When a common bacteria made more than 350 people ill last year - some of them seriously - doctors were mystified.
One man slipped into a 10-day coma when the bacteria attacked his brain; another had his hands and feet amputated. Two people died.
But researchers are now a step closer to understanding the Group B Streptococcus (GBS) bacteria, which was behind a spate of infections which occurred after people ate Chinese-style raw fish dishes.
After looking at the MRI scans of 14 people who came down with GBS infections last year, Professor Tchoyoson Lim noticed something unusual.
"(The scans) showed us that there was a lot of pus in the space between the brain and the bone, much more than what we expect to see in other types of brain infections," said Prof Lim, a senior consultant at the National Neuroscience Institute's (NNI) neuroradiology department.
"We don't really know why - it could be that this strain is more virulent than other types and produces more pus."
In addition, the scans revealed tiny abnormalites in the brain itself. This could be pus, said Prof Lim, or the result of tiny strokes in the brain.
In babies, he explained, GBS infections are known to obstruct blood vessels and cause strokes. Something similar could have happened in the adult patients.
What this means, said his colleague, Associate Professor Kevin Tan, is that doctors should keep an eye out for such unique symptoms.
Said the senior consultant in NNI's neurology department: "If people see these kinds of patterns (in an MRI), they need to consider a GBS infection."
Both professors are part of a group called the Singapore Neurologic Infections Programme, which studies infections of the central nervous system.
In June last year, the group noticed something odd: They were getting four or five patients with brain infections in a fortnight, instead of the usual one a week. It was their first inkling that an outbreak was going on.
While GBS is a common bacteria often found in the gut without causing disease, the culprit behind last year's infections was a strain of the bacteria called Sequence Type 283 - believed to be more aggressive.
The bacteria was traced to yusheng, or Chinese-style dishes using freshwater raw fish. Hawkers were banned from selling these dishes, and the infections stopped.
"We don't yet know the source and origin of this outbreak. Was it due to a batch of bad fish, for example?" Prof Lim said. "But we do know that over the years, some patients who have never eaten raw fish have had this. We are working to establish whether this strain has been hiding in the background."
But that is just the tip of the iceberg. Apart from following up on the original 14 patients, doctors also plan to review more GBS cases. This will tie in with efforts by a national work group set up to study the virus and its effects on other parts of the body, such as the joints.
"We want to compare GBS with other types of brain infections and see how they are similar or dissimilar," Prof Tan said. "It's one step in the direction of understanding a bit more."