Five more Freyberg High School students have been confirmed as testing positive for pulmonary tuberculosis.

And some people  considered at risk have yet to have the blood test that could rule out the disease.

Last month a 15-year-old boy from the Palmerston North school was confirmed as being in isolation with TB and has since been confirmed as having the multi-drug-resistant form of the disease.

Almost 200 students who had been in classes with the teenager underwent blood tests  this month and the MidCentral public health service said it had yet to get in touch with those people who failed to show for the test to arrange for a blood sample to be taken.

MidCentral medical officer of health, Dr Rob Weir, said the  service had been working closely with the school, and information had been provided to parents, caregivers and teachers.

However, one parent, who did not wish to be named, was critical about the lack of information given to the students.

"My daughter was tested and I think it would have been nice if those students had been sat down and told what the facts were and how contagious it was. 

"She was really scared because she knew nothing and she hates needles. But she fronted up and did it.''

A letter was sent to all parents by email when the disease was first diagnosed. They  have since been sent a follow-up letter outlining  developments.

Dr Weir said the students had tested positive for latent tuberculosis, which was when the  germs were dormant. He said it was not possible to tell if a person who was positive for latent tuberculosis acquired it recently or in the past.

"Only 5 to 10 per cent of people with LTBI [latent tuberculosis infection] go on to develop active TB disease at some stage in their lives.''

Dr Weir said  people can carry the disease all their lives and not show symptoms.

The multi-drug resistant form that the initial patient has is more difficult to treat than normal tuberculosis as it is resistant to the two first-line  medicines, and treatment takes longer compared with the drug-susceptible form.

"I do want to reassure students, caregivers and teachers that TB is a disease which is hard to catch, develops slowly and can be cured.  

"We have all the systems and resources in place to cope with this situation,''  Dr Weir said.

Those who had returned a positive result had been offered chest X-rays.

"These people have also been offered close follow-up for two years, including ongoing chest X-ray monitoring,'' he said.

- © Fairfax NZ News