This precaution was taken after a member of the staff of the Bedok North school was found to have contracted an active form of the TB bacteria.
The New Paper understands that it was a teacher, but it is not known what subject he or she teaches. The school vice-principal, Mrs Angelina Tan, said in an e-mail in response to queries by TNP that a staff member was diagnosed with TB and is on medical leave.
She added that the person is recovering well and that this was the first case of TB in the school. The e-mail did not address our query on how long the person had symptoms of TB before being diagnosed and whether the person was hospitalised.
Mrs Tan said that the "safety and well-being of the children is of utmost importance to the school".
She added: "We have been working closely with the relevant authorities to identify and screen the (employees) and pupils from two Pri 6 classes who were in close and prolonged contact with the staff member.
"We have also met with the parents of these pupils to explain the nature of TB infection and screening as well as to assure them of the school's support.
"The teachers and school counsellors have provided counselling to the pupils and will continue to monitor the well-being of the pupils."
She added that all its staff and pupils from the two classes are currently well and the pupils are focused on completing their PSLE, which ends next Wednesday.
A spokesman for the Ministry of Education (MOE) said it was informed by the school after the relevant authorities had confirmed the TB case.
Responding to queries by TNP, she said in an e-mail: "The school has been working closely with the authorities to render support to the staff members and pupils who had prolonged and close contact with the affected personnel.
"Parents of the affected students have been informed, and the school has worked closely with the authorities to ensure that the screening tests were conducted at an appropriate timing to minimise inconvenience to students."
Associate Professor Sonny Wang, a senior consultant and director of Tan Tock Seng Hospital's Tuberculosis Control Unit (TBCU), described the protocol to befollowed if a student or teacher tests positive for active TB.
He said: "Students who have been identified by the TBCU as close contacts will be screened for symptoms. A skin test will be done and a chest X-ray performed, if necessary."
"The skin test involves injecting a minute amount of test material into the skin and the skin reaction is measured by the nurses 48 to 72 hours later.
"In some contacts, the skin test will be repeated two months after the last contact with the TB case. All in all, two to four visits to the TBCU for testing is required."
A parent of one Pri 6 pupil who was tested said MOE and the Ministry of Health should investigate the matter further.
"I got a letter from the school two weeks ago through my daughter telling me about the screening. Although my daughter tested negative for TB, every parent will naturally worry," he said.
The man, who gave his name as Jack and would only say that he works in construction, said his daughter is now sitting for the PSLE, but he questioned whether it was enough to test only two classes.
"The teacher could walk around and whoever is suay (unlucky in Hokkien) could get it, right?" he said.
Dr Ong Kian Chung, a respiratory specialist of almost 20 years, said it is important to prioritise and test only those who are high-risk contacts.
"Otherwise, you are challenging your immune system unnecessarily and your body may have a stronger reaction to future TB skin tests.
"You may test positive in that case, not because you have actually picked up TB, but because you had an earlier test. This is called a false positive result.
"So it's best not to complicate matters by testing indiscriminately," he said.
As it is, it's easy to get a false positive result because a skin reaction can also arise when the injected area is touched, causing swelling and itching.
Any positive result from the skin test has to be followed up with an interview to see if TB symptoms are present (see report above) and the person will also need a chest X-ray.
If the person shows no symptoms, he is considered to have latent TB and will be prescribed a nine-month course of medication.
It takes 2 to 3 days to confirm TB test results
The result of the Mantoux skin test for TB exposure takes between 48 and 72 hours to confirm.
The tests are mainly to detect latent TB infection, for which preventive treatment, in the form of drugs such as isoniazid, can be given to prevent the subsequent development of TB.
People with latent TB infection have TB germs in their bodies but they are not sick because the germs are not active.
They do not have symptoms of TB, such as a prolonged cough for more than three weeks, sputum production, coughing up blood, fever, night sweat and weight loss.
Those with latent TB infection cannot spread the germs to others.
Although the TB germs are inactive, they are alive. Later, perhaps many years later, they can become active, multiply and damage the lungs or other body organs.
A healthy person who is recently infected has a 10 per cent chance of developing TB in his lifetime. The risk is highest in the first two years following infection.
So recently infected people are advised to have preventive treatment to kill the TB germs before they become active.
Associate Professor Sonny Wang of the Tuberculosis Control Unit said: "TB drugs curtail the spread of TB very effectively if the TB patient takes the medicines regularly.
"The best quarantine is the 'chemical quarantine', where the patient undergoes treatment under TBCU's DOT (Directly Observed Treatment) programme.
"This way, as long as the patient is taking the medicine religiously, he or she is safe to others.
As such, no physical quarantine measures are necessary. Instead, the infectious case must adhere to treatment until it is completed to ensure he or she remains non-infectious to others."
Most infections happen because of prolonged close contact. One example is living in the same household for weeks or months with the person with TB, which causes them to "share the air", he added.
Bedok school had active case in April
In April, The New Paper reported about a 17-year-old female student in Bedok Town Secondary School who had an active tuberculosis infection.
As a result, about 45 students were screened for TB. About 10 subject teachers also voluntarily went for screening.
Its principal, Mr Chia Chor Yann, told The New Paper yesterday that there has been one more active infection in a student since then, but he is not "unduly alarmed".
"On the whole, in Singapore, TB is not that rare, so there's no concern so far from the parents or students," he said.
The Ministry of Health's website states that there were 1,478 new cases of TB among Singapore citizens and permanent residents last year, a slight increase from the 1,442 new cases in 2009.
Another Sec 4 student at Bedok Town told TNP in April that he tested positive in the Mantoux skin test.
But he did not have symptoms, so he was treated as a case of latent TB infection and given daily medication for nine months.
He told TNP yesterday that it was "annoying" in the beginning to take the medicine every morning.
"It would have been a bit of a bother if I was taking a major exam then, but it's better to be safe than sorry," he said.
"Now I'm used to it. Luckily, I don't suffer from any side effects such as fatigue.
This article was first published in The New Paper.