(CNN) Customers at a restaurant and pub in Salisbury, southern England, were urged to wash their clothes Sunday after traces of the nerve agent used on a former Russian spy and his daughter were detected.

Customers who visited Italian restaurant Zizzi or The Mill pub from 1:30 p.m. March 4 to the evening of March 5 were advised to clean their clothes and any possessions they had with them at the time.

"We have now learned that there has been some trace contamination by the nerve agent in both The Mill pub and Zizzi restaurant in Salisbury," England's chief medical officer, Sally Davies, told reporters Sunday.

Davies said she was confident "this has not harmed the health of anyone" who was there. However, she advised people who visited the locations to wash their clothes and belongings as a precaution.

Sergei and Yulia Skripal.

Former Russian double agent Sergei Skripal, 66, and his daughter, Yulia, 33, remain hospitalized in "very serious condition" after being poisoned last week in Salisbury.

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