The HPA's most recent study identified pregnant women from ethnic backgrounds and those living in deprived areas as being at higher risk.
People in less wealthy areas tend to use smaller local retail outlets, which have been linked to a lower microbiological standard of food, said Dr Iain Gillespie, head of listeria surveillance at the HPA.
Local Government Regulation (formerly Lacors) and the HPA last month embarked on a joint six-month study to assess the microbiological safety of high-risk foods associated with Listeria monocytogenes (Lm) in small retail outlets.
The incidence of listeriosis the foodborne illness associated with the bacteria Lm has doubled in England and Wales since 2001. It mainly affects the elderly and those with weakened immune systems, but can also pose a significant risk to pregnant women, their unborn babies and newborns.
l Food Manufacture is holding a conference 'Emerging food safety issues' in October. Details at: www.foodmansafety.co.uk.