The Food and Environmental Hygiene Department (FEHD) and the Consumer Council conducted a joint study on histamine in canned fish and tuna sandwiches with an aim to assess the health risk of histamine in canned fish and tuna sandwiches. As improper handling and storage of canned fish after opening may result in high level of histamine, the study also explored the measures for reducing their formation.

2. Histamine is formed by conversion of the free amino acid histidine in muscle of dead fish with the presence of certain bacteria, mainly species of the family Enterobacteriaceae such as Morganella morganii. Consumption of fish containing high levels of histamine can cause foodborne intoxication, known as histamine poisoning (or scombroid fish poisoning). Histamine poisoning occurs throughout the world and is reported sporadically in Hong Kong.

3. In our study, the levels of histamine were measured in 23 canned fish samples (12 tuna, 5 sardines, 3 mackerels and 3 anchovies) and 20 tuna sandwiches samples which were sampled from different major retail outlets and restaurants in May 2005. To devise measures for reducing the formation of histamine, further experiment was performed in canned tuna samples which were kept under 3 different storage conditions (2oC, room temperature and 33oC respectively) with inoculation of the bacteria Morganella morganii. All the laboratory analyses were done by the Food Research Laboratory of FEHD.

4. Results showed that histamine levels in all the canned fish and tuna sandwiches samples were well below the maximum level in Codex standards. However, further experiment showed that high levels of histamine sufficient to cause histamine poisoning were detected in the tuna fish samples that were kept at room temperature for 24 hours, or at 33oC for 6 to 8 hours.

5. The public and the trade are therefore advised to observe personal and food hygiene to prevent cross contamination. Tuna sandwiches and opened canned fish should be stored at 4oC or below and be consumed as soon as possible. The trade is also advised not to store / display the tuna sandwiches at room temperature for more than 2 hours.

September 2005
Risk Assessment Section
Food and Environmental Hygiene Department

For the study report (only available in Chinese), please click the following website:
"Histamine in canned fish and tuna sandwiches (Chinese version)"