The four centres named on Wednesday are located at Blocks 210, 270, 290A and 298B Sengkang Central.
On Thursday, the PCF spokesman said that children at two other centres located at Blocks 262A and 208 Sengkang Central, as well as the PCF Sparkletots pre-school at Punggol North, have displayed symptoms of food poisoning.
This brings the total number of centres with affected children to seven.
The Ministry of Health also announced that, as of 4pm on Wednesday, the number of reported cases had risen to 184, up from 109 previously.
Nine of the cases are in a stable condition in hospital.
The spokesman said that PCF is in close contact with the parents of affected children, and is monitoring their children’s condition.
PCF will continue to provide the relevant support for all affected parties, he added.
On Wednesday, the pre-school operator said a total of 11 centres were served by Kate’s Catering, the caterer which provided the food linked to the outbreak in the first four centres.
PCF is continuing to monitor the situation in four other centres, and is assisting the authorities with the investigation.
It also suspended the caterer’s services at all 11 centres for an indefinite period of time, and arranged for meals to be provided by a certified in-house cook for the time being.
The authorities were notified of the first cluster of cases last Friday, and conducted an inspection of the caterer’s premises on the same day.
On Monday, however, additional clusters of cases were reported, prompting the National Environment Agency (NEA) to instruct Kate’s Catering to suspend its operations with effect from Tuesday, pending investigations by the Agri-Food & Veterinary Authority of Singapore (AVA), MOH and NEA.
A version of this article first appeared in The Straits Times.