Advisor at Japan Food Research Laboratories
In my column #13, I have presented the preliminary figures of Japanese food-poisoning occurrence in fiscal 2014 released by Ministry of Health, Labour and Welfare. Out of total 977, 441 food poisoning cases were caused by bacteria. Number of their sufferers was 7,213. It is followed by food poisoning caused by viruses whose sufferers rose to 10,693. The Ministry subsequently provided the definite numerical value of domestic food-poisoning occurrence in that year. This turned out to be not so different from the preliminary figures. I have provided the breakdown for the bacterial food poisoning cases in Table1.
Note: Serious listeria food poisoning incidents have been reported mostly from developed countries and recalls associated with this bacterium have been launched. Japan should take countermeasures against this bacterium.
1) Unexplained food poisoning until 1950
This piece of column will deal with vibrio parahaemolyticus food poisoning. This halophilic marine bacterium was first discovered as a causative microorganism of dried whitebait food poisoning by Professor Tsunezaburo Fujino of Osaka University in 1950. Most of the unexplained seafood poisoning until that time are thought to have been caused by vibrio parahaemolyticus.
Along with the resent spread of ichthyophagy, number of food poisoning incidents caused by this bacterium is increasing across the globe. In spite of this trend, the number in Japan is decreasing owing to the coherent efforts from fishing grounds to dinner tables. Although seafood consumption in Japan keeps the same level, only 6 food poisoning incidents and 47 sufferers caused by vibrio parahaemolyticus have been reported in 2014 as shown in Table1. From 1960s to around 2000, the number of vibrio parahaemolyticus food poisoning cases had been 300 to 500 and their sufferers 8000 to 15,000, but the figures started to decrease around 2000. This confirms that Japanese countermeasures against vibrio parahaemolyticus food poisoning have achieved the desired results.
Vibrio parahaemolyticus lives in the sea or bottom sediment. As shown in Figure1, this microorganism requires saline concentration of 2 to 7% in food to multiply. It has a low tolerance for freshwater, application of heat, and drying. There are two types of Vibrio parahaemolyticus; one causes food poisoning and the other is non-pathogenic. Pathogenic Vibrio parahaemolyticus is regarded to produce both thermostable direct hemolysin (TDH) and TDH related hemolysin (TRH) or either one of them. Most of the Vibrio-parahaemolyticus food contamination is caused by non-pathogenic ones and pathogenic vibrio parahaemolyticus rarely contaminate food. Its bacterial content to develop a disease is estimated to be 1000 to 100000 or more and food poisoning will not occur without proliferation of pathogenic vibrio parahaemolyticus. Therefore, it is necessary to prevent pathogenic vibrio parahaemolyticus from proliferating in food (marine products).
In 2001, a law for reducing vibrio parahaemolyticus food poisoning was revised as shown in Table2. It stipulates that caught fish/shellfish should be kept at low temperature by such means as ice in order to prevent vibrio parahaemolyticus proliferation. It also specifies that washing water at fish markets should be vibrio-parahaemolyticus-negative tap water or sterile seawater, and brackish river water or seawater which is possibly contaminated should not be used. Moreover, vibrio parahaemolyticus count should be less than 100 per gram for fish/shellfish to be eaten raw, and boiled octopus or crab should be vibrio parahaemolyticus negative. As for distribution, fish/shellfish should be preserved at lower than 10°C aiming at prevention of vibrio parahaemolyticus proliferation.
Although it is desirable to keep temperatures below 8°C to prevent vibrio parahaemolyticus food poisoning, the standard specifies as below 10°C due to the feasibility in Japan. I think food should be refrigerated below 4°C considering the possibility of proliferation of food poisoning bacteria such as Listeria or Yersinia. WHO(World Health Organization) advises that food should not be kept at the temperature from 5 to 60°C, which is a hazardous temperature zone for preservation and distribution of food.
Number of vibrio parahaemolyticus food poisoning in Japan has been decreased not because number of food/shellfish contaminated by vibrio parahaemolyticus has been reduced. This decrease owes to legislative preparations aiming at controlling risk based on scientific grounds and to improvement efforts at each process of seafood chain from production to consumption. Marine surveys have been revealing the existence of O3:K6 vibrio parahaemolyticus food-poisoning pandemic strain and other serotypes of pathogenic vibrio parahaemolyticus. These food-poisoning bacteria have been detected from Japanese marine products too. I believe we should keep up the countermeasures against vibrio parahaemolyticus food poisoning and stay on our guard.
1) Homepage of the Food Safety Commission of Japan: Risk Profile for Health Effects Assessment of Food --- Vibrio Parahaemolyticus in Fresh Fish and Shellfish (revised version, 2012)
2) KUDO, Y., “Rapid Decrease of Vibrio Parahaemolyticus Food Poisoning in Japan and Verification of the Effects of Countermeasures“, Japanese Journal of Food Microbiology, 30(4), 177-185(2013).