High counts of E.coli in shellfish beds has contributed to a consistent increase in microbiological contamination incidents, the Food Standards Agency (FSA) has reported.
Incidents of microbiological contamination have increased from 147 in 2006 to 390 last year, according to the FSA's Annual Report of Incidents.
It is the only category where incidents have been consistently increasing over time.
Last year, almost a third (32%) of reported microbiological incidents resulted from shellfish bed monitoring.
The FSA said high counts of E.coli were an indicator of poor hygiene in harvesting areas.
It said the reason for the large increase last year was unclear, but it was thought to be due to environmental factors such as higher rainfall causing an increase in run-off from fields.
Overall, the FSA investigated 1,645 food, feed and environmental contamination incidents in the UK last year – a similar figure to recent years.
About 61% of incidents originated within the UK, 9% related to food from the rest of the EU, and 21% were due to imported foods from outside.
The origin of the remaining 9% could not be identified.
Microbiological contamination made up 24% of incidents, followed by problems with veterinary medicines (13%), environmental contamination (12%) and natural chemical contamination (9%).
The number of veterinary medicine incidents last year was about five times the average in the years 2006 to 2012 but this reflected a change in reporting procedures, the FSA said.
Fires were the cause of almost four out of every five environmental incidents (79%) and almost all the others were the result of spills and leaks or contamination by heavy metals.
An FSA spokesman said: "The high proportion of microbiological contamination incidents linked to shellfish beds partly reflects the amount of statutory monitoring required in this area."