Food poisoning cases have spiked among those who ate certain raw fish dishes here this year.
We look at a possible culprit, the Group B streptococcus (GBS) bacteria.
What is it?
GBS bacteria are commonly found in the gut and urinary tract of 15 to 30 per cent of adults without causing any disease, but they may cause infections of the skin, joints, heart and brain.
There is a possible link between raw fish consumption and GBS infection, the Ministry of Health (MOH) said last month.
Types of fish
Song fish (Asian bighead carp)
It is highly esteemed for its head region. It has been imported usually as young fish to be cultivated or to be grown out in mud ponds for aquaculture and for food fish purposes
Types of food
Song and toman fish are usually sold as yusheng, a raw fish dish. It is sold at hawker centres as thin slices of raw fish mixed in sesame oil and topped with ginger and chilli.
What experts say
How is the current outbreak of GBS different from earlier ones?
Dr Leong Hoe Nam, an infectious diseases specialist from Mount Elizabeth Novena Hospital: Newborn babies and those with poorer immunity, such as those who have diabetes, cancer and HIV, are usually more vulnerable to the infection, but the current outbreak is afflicting young adults and the old.
Put simply, it is the same bacterium – same soldier – but one that causes more damage.
We are used to the mild ones. Now we are getting hit by the terrorist equivalent.
How does the bacteria invade the body?
Dr Jolene Oon, associate consultant, Division of Infectious Diseases, National University Hospital: GBS is commonly found in the body without invading the blood to cause disease.
Occasionally, however, the bacteria may move, into the bloodstream to later enter joints, the brain or heart, causing infection.
Why does GBS bacteria have the potential to become so serious?
Dr Oon: Any bacterial infection that invades the body can be serious. Invasive disease can happen in healthy young and middle-aged adults as well, but this is rare.
It can cause severe infections of the blood (bacteraemia), joints (septic arthritis), brain (meningitis) and heart (infective endocarditis).
Why is it that GBS bacteria affect fish species, in particular, the snakehead and Asian bighead carp?
Dr Leong: Bacteria, unlike viruses, are less species specific.
For example, the human immunodeficiency virus (HIV) can be found only in monkeys and humans, but not pigs, mosquitoes or rats.
Bacteria, however, can work on different animals and are not species-specific. GBS has been identified in other fish, especially the tilapia fish, so it has a predisposition to affect fish.