What the experts say about the bacteria

A dish of yusheng sold at a hawker stall.
A dish of yusheng sold at a hawker stall. PHOTO: THE NEW PAPER

Q What are Group B Streptococcus (GBS) bacteria?

A They are commonly found in the gut and urinary tract in about 15 to 30 per cent of adults without causing any disease.

But they may occasionally cause infections of the skin, joints, heart and brain. Those who have chronic conditions such as diabetes usually have a higher risk of getting a GBS infection.

Q The GBS ST283 strain has been associated with consuming yusheng, a raw fish dish, but not sashimi so far. Why?

A The reason is still not known but one reason could be that the song, toman and tilapia fish are freshwater fish, whereas most sashimi fish are seawater fish, said senior research scientist Swaine Chen from the Agency for Science, Technology and Research's Genome Institute of Singapore.

Experts have also pointed to cross-contamination as a possible cause.

Q What makes sashimi safe to eat, but not yusheng raw fish dishes?

A Most fish used in Chinese-style raw fish dishes are intended for cooking, and should not be eaten raw.

Fish that are supposed to be eaten raw, such as that for sashimi, are typically bred or harvested from cleaner waters, as well as stored and distributed according to specific cold chain management practices.

This includes transporting them at temperatures below 5 deg C, and packing them independently in a clean and hygienic environment.

Q Can raw meat harbour GBS as well?

A While the ST283 strain has not been looked at in other types of animals, Dr Chen said that the risk from other meats for this particular strain is "very, very low".

Q Will GBS bacteria spread from human to human?

A The bacteria can be transmitted from an infected pregnant woman to her baby during delivery, which can be life-threatening for the baby, said Associate Professor Kevin Pethe, from Nanyang Technological University's Lee Kong Chian School of Medicine.

However, for this strain in particular, the spread from human to human has not happened.

So far, it appears to have spread to humans only via food consumption, said Dr Hsu Li Yang, a consultant in the Division of Infectious Diseases at the National University Hospital.

Q How does the bacteria enter the body?

A The bacteria enter the body through the gut before they go into the blood stream, and cause an infection in the brain, joints or bones, said Dr Leong Hoe Nam, an infectious diseases specialist from Mount Elizabeth Novena Hospital.

Q Why does the GBS strain not affect everyone in the same way?

A In general, people who have weak immune systems or other medical problems have a higher risk of many infections.

Q Were poor hygiene practices of hawkers behind the GBS outbreak earlier this year?

A It is unlikely. The stool samples of 82 food handlers and fishmongers were tested, and none of them was positive for the specific strain of GBS associated with the outbreak.

Q If the bacteria did not come from mishandling by hawkers, where did they originate from?

A There is not enough data to be sure. However, the possibility of them being imported bacteria from fish farms or suppliers overseas cannot be ruled out.

Q Does this mean that hawkers will no longer be allowed to sell Chinese-style raw fish dishes with porridge in the future?

A No. They will be allowed to sell such dishes as long as they are able to show that their fish come from suppliers with a health certificate attesting to their quality.

They must also adhere to all other practices required to sell such fish, such as handling this kind of raw fish separately from other raw products that are going to be cooked.

Linette Lai

Carolyn Khew

A version of this article appeared in the print edition of The Straits Times on November 28, 2015, with the headline 'What the experts say about the bacteria'. Print Edition | Subscribe