One-third of sushi delivered by takeaway sushi services contains excessively high levels of bacteria, according to a survey by the consumers’ association Consumentenbond.

Tests carried out at 20 takeaway locations around the country found that nine failed to meet hygiene standards. Most sushi was contaminated as a result of being handled with dirty fingers.

Traces of e.coli bacteria, which can cause diarrhoea and vomiting, were found at two restaurants in Groningen and Amersfoort, while two dishes at Sushi Time in Leiden contained bacillus cereus, which can cause food poisoning.

Four restaurant chains – Sushipoint, Sumo Sushi Express, Shabu To Go and Sushi Time – were included in the survey, along with individual restaurants in Breda, Leiden, Amersfoort, Rotterdam and Groningen. Most of the sushi tested was fresh and hygienically prepared, inspectors said.

The best rated restaurant was Sushipoint in Leiden, with an overall score of 9.6 out of 10, followed by Mr Sushi and Miss Wok in Breda on 9.1. Sushipoint also came out as best of the chains with an average score of 8.6.