An outbreak of Salmonella that has sickened more than 200 people is being investigated in England, France and Austria.
Public Health England (PHE) is investigating a national outbreak of Salmonella Enteritidis which has affected 156 people.
55 cases have been seen in Hampshire, 25 in London, 33 in Cheshire and Merseyside, and 43 in the West Midlands, said PHE.
French authorities are working on six outbreaks of S. Enteritidis affecting 49 people.
Isolates from cases and food samples largely conform to the outbreak strain but phage typing is not used in France so further work is checking to see if the outbreak involves the same strain as that in the UK cases.
The outbreak in Austria conforms to the outbreak strain but it is unclear how many people have been affected.
Chinese food link
The exact source is unknown but the increase in case numbers in June and July characterised by a series of local/regional outbreaks has been primarily linked to restaurants and takeaways serving Chinese food or similar cuisine.
Dr Paul Cleary, a consultant epidemiologist leading the PHE investigation, said it is working with the Food Standards Agency, local authorities and other public health organisations in Europe to investigate the cause.
“We are making good progress and hope to have more conclusive evidence shortly. We will continue to monitor the situation and if there is any further public health action necessary then we will ensure that this takes place.”
Reassessed as national outbreak
PHE said the English cases occurred as isolated clusters over several months and have been managed locally, but are being reassessed as potentially linked under a national investigation.
Testing has revealed that all of the cases are infected with closely related strains, indicating the cause of the illness is from a single source.
The multi locus variable number tandem repeat analysis (MLVA) profile of the food and environmental isolates from Cheshire and Merseyside is the outbreak strain.
Of the cases in Hampshire, 32 were connected with a single oriental restaurant.
In London, little is known of the food histories, 11 people have been hospitalised although it is unknown if Salmonella infection was the cause.
It has been found that 31 cases were connected with an outbreak at a single oriental takeaway in Cheshire and Merseyside.
In West Midlands 34 of illnesses were connected with the Birmingham Heartlands Hospital outbreak.
Whole genome sequencing shows some heterogeneity within the outbreak strain but indicates that all isolates are closely related and all those examined so far are sensitive to antimicrobials.
PHE said MLVA on further isolates is pending and investigations to establish links between cases are underway.
Professor Anthony Hilton, head of biological and biomedical science at Aston University, said if the cases are related the next stage will be identifying common risk factors associated with the infected individuals.
"This might be consumption of a contaminated food or ingredient or even a common exposure at an event or activity," he said.
“Compiling food and exposure histories of cases occurring over several months can be complex and time consuming depending on the quality of the information available and it may be some time before we know the true extend of the outbreak and the causative link, if any.”