Professor Dominic Harrison, Blackburn with Darwen Council's director of public health, warned last week the area had two weeks to get the numbers down before lockdown measures are reversed.
The Lancashire town brought in extra restrictions last Tuesday and said the borough of 148,000 people was facing a "rising tide" of cases.
He said data showed household "clusters" of infections, suggesting one person was infecting others in the same household and this was mainly affecting the south Asian population.