It is now known that both stalls in the Geylang Serai Temporary Market shared the same refrigerator. The rojak sellers also used their neighbour's premises to store and wash their equipment.

A joint statement from the Health Ministry and National Environment Agency (NEA) said a food handler at the mee siam stall has been referred to the Communicable Disease Centre for screening. As for the five Indian rojak sellers, three have cleared tests while results for the other two are pending.

It is becoming increasingly certain from further laboratory testing that the Vibro parahaemolyticus bacteria is the source of the food poisoning, 'most likely due to cross-contamination of rojak and raw seafood ingredients harbouring the bacteria,' said the statement.

At last count, 154 people have been struck after eating the stall's Indian rojak, with 48 people warded. Six patients remain in hospital.

The outbreak was cited as an example of deteriorating hygiene standards by Health Minister Khaw Boon Wan yesterday.

He gave Singapore a close to a 'fail' grade on matters of hygiene, compared with the nine in 10 points during the 2003 Sars virus outbreak.

Complacency has set in, he told reporters at a Health Promotion Board event, referring to the state of public toilets today as another example.

He suggested stepping up the frequency of spring-cleaning at hawker centres. NEA guidelines state that this should take place two or three times a year.

The Geylang Serai market was closed for two days for cleaners to wash the area and stallholders to scour their stalls. Pest controllers have been laying traps and baits since last Friday to rid the area of rats.

Read the full story in Friday's edition of The Straits Times.