The Independent reports that Tesco, Waitrose and well-known health food shops have withdrawn tens of thousands of packets of edible seeds in one of the biggest product recalls in a decade after a survey found "unacceptable" levels of salmonella and E. coli.

One-in-50 packs of ready-to-eat seeds such as sesame and sunflower was found to be contaminated.

The study's authors pointed out that although there was no direct link to the contaminated seeds, 137 people in England and Wales fell ill from six sub-types of salmonella found in the seeds during the six-month study. Many more ill people are likely to have not reported their symptoms to GPs. The Health Protection Agency and the local authority group Lacors, which conducted the study, warned food manufacturers and retailers to improve hygiene during harvesting and drying of seeds.

The study was carried out because seeds – a popular snack among health-conscious shoppers wishing to avoid high-calorie chocolate and sweets – have become associated with at least seven outbreaks of salmonella in countries such as Germany, Norway, Sweden and Australia since 2000.

To gauge levels of contamination here, environmental health officers from 317 local authorities collected 3,735 packets of ready-to-eat seeds from 3,390 supermarkets, health food shops, convenience stores and market stalls between October 2007 and March 2008. They were analysed in 32 food laboratories.