Mexican restaurant chain Wahaca has shut nine of its restaurants after a suspected outbreak of norovirus.Public Health England (PHE) said it had launched an investigation after 205 staff and 160 members of the public fell ill.Wahaca, founded by 2005 MasterChef winner Thomasina Miers, said it voluntarily closed the doors to nine sites.A spokeswoman told the Daily Mirror: “We can confirm a number of our employees and customers have reported becoming ill over the past week. “Initial tests suggest that the cause of this illness was norovirus. Following these reports, Wahaca voluntarily closed nine sites.”Deborah Turbitt, London deputy director for health protection for PHE, said the source of the outbreak was yet to be determined.She said: “Public Health England has been notified of a suspected norovirus outbreak at a restaurant chain.”We are working closely with environmental health officers and the restaurant chain to investigate.”We have so far been made aware of 205 staff and 160 members of the public reporting illness, however these are unconfirmed cases.”Currently, the source of the outbreak is not confirmed and this remains under investigation.” Specialists cleaned all Wahaca restaurants and later reopened five affected sites, the chain’s spokeswoman added.Its website showed the closed restaurants include Canary Wharf, Covent Garden, Oxford Circus, Soho and White City, all in London.The virus causes diarrhoea and vomiting and those afflicted generally return to full health after a few days.But the NHS advises calling a GP or the 111 helpline if symptoms persist. A branch of Wahaca (library picture) Thomasina Miers at home, London Credit:Martin Pope Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.