Health Ministry monitoring TB trends among foreign workers

4 May 2012, Today

Are our TB screening measures for foreign workers enough?

According to the report "Don't ignore TB in foreigners: Experts" (May 1), between 2004 and 2010, "there was a 46-per-cent spike in the total number of new TB cases notified in Singapore".

The proportion of foreigners increased from 29 per cent to 47 per cent of the total case burden. So I am concerned about how foreign workers here are screened for tuberculosis, which could have contributed to its resurgence.

According to a study published last year, after Singapore liberalised its immigration policy in 2005, "there was an influx of migrant workers and immigrants from countries with high incidences of TB and a corresponding increase in TB notifications among this population".

Of these persons with TB, more than 75 per cent came from five of the seven countries (India, China, Indonesia, Bangladesh and the Philippines) with highest incidences of TB.

The work permit health screening uses the chest X-ray as the screening tool for pulmonary TB. It does not include any other test for the detection of TB in these foreign workers.

However, the chest X-ray is known for its limits in detecting early disease or recurrences. Although it is commonly used for the diagnosis and screening of active TB, it has poor sensitivity, specificity and reproducibility.

One likely reason for a delay in diagnosis of TB is an over-reliance on X-rays.

A 2010 article in the journal Respirology cited how it became clear in Hong Kong that its general practitioners depended "too much on X-rays ... and that they were slow in referring TB patients to the government TB service".

Some cases of active pulmonary TB could be missed. To compound the problem, scarring from previously cured disease seen on X-rays might sometimes be difficult to distinguish from current active TB.

In conjunction with radiological evidence, the Centers for Disease Control and Prevention in the United States recommend at least a TB skin test or TB blood test.

Suspicious cases are also sent for further laboratory tests. This is reasonable since another study, in the journal Chest, found that "culture-positive pulmonary TB with a normal chest radiography is not uncommon" and that the incidence of this is increasing.

In other words, a patient with a normal chest X-ray could have active TB, which could go undiagnosed if no other tests are done.

If a foreign worker does not declare his symptoms accordingly, clinical suspicion would be lowered during the work permit health screening.

Combining a simple TB skin test with a chest X-ray would enhance the quality and effectiveness of TB screening in foreign workers.

Suspected cases would then be referred for further diagnostic tests (for example, sputum smears and cultures) to delineate those with latent TB infection from those with active TB disease.

Should not the Manpower Ministry change its practice of using merely a chest X-ray for TB screening in foreign workers?

Vincent Chia Wei Meng

Reply from MOH

14 May 2012, Today

Health Ministry monitoring TB trends among foreign workers

WE THANK Dr Vincent Chia for his feedback in the letter "Are our TB screening measures for foreign workers enough?" (May 4). Screening requirements for tuberculosis vary according to the TB situation in each country.

Our screening policy for foreign workers aims to detect lung TB (active TB disease of the lungs) before they start work here, as these are the infectious cases. Such cases can then be referred for prompt medical attention.

The vast majority of lung TB cases will have abnormalities in their chest X-rays and will thus be picked up during screening. Lung TB cases are required to undergo treatment under strict programmatic conditions (directly observed therapy).

We wish to clarify that the United States does not require a chest X-ray with blood test/skin test for lung TB screening. Our screening policy is, therefore, consistent with the US Center for Disease Control's recommendation for diagnosis of lung TB.

Dr Chia expressed concern that some TB cases may be missed due to lack of radiographic evidence of lung TB.

The current screening algorithm requires that high-risk individuals with ambiguous chest X-ray findings or scarring be referred to the national TB treatment centre, the TB Control Unit at Tan Tock Seng Hospital, for further assessment.

Even in the absence of bacteriological results for TB and/or symptoms, such individuals can be started on treatment based on radiological findings if the index of suspicion for TB is high.

We agree with Dr Chia that the TB screening process must be reviewed and tightened where possible. We will continue to monitor changes in TB disease trends in the foreign worker population, and to review and tighten screening requirements where necessary.

Greater efforts will also be made to educate and create awareness among foreign workers about TB and its symptoms so that they can seek medical attention early to prevent transmission in the community.

We urge employers to be supportive of TB treatment for their workers, by granting them the flexibility to go for treatment, when necessary.

Jeffery Cutter (Dr)
Director, Communicable Diseases Division
Ministry of Health