The authorities are looking into a recent spike in bacterial infections that were associated with eating raw freshwater fish in the past.
In a Friday circular to doctors seen by The Sunday Times, Ministry of Health (MOH) medical services director Kenneth Mak said 50 cases of invasive Group B Streptococcus (GBS) were reported by public hospitals last month - twice the average monthly figure of 25 from earlier this year.
Laboratory tests showed 18 of these cases were infected by GBS Type III ST283, and the profile of these patients is similar to those who were infected by the same bacteria in a 2015 outbreak caused by eating raw freshwater fish.
Among the latest 18 cases, most were aged 65 years and above who developed septicaemia or bacteraemia, commonly known as blood poisoning. All of them were Chinese, said Associate Professor Mak in the circular.
Most of the patients have been discharged but one patient died from an unrelated cause.
"All medical practitioners are requested to remain vigilant and to refer all patients with symptoms suggestive of severe GBS to a hospital for assessment," said Prof Mak.
It is not known if the July infections are linked to eating raw freshwater fish. ST has contacted MOH and the Singapore Food Agency for more information.
In 2015, the highly infectious strain of GBS caused an outbreak of blood poisoning in over 160 people, who suffered fever, joint infection and meningitis. GBS is a common bacterium found in the human gut and urinary tract of about 15 per cent to 30 per cent of adults without causing disease, said Prof Mak. It may occasionally cause serious infections and symptoms include fever, chills and low alertness.
Doctors confirmed with ST yesterday that they had received the circular and warned that the disease could be easily misdiagnosed as Covid-19 or dengue fever.
Dr Leong Hoe Nam, an infectious disease specialist at Mount Elizabeth Novena Hospital, said this is because the initial symptoms are "remarkably similar".
"You don't want to put a strain on the existing system, already laden with Covid-19 and dengue... It confuses the picture," he added.
He said he has seen at least three GBS cases in recent weeks, and that 50 cases was a lot, considering milder cases may not be identified.
Similarly, Dr Raymond Ong, a general practitioner at Intemedical 24 Hour Clinic, said the symptoms are the same as with many other infections. As is the case with Covid-19 and dengue, most people recover, but GBS infection is more dangerous for the elderly and those with pre-existing conditions, he added.
Some senior citizens ST spoke to were worried but added that they no longer consume raw food.
Ms Laura Chia, 70, who was dining at Yishun Park Hawker Centre yesterday evening, said she stopped eating raw food because of contamination fears and a health scare after eating contaminated seafood on holiday.
"My favourite used to be this porridge stall in Maxwell (Food Centre), which also served raw fish. But they closed some years ago, and I've also stopped," she said.
The authorities banned the sale of such ready-to-eat freshwater fish by retail food places after the 2015 GBS outbreak.
A Hougang resident who wanted to be known only as Mr Lau, 77, was concerned that the recent infections could be due to contamination while handling food.
"When I was younger, I still ate raw food. Now, at my age, it is very risky to touch things that are not fully cooked," said the retiree, a former factory owner.
Doctors stressed the importance of hygiene in food preparation and consumption. Dr Ong said: "The disease is transmitted through the faecal-oral route, so hand hygiene is very important." He advised consumers to wash their hands and not to cross-contaminate cooked and uncooked food.
Dr Leong agreed, saying: "If we don't clean food with GBS, we end up as food for the GBS."
2015 outbreak led to ban on sale of ready-to-eat raw freshwater fish
In 2015, there was a mass outbreak of 360 infections caused by the Group B Streptococcus (GBS) bacterium.
Two died from the infection.
About 160 of those infected had blood poisoning caused by a much more infectious strain of the bacteria - GBS ST283 - linked to the consumption of raw freshwater fish.
They suffered from fever, joint infection and meningitis.
Tests conducted by the authorities on nearly 400 fish samples concluded the strain was found in Toman fish, also known as snakehead fish; Song fish, also known as Asian bighead carp; and tilapia. The first two types are often used in Chinese-style dishes with raw fish.
The public health scare prompted the Government to ban food retail establishments from selling ready-to-eat raw freshwater fish in December 2015. The bacteria has not been found in saltwater fish.
Infection rates dropped after the ban, which is still in place.
In July last year, researchers led by Tan Tock Seng Hospital and the Agency for Science, Technology and Research found that the ST283 strain has caused disease in people and freshwater fish mainly in South-east Asia for over two decades, and is especially aggressive.
By analysing the DNA of bacteria samples collected from local hospitals dating back to 1995 and regional data, researchers found that over 350 ST283 infections have occurred in Laos, Thailand, Vietnam, Singapore, Malaysia and Hong Kong. The ST283 strain is almost completely absent elsewhere. Infections caused by it can be treated with antibiotics such as penicillin.
What is GBS?
Group B Streptococcus (GBS) is a common bacterium found in the human gut and urinary tract of about 15 per cent to 30 per cent of adults, without causing any disease.
It may occasionally cause serious infections like bacteraemia and sepsis, which could be fatal.
Other symptoms include fever, chills and, more seriously, infection of the joints, the brain, the lungs or other soft tissue. A particular strain - GBS ST283 - is linked to eating raw freshwater fish.