Twenty-three people, including 17 students, have tested positive to tuberculosis exposure at a Sydney school, the Department of Education says.

The staff and students from Hassall Grove Primary school in Sydney's west were in contact with a casual teacher working at the school.

"In October last year, the school was alerted that a casual teacher was assessed as having a full-blown case of tuberculosis," said Mark Davis, a spokesman for the Department of Education and Training.

"They contacted NSW Health, which put a management plan in place at the school in consulation with the school community, and informed parents, students and staff."

Public health officials from Sydney West Area Health Service (SWAHS) conducted a screening process for people who might have been in contact with the teacher, who is in her late 20s, SWAHS spokeswoman Vicki Sheppeard said.

Twenty-three people returned test results showing potential exposure and they received a complete assessment at the chest clinic, Dr Sheppeard said.

Mr Davis said last month the NSW Health Department tested a larger group of people at the school.

There were no positive results, and there was no ongoing risk of tuberculosis infection from the initial case, he said.

The teacher was from a country where tuberculosis was prevalent, Dr Sheppeard said.

She exhibited symptoms consistent with tuberculosis for only two weeks before she was diagnosed with the disease, she said.

She was hospitalised and treated successfully, and is no longer regarded as being infectious, Mr Davis said.

About 450 cases of tuberculosis are reported in NSW every year.

It is a disease caused by infection with the bacteria mycobacterium and can damage a person's lungs or other parts of the body and cause serious illness. It can be treated with antibiotics.