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2015 infections after eating raw fish linked to little-known, highly infectious strain of GBS bacteria: Researchers

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Wednesday, July 10, 2019

SINGAPORE - In 2015, a highly infectious bacteria strain caused an outbreak of blood poisoning in more than 160 people in Singapore, who suffered from fever, joint infection and meningitis after eating hawker dishes containing raw freshwater fish.

One of the victims, a 50-year-old man, lost all of his limbs, and another, a 54-year-old man, fell into a two-week-long coma in the largest outbreak of its kind in the world.

Now, researchers led by Tan Tock Seng Hospital have discovered that the Group B Streptococcus (GBS) bacteria causing the disease was a hitherto unflagged strain - GBS ST283 - that has caused disease in humans and freshwater fish mainly in South-east Asia for more than two decades.

Using DNA analysis of invasive Asian collections dating back to 1995, researchers found that the ST283 infections occurred in Laos, Thailand, Vietnam and Singapore. While most GBS strains do not cause disease in healthy adults, ST283 turned out to be especially virulent, accounting for 76 per cent of human GBS in Laos, 73 per cent in Thailand, 31 per cent in Vietnam and 23 per cent in Singapore.

"Our research reveals a previously unknown disease pattern that has escaped detection," said the principal lead investigator of the research, Dr Timothy Barkham, senior consultant medical microbiologist at TTSH's Department of Laboratory Medicine.

The researchers also found that between 2007 and 2016, the strain infected tilapia at 14 fish farms in Malaysia and Vietnam.

In the 2015 outbreak in Singapore, customers fell ill from eating seven species of freshwater fish, including tilapia, carp and snakehead.

The alarming rate of illness prompted the Government to ban hawker stall owners from selling raw freshwater fish. Following the ban, the infection rate dropped. The bacteria has not been found in saltwater fish, such as those in Japanese sashimi.

The research team, which comprised a network of 30 collaborators, published these findings in the peer-reviewed scientific journal PLoS Neglected Tropical Diseases earlier this year.

Very little is known about GBS ST283 and Dr Barkham said cross-border collaborations in animal and human health are urgently needed to complete the picture so that its transmission can be understood and halted.

Although their analysis showed 1 per cent of the seven freshwater fish species were infected with ST283 at the ports here, 28 per cent of the fish were infected by the time they reached the markets. This suggests that contamination during transport and handling could have amplified the spread of the bacteria, the study said.

The research team is working with the Agency for Science, Technology and Research's Genome Institute of Singapore to determine the bacterial strain's origin, spread, transmission and extent of harmfulness.

It also said Singaporeans should heed the Government's advisory not to consume ready-to-eat meals containing raw freshwater fish, and avoid consuming raw or undercooked fish when they travel to neighbouring countries.

Source: straitstimes
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