over 30 in estates like Joo Koon and Pasir Ris.

Markets and hawker centres also feature on the list, for example, Old Airport Road Food Centre & Shopping Mall, and Chinatown Complex Food Centre.

The following locations had the most number of repeated visits: Block 4A Jalan Batu Hawker Centre (10), Lucky Plaza (six), VivoCity (five), Geylang Serai Market and Food Centre (four), Wisma Atria (three), Bugis Junction (three), HomeTeamNS Khatib (three), and Bukit Panjang Plaza (three).

What should I do if I visited these places at the times stated on the list?

Monitor your health closely for two weeks from the date of your visit.

If you have a fever, lose your sense of taste or smell, or develop symptoms of acute respiratory infection, such as cough, sore throat and runny nose, see a doctor promptly. Inform the doctor of your exposure history.

Should I avoid the places listed?

It is safe to visit these locations. Research shows that the risk of infection through fomites is low, said Professor Teo Yik Ying, dean of the Saw Swee Hock School of Public Health at the National University of Singapore. Fomites are objects that are likely to carry the virus, for example, furniture. Prof Teo added that the main mode of transmission is still through droplets as a result of human-to-human interactions in close proximity.

All the places in the MOH's list have to be thoroughly cleaned and the work done under the supervision of the National Environment Agency's (NEA) officers. The NEA has guidelines on how the cleaning and disinfection should be done. To date, NEA officers have attended to more than 3,500 premises, the majority of which are residences of the confirmed cases.

How extensively are the premises cleaned?

The NEA's guidelines comprise 22 recommended steps. These include the appropriate temperature for linen to be washed at, and instructions on how to dispose of personal protective equipment donned by the cleaners.

If premise owners and operators are not able to carry out the cleaning themselves, the NEA has a list of companies that they can engage.

A spokesman at one such company, Clean Lab, said that its cleaning team arrives about one to two hours after it has been engaged for a cleaning job. Clean Lab has a crew of three to five trained specialists, who respond only to Covid-19 decontamination requests.

Other companies like Aardwolf Pestkare and Exceltec Property Management said that they use active ingredients recommended by the NEA in the disinfectant solutions for wiping down commonly touched surfaces and misting hard to reach spots.

Besides cleaning, businesses like Muji and Prive restaurant also checked on the health of their staff after finding out that their premises had been visited by Covid-19 patients.

A spokesman for Prive said it "quarantined all relevant staff" upon finding out that its outlet at Wheelock Place was visited.

SportSG said that it typically closes facilities that have been visited by patients for cleaning for one day.

Is cleaning still needed if restaurant, shop and mall operators find out that their premises have been visited by Covid-19 patients only several days after the visit?

Given that locations are updated on a rolling basis, and some time is needed for epidemiological investigations and contact tracing to be done before new places are added to the MOH's list, some premise owners may find out they were visited by patients only up to 14 days after the day of the visit. For instance, eight visits to various locations on Aug 24 were added 14 days after they were visited.

Prof Teo said: "The Sars-CoV-2 virus can survive on surfaces for up to days, and studies have even shown a viable lifetime of up to three weeks in chilled environments of around 4 deg C.

"So it certainly is still good practice to perform the disinfection protocols."