Recent accounts for the group's parent company Oaxaca show pre-tax losses of £4.7m for the 12 months to 25 June 2017, compared to a profit of £600,000 the previous year.
Turnover was £46.6m, a modest £200,000 increase year-on-year.
It comes after Wahaca was forced to close nine of its 25 restaurants in October 2016 after around 160 diners and 200 staff became unwell.
In Oaxaca’s financial statement director Mark Selby referred to the incident as a “one-off event” that had incurred exceptional costs of £700,000.
Selby wrote: “Whilst this had a significant impact on our trading performance for the financial year relative to the previous year the business has managed to recover from the aftermath of the event.”
Miers told BigHospitality last year that the “awful” incident had been a “line in the sand” and forced them to reconsider the future of the business.
The group has since launched its first Test Kitchen site in Shoreditch, where diners are asked to give feedback on trial dishes before they are rolled out across the main Wahaca menu.
The company's recent financial report states that though the UK economic climate remains uncertain Wahaca believes its menu offers “good value for money”, placing it in a strong position over its competitors.