Four students and a school teacher are among the 20 community cases announced yesterday.
The students are from Bedok View Secondary School, East Spring Primary School, Jurong West Primary School and Jurong West Secondary School, while the teacher is from Assumption Pathway School, the Ministry of Education (MOE) said in a statement yesterday.
The four students are linked to household infections and were on home quarantine order before they later underwent a swab test as close contacts of their household members.
They were well when they were last in school the previous week, said the ministry.
Investigations are under way for the teacher.
MOE said that beyond existing safe management measures, the affected schools have implemented additional precautions, including thorough cleaning and disinfection of school premises.
For Bedok View Secondary School, MOE said that since the student was last in school on June 30, the Ministry of Health (MOH) has assessed the risk of infection for students and staff to be low and no leave of absence or home quarantine order has been issued.
But about 60 students and 10 staff each from the other four schools who were in contact with the confirmed cases have been issued a 14-day leave of absence by MOE or home quarantine order by MOH.
Among the 20 new community cases yesterday are three Singaporean children: a two-year-old boy, a nine-year-old girl and an 11-year-old boy.
The two younger children are contacts of a previously announced patient - a 29-year-old Indonesian woman who tested positive last Thursday - and were confirmed to be infected with Covid-19 on Monday.
The 11-year-old boy is a contact of another previously announced patient.
Update on cases
New cases: 157
Imported: 3 (1 work pass holder, 2 dependant's pass holders)
In community: 20 (10 Singaporeans, 2 PRs, 3 work pass holders, 5 work permit holders)
In dormitories: 134
Active cases: 4,112
In hospitals: 219 (1 in ICU)
In community facilities: 3,893
Patients with Covid-19 who died from other causes: 12
Total discharged: 40,990
Discharged yesterday: 285
TOTAL CASES: 45,140
Twelve of the community cases are linked to previous cases or clusters, while eight cases are currently unlinked.
The ActiveSG gym at Jurong Lake Gardens, the StarHub outlet in Tampines Mall, as well as Great World City, Jurong Point, FairPrice Hub and JEM, are among places visited by Covid-19 patients while they were still infectious, MOH said.
There were three imported Covid-19 cases yesterday.
They are two Indian nationals who are dependant's pass holders, and had returned to Singapore from India on June 23, and a Filipino work pass holder who had returned to Singapore from the Philippines on June 19.
All three had been placed on 14-day stay-home notices upon arrival in Singapore, and had been tested while serving the notices.
Migrant workers living in dormitories made up the remaining 134 cases yesterday, taking Singapore's total to 45,140.
The average number of new cases in the community per day has increased to 14 in the past week, from eight in the week before that.
The average number of unlinked cases in the community per day has increased to six in the past week, from four in the week before that.
A total of 219 patients remain in hospital, including one in the intensive care unit, while 3,893 are recuperating in community facilities.
With 285 cases discharged yesterday, 40,990 patients have fully recovered from the disease.