The recent spate of people becoming seriously ill from eating raw fish is only scratching the surface of the problem of eating raw freshwater fish ("Man, 52, critically ill after eating raw fish dish"; last Thursday, "Food stall operators taking raw fish dishes off the menu"; last Saturday, and "Eateries take steps to keep raw fish dishes safe"; Sunday).

Farmed freshwater fish inherently contains more bacteria and other harmful parasites than other types of fish, and should never be consumed raw.

Besides the Group B Streptococcus bacteria, freshwater fish may also be infected with the oriental liver fluke, roundworm and tapeworm.

Liver fluke, for example, can cause liver cirrhosis, chronic jaundice and cancer arising from bile duct cells, and these symptoms do not manifest until months or years later.

That is why the Hong Kong government has banned the consumption of raw freshwater fish for more than 30 years already.

And just this year, the United States health authorities started requiring all raw fish used in sushi, sashimi, tartare, ceviche and other similar dishes to be deep frozen before being served, to remove all bacteria and parasites.

Even sashimi-grade salmon is never served "fresh".

In Japan, all sushi chefs are trained to always freeze salmon at minus 20 deg C for at least 24 hours before serving.

Do we know if the salmon that yusheng restaurants serve is sashimi-grade or bought from the slabs sitting next to other fish in wet markets?

Also, local restaurants do not have the skill set or cold chain refrigeration equipment to ensure sashimi-grade raw fish food safety.

Lau Chee Kin