SINGAPORE - Fish in Singapore is still safe for consumption, although it is likely that the Jurong Fishery Port cluster cases came from Indonesian or other fishing boats and via multiple points, said Singapore's director of medical services Kenneth Mak on Tuesday (July 20).
"We have no evidence to suggest that transmission is occurring through contaminated fish. We believe that the fish that we still consume and enjoy remain safe for consumption," he said at a press conference held by the multi-ministry task force tackling Covid-19.
There were 321 cases linked to the Jurong Fishery Port cluster as at Tuesday.
"This number will rise as we find more cases at these places and in the other wet markets," said Associate Professor Mak.
Infections have been detected at a total of 28 markets and food centres, Health Minister Ong Ye Kung said at the press conference on Tuesday.
Prof Mak added that tests of the first group of cases have identified the Delta variant to be the cause of Covid-19 infections in this cluster.
"The identified variant of concern has features that are similar to what we've seen in other cases that we have picked up in imported cases from Indonesia," he said.
"So we believe that Covid-19 infection in this cluster has been introduced, perhaps via sea route, into the fishery port, likely from Indonesian or other fishing boats that have brought fish into the port. The exact mechanism of transmission from the boat to people who operate stalls in the port isn't entirely clear."
While there have been efforts to make the operations at the fishery port as contactless as possible, it is very challenging to maintain safe management measures there due to the hot and humid environment and nature of activities there, said Prof Mak.
These include strenuous activities like carrying heavy barrels of fish and ice, and some mask-off activities and close interactions likely would have taken place between the people there, he added.
"Fomite transmission on contaminated surfaces and at the stalls remains a strong possibility for transmission," said Prof Mak, noting that the index case of Covid-19 transmission occurred in a wet market in Wuhan, China, and other outbreaks have also happened at similar markets in places like Thailand, Sri Lanka and Europe.
Fomite transmission refers to spread that occurs through a contaminated article or surface.
Prof Mak said: "This is an area where we will continue to work closely with our partner sector leads to review the safe management protocols in place and review the need for routine regular testing to detect infections early in these settings and to disrupt potential chains of transmission.
He added that tests also suggest the clusters linked to the fishery port and wet market may not have been due to a single point of introduction of infection.
"Exposure may have occurred over a period of time, with multiple points of injection of infection because the genetic information for variants that we've identified so far are not completely identical across the different cases."
"So we are not able to determine how long these episodes of introduction have occurred over or who might have been a specific super spreader leading to the cluster that has emerged."
At least one Covid-19 patient who worked at the Jurong Fishery Port frequented a KTV lounge within the infectious period, he said.
"It is, however, not possible for us to verify whether that individual did transmit an infection because the diagnostic PCR (polymerase chain reaction) test performed on that individual detected the presence of Covid-19 virus, but it was at a very low count," said Prof Mak, adding that at such very low viral loads, there is not enough of the virus to carry out the tests.
He added: "From the public health perspective, it is less important for us to confirm that link between the fishery port and the KTV lounge. Irrespective of how transmission has taken place, there are cases and growing clusters in each setting.
"The numbers of cases that we're picking up from the wet market testing continues to grow, and this remains a cause for concern."
How the virus could have spread at Jurong Fishery Port
Singapore’s director of medical services Kenneth Mak said that tests of the first group of cases linked to Jurong Fishery Port have identified the Delta variant as the cause of Covid-19 infections in this cluster, with similar features to those seen in imported cases from Indonesia.
1. Infections introduced
• Infections in the Jurong Fishery Port cluster were likely introduced via the sea from Indonesian or other fishing boats that brought fish into the port, said Associate Professor Mak. The exact mechanism of transmission is unclear.
• Exposure may have occurred over a period of time, with multiple points where infection was introduced.
2. Spread in the cluster
• The virus could have been spread through contaminated surfaces and at the stalls, added Prof Mak.
• The hot and humid environment, with workers engaged in strenuous activities like carrying fish and ice, also means that some mask-off activities and close interactions between people likely would have taken place
3. KTV lounge
At least one Covid-19 patient who worked at the Jurong Fishery Port frequented a KTV lounge within the infectious period.