Pupils at a Peterborough school are to be tested for tuberculosis after a teaching assistant was diagnosed with the airborne disease.
TB kills at least 2m people a year
Parents of the 1,250 children at Orton Longueville School in Cambs received letters on Friday to reassure them.
It says that despite some pupils having been in close contact with the victim, the disease is "not easy to catch."
The Health Protection Agency will treat anyone who has been in close contact with the staff member.
Fatal if untreated
It is believed that between 25 and 35 pupils, who have had one-to-one contact with the staff member during the contagious stage of the disease, will be tested first.
If they should prove to have picked up the symptoms and are infected, then tests will be extended to other children and staff.
The disease, which usually attacks the lungs, can be fatal if left untreated.
Dr Kate King, from the Cambridgeshire and Peterborough team of the Health Protection Agency, said: "The important thing is that there is no need for an urgent reaction. There is no cause for alarm and nothing anyone need do at this stage."
It is thought the TB victim lived abroad as a child and picked up the disease there, although it has not shown itself until now, having been latent in their system.