Nine London branches of the Wahaca Mexican streetfood chain were closed after a norovirus outbreak infected 360 customers and staff last week.

Four have reopened, but five branches remain closed: Covent Garden, Oxford Circus, Soho, Charlotte Street and Kentish Town.

The three-night Day of the Dead fiesta scheduled for the Vaults at Waterloo on Thursday, Friday and Saturday November 3-5 has also been cancelled. Ticket-holders will be reimbursed automatically next week.

Co-founders Thomasina Miers and Mark Selby said they had now carried out anti-viral deep cleaning at all their restaurants, whether involved in the outbreak or not.

“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 Offices.”

Norovirus causes severe vomiting and diarrhoea, and is spread by close contact with an infected person, including via food. It is unusual for an outbreak to occur simultaneously in several venues.

Miers opened the first Wahaca in 2007, and now has 17 branches in London and another eight around Britain. The Harden’s Survey has praised the chain for its “fun, fresh Mexican street food” served by “obliging” staff.