Doctors and school authorities have moved to reassure parents at Bishopsford school, after alerts about two serious illnesses were sent to parents in the space of 24 hours.

Last Monday letters were sent to parents warning that a child at the Morden school had developed tuberculosis (TB), and the following day it was announced that a pupil’s sibling had contracted swine flu.

This week health authorities said because the risk to other pupils was low, the school should remain open - but asked families to be vigilant for symptoms, particularly of the more serious TB.

Dr Anita Roche, a consultant at the South West London Health Protection Unit, said: “Tuberculosis is a disease that typically requires close, lengthy and frequent contact before transmission occurs. Because of this, the greatest risk of spread is to people who live in the same household as a person with this disease. The risk to other contacts, including those in a school setting, is low.”

The school letter said special screening had been arranged for those who had “close and prolonged contact” with the TB sufferer.

The swine flu alert came after a girl at Bishopsford was found to have a sibling with the illness at Cranmer Primary School.

Yvette Stanley, Merton Council’s director for children, schools and families, said the school was following the Health Protection Agency’s (HPA) advice that “business should continue as usual”.

She said: “During this time it is important that children's education is not affected and we will continue to work closely with the school and the HPA to ensure that pupils, parents and staff know where to go if they need further information or advice."

Parents should NHS Direct on 0845 4647 or the South West London Health Protection Unit on 020 8812 7850 for more advice.