Eight in ten Thais in a new survey knew raw freshwater fish can make you ill. Seven in ten had eaten it anyway, and in Vietnam the people who knew the risk ate it more

Along the Mekong, some of the best-loved dishes are made from river fish that is never cooked. Koi pla in Thailand and its Lao twin koi pa are minced raw fish salads sharpened with lime and herbs. Pa-daek in Laos, pla-ra in Thailand and prahok in Cambodia are fish fermented with salt, eaten as a paste or a sauce. They are old and they taste of home. They can also carry liver flukes, small parasitic worms linked to disease of the liver and bile ducts, and bacteria that can cause invasive infections. A team led from the National University of Singapore wanted to know how many people still eat these dishes and whether knowing the danger changes anything. Their paper came out in BMJ Public Health on 5 October 2026.

Between October 2022 and February 2024 they surveyed 6,021 adults aged 21 and over in Cambodia, Laos, Malaysia, Singapore, Thailand and Vietnam, about a thousand in each. Everyone was shown four to six local dishes and asked how often they ate each one. The researchers sorted the dishes into high risk (no heat at all in the preparation) and low risk (some heat, but possibly not enough). People were also asked where they ate the dishes, where the fish came from, and whether they knew that eating raw fish can make you ill.

The eating first. In Vietnam 98.7% said they had eaten at least one high-risk dish, in Laos 96.9%, in Cambodia 95.5%, in Malaysia 83.7% and in Thailand 72.4%. Singapore, which banned raw freshwater fish in ready-to-eat dishes after an outbreak in 2015, was far lower at 31.9%. For many people this is everyday food, not a festival dish: half the Lao participants (50.7%) said they ate pa-daek at least once a week, and about one in five Cambodians ate each of four uncooked dishes that often.

Now the knowing. In Thailand 79.2% agreed that raw fish can cause sickness, in Vietnam 77.5%, in Singapore 74.2%, in Laos 71.1%, in Cambodia 59.7% and in Malaysia 43.0%. Put the two lists side by side and they barely relate. Thailand has run national campaigns against koi pla for decades, and the paper credits them with cutting liver fluke infection from over 15% of people in 1996 to 2.2% in 2019. Yet about 40% of the Thai participants still said they eat koi pla, and about 90% of the Lao participants eat koi pa although seven in ten of them knew the risk.

Two results went against what you would expect. Only in Singapore did not knowing go with more eating: people unaware of the risk were about 1.6 times as likely to eat a high-risk dish. In Vietnam it ran the other way, and strongly. People who did not know the risk were far less likely to eat these dishes (adjusted odds ratio 0.18), which means those who knew were the ones eating them. And in four countries, people aged 40 and over were less likely to eat high-risk dishes than younger adults. The authors had expected tradition to sit with the old, and say so.

Why would people who know keep eating? The authors lean on earlier research from Thailand and Laos: these dishes are part of who people are, elders have objected that giving up koi pla goes against tradition, and some men tie raw fish to strength and virility. In this survey men were about twice as likely as women to eat high-risk dishes in Vietnam and Laos. Most of the eating happens at home (between 47% and 89% of participants, depending on the country), where no inspector goes, and a quarter of Lao participants and a sixth of Cambodians caught some of the fish themselves.

The cautions matter here, and the authors raise the main one. This was an online survey, through a market research panel in five countries and social media adverts in Singapore, so it leans young, urban and educated even after weighting. The rural Mekong communities where flukes are most common were under-represented. Nobody was tested for infection, so the study says nothing about who actually got ill. 'Ever eaten' includes people who have the dish once or twice a year. Some of the odds ratios rest on small groups: the finding that university-educated Lao participants were seven times as likely to eat high-risk dishes has a confidence interval running from 2.3 to 29.

Two things we noticed ourselves. The paper's summary says between 70% and 90% had eaten high-risk dishes in the four Mekong countries, while its own results give over 95% for three of them. And the high-risk list is broader than 'raw river fish' suggests: Malaysia's includes budu, which the paper's table describes as fermented anchovies, and anchovies are sea fish. Counting long-fermented pastes and dried fish alongside freshly minced raw fish may be the cautious choice, but it lifts the totals. Our reading: the headline percentages are soft, and the gap between knowing and doing is the solid finding. For anyone eating or travelling in the region, the paper's practical point is simple. Heat is what makes freshwater fish safe. Lime juice, salt, pickling and fermenting are not cooking, and freezing at −20°C or below for one to seven days kills the flukes but not the bacteria.