Public Health England has begun an investigation after 300 people, including 205 staff and 160 customers, fell ill.
Of the nine restaurants originally closed, four have reopened and the remaining five are expected to reopen soon, on a case by case basis. The affected restaurants, all, cited in London include Covent Garden, Canary Wharf, Oxford Circus, Soho and White City.
In a statement, Wahaca co-founders Mark Selby and Thomasina Miers, said: “Last week a number of our staff and customers were struck down by what is suspected to be the winter vomiting bug, norovirus.
“We assessed each case and when it became clear they were not isolated incidents, we got in touch with relevant officials at Public Health England and Environmental Health Officers. In tandem with that, we took our own precautionary measures – voluntarily closing affected restaurants, carrying out anti-viral deep cleaning at all of our restaurants, whether affected or not, and ensuring that any staff member who had reported illness remained off site until their symptoms had ceased for at least 48 hours.
“Our amazing teams have worked tirelessly to ensure that we have done everything within our power to limit any risk to our customers and team members, and the situation remains under control and we continue to work with all local authorities to monitor this closely.
“The majority of our restaurants are open and we hope to reopen the 5 remaining sites, on a case by case basis, as soon as we feel we are ready to do so.
“We are incredibly sorry that people have been unwell. In the 9 years since we first opened Wahaca we have never had such an unprecedented incident, and we are doing everything we can to get to the bottom of how this may have happened.”
Deborah Turbitt, London deputy director for health protection for PHE, added: “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.”