A norovirus outbreak at casual dining chain Wahaca has helped push the business into the red for the first time since parent company Oaxaca began filing full annual accounts in 2010.
Loss before tax was was £4.7m for the 52 weeks ended 25 June 2017, down 883% from a pre-tax profit of £640,000 the year before.
The company reported a modest increase in annual turnover of 0.4% to £46.6m (2016: £46.4m) for the same period.
The Mexican restaurant brand was forced to close nine of its London sites in October and November 2016 after an outbreak of norovirus that saw 200 staff and 160 diners fall ill.
In documents filed at Companies House Wahaca co-founder Mark Selby described the incident as a "one-off event" that resulted in exceptional costs of £700,000.
He said: "The results show the impact of a one-off event in October 2016 whereby an outbreak of Norovirus, widely reported in the media at the time, caused us to voluntarily close a number of our restaurants on a short-term basis, with a consequential loss in revenue and profit.
"Whilst this had a significant impact on our trading performance for the financial year, relative to the previous year the business has recovered from the event and continues to be in a strong position to grow, with ambitious future plans."