There is no obvious source for a recent surge in coronavirus cases in Leicester, a report has found.
Public Health England (PHE) found “no explanatory outbreaks in care homes, hospital settings, or industrial processes”.
Its analysis of cases showed more “young and middle-aged people” in the city had tested positive for Covid-19 than in other parts of the Midlands.
But the spread did not appear to be “unconstrained”, it found.
The preliminary investigation said the increase in reported cases could partly be due to a “growth in availability of testing” in Leicester.
It confirmed a concentration of new cases in the North Evington ward of the city.
The report said hospitals in Leicester were currently treating 80 patients with Covid-19, 10 of whom required ventilation.
Patient numbers had “decreased rapidly” since a surge in early April but new admissions had “remained steady” at between six and 10 per day throughout June.
On Monday, as he announced a local lockdown for the city, Health Secretary Matt Hancock said it had “10% of all positive cases” over the previous week.