When his left knee swelled up, he thought it was a muscle pull from cycling.
But when the pain gave him sleepless nights, and bouts of fever started to hit him, Mr Howard Kuay realised it was far more serious.
The 30-year-old tuition agency owner was eventually diagnosed with a Group B streptococcus (GBS) infection.
He had to go through an operation to cut his ligament and move his knee cap to the side to drain the pus out.
And the most likely cause of the infection?
Eating raw fish.
"There is a 99 per cent possibility (of that being the cause)," Dr Leong Hoe Nam, who treated Mr Kuay, told The New Paper.
Mr Kuay eats yusheng (raw fish)only once or twice a year. But after he ate it at a hawker centre last month, he was hit by the GBS infection within a week.
Yusheng sold at hawker centres consists of thinly sliced strips of raw fish drenched in sesame oil and light soy sauce, and topped with ginger and chilli.
Said Dr Leong, an infectious diseases specialist in private practice: "He fits nicely into the GBS cohorts that we have been seeing.
"There is a temporal relationship (between eating raw fish and being infected) of within a week, and the progress of the disease is rapid and at the typical sites."
GBS is a common bacterium found in the human gut and urinary tract of about 15 to 30 per cent of adults without causing disease, according to the Ministry of Health (MOH). (See report, right.)
It may, however, occasionally cause infection of the skin, joints, heart and brain.
Figures from MOH show that in the first half of the year alone, there have been 238 cases of GBS infections in public hospitals - a spike from the annual average of 150 cases in the past four years.
Mr Kuay was shocked to find out that the most likely cause of the infection was raw fish.
He recounted that his left knee started to swell on July 13.
Then, he thought he had merely pulled a muscle or a ligament as he had been cycling. A Chinese physician he saw on the same day told him the same thing.
But he started getting bouts of fever on top of the pain. "I have broken a bone before, and I can tell you - it hurt more than that," he said.
The first time he heard the words "Group B Streptococcus" was from his physiotherapist, whom he sought help from after the fever spells.
The physiotherapist referred him to an orthopaedic doctor as Mr Kuay's condition went beyond physical disability.
By then, Mr Kuay's left knee had swollen to twice its size due to the infection.
On July 15, he underwent the operation to drain out the pus in his swollen knee.
"I immediately texted my friends and said, 'If you've (read a report about GBS), please send it to me.' The reports already linked (GBS infections) to raw fish. Only then did I backtrack and realised I did eat raw fish.
He had to be hospitalised for a week before going to Dr Leong for his daily dose of antibiotics, administered intravenously.
At Dr Leong's encouragement to raise awareness of GBS infections, Mr Kuay shared what he went through on Facebook.
After connecting with both friends and strangers about GBS infections, he realised he was one of the luckier sufferers.
"Someone I know had multiple joint pains and was vomiting profusely. Another was infected in the brain and developed meningitis.
"An oncologist friend told me, 'Luckily you don't have to amputate.' He wasn't joking," Mr Kuay said.
Dr Leong also told him that one of his patients died within three days of being affected. (See report at far right.)
Mr Kuay said: "I felt grateful that my infection wasn't as bad. I also thought about those who did get it bad."
He added that the level of awareness of GBS infections should be raised so people can seek help fast if they suspect they are infected.
Though Mr Kuay is finally cleared of his GBS infection (as confirmed by a blood test on Wednesday), the recovery process is a long and arduous one. It will take another two months of physiotherapy sessions twice a week before Mr Kuay gains strength in his left knee again.