Salmonella that originated in Wales has now spread to English sickening at least 50 people with ham from independent butchers as the suspected source.
Wales has 21 confirmed cases and there are 30 in England, with nine known to have required hospitalisation.
Consumption of cooked ham from small independent butchers has been identified as a potential common link to the illness but so far names of the establishments have not been released.
Testing has been carried out on ham supplied to a number of butchers identified in the investigation.
Salmonella testing continues
No trace of Salmonella has been found, but other hygiene issues were identified that led to one supplier voluntarily withdrawing certain batches of ham.
FoodQualityNews.com reported on the outbreak when it began with cases recorded since 20 July.
The outbreak of Salmonella Typhimurium, across England and Wales is being investigated by Public Health England, Public Health Wales, the FSA and local authority environmental health officers.
It was first detected in Wales and centred mainly in North Wales (Conwy and Gwynedd), with additional clusters being investigated in England in the Thames Valley, Leeds, Cumbria and Stafford.
Cases are widely geographically distributed in patients aged seven months to 87 years, said the UK Food Standards Agency (FSA).
Rates of salmonella in Wales and the UK have fallen in recent years from a peak of infection recorded in 1997.
In Wales during 2011, the reported rate of salmonella infection in the general population was 15 cases per 100,000 people.
This compares to a rate of 15.5 the year before and 80 cases per 100,000 in 1997.
Salmonella Typhimurium cases totalled 1,959 in 2010 which was a drop from 1,920 the previous year, according to the Health Protection Agency Centre for Infections.