Leicestershire Health Authority Seventeen of the cases, mostly pupils, have been diagnosed since Monday.
Experts say the disease is now probably gaining a hold in the wider community.
People most at risk are those who have come into contact with the infected pupils. Another 60 students strongly suspected of having been infected have been given antibiotics as a precautionary measure. Maybe, and it is a maybe, if the vaccination scheme had continued, we wouldn't be seeing what we have today. But at the moment, the advice we are being given is that it isn't necessary. He said only one of the people affected had reached the infectious stage of the disease.