European health officials investigating the salmonella outbreak linked to Kinder chocolate products have said they suspect it is related to buttermilk used in a Belgian factory.

A “Rapid Outbreak Assessment” released by the European Food Safety Authority and the European Centre for Disease Prevention and Control said they had matched the same salmonella strain currently infecting people to samples taken from a factory in Belgium last December.

The report said “the processing step involving buttermilk was identified as the possible contamination point”, and hygiene measures were implemented.

The report said the factory “distributed the implicated chocolate products across Europe and globally after negative Salmonella testing”.

Authorities have previously named the company involved as the Italian chocolate firm Ferrero.

On April 8, the food safety authority in Belgium assessed that the factory was not able to guarantee the safety of its products, and as a result “the authorisation for production was withdrawn”.

The report said: “This outbreak is rapidly evolving, and children have so far been most at risk for severe infection among reported cases.

“The recalls and withdrawals launched worldwide will reduce the risk of further infections.

“However, further investigations are needed at the production site to identify the root cause, timing, and possible factors behind the contamination, including the evaluation of the possibility of the wider use of contaminated raw material in other processing plants.”

A UK recall of Kinder chocolate products was extended on Friday to include all of those manufactured at the Belgium site since June, regardless of their best-before date.

The previous recall only covered products with best-before dates up to October 7 2022.

The recall was related to the same products – Kinder Surprise, Kinder Mini Eggs, Kinder Surprise 100g and Kinder Schokobons – announced earlier in the week.

Ferrero also said it was suspending operations at its plant in Arlon, which it said will only reopen “once certified by the authorities”.

The firm said it acknowledged “internal inefficiencies, creating delays in retrieving and sharing information in a timely manner” and said these had “impacted the speed and effectiveness of the investigations”.

The UK Health Security Agency (UKHSA) said on Friday that 67 people in the UK are known to have been infected with salmonella in the outbreak linked to the treats.

The majority affected are under five years old, the agency added.

The UKHSA has said the symptoms of salmonellosis usually resolve themselves within a few days but that symptoms can be more severe, especially in young children and those with weakened immune systems.

Symptoms of salmonella include diarrhoea, stomach cramps, nausea, vomiting and fever.

Anyone with concerns that they might have salmonellosis is urged to contact their GP or call NHS 111.