SciDev.Net

Chest X-ray of a patient with TB

WHO/STB/Colors Magazine/J. Mollison

[SINGAPORE] Researchers in Singapore have suggested that patients with severe acute respiratory syndrome (SARS) may run a higher-than-average risk of developing tuberculosis (TB).

During the SARS outbreak in 2003, doctors at the country's Tan Tock Seng hospital found that two out of 236 individuals diagnosed with 'probable' SARS were also infected with tuberculosis. Although small, this represents a far higher incidence rate than is commonly found in the general population.

"We think the patients developed TB after acquiring SARS," says C.C. Lee, one of the members of the research team, who report their finding in the medical journal Clinical Infectious Diseases. "To the best of our knowledge, this is the first documented case of its kind."

Tuberculosis is a bacterial infection that spreads through droplets in the air. When a person's immune system is working normally, the infection can remain inactive in the body for a long time without causing any symptoms to appear. The researchers suggest that the reduced immunity in SARS patients increases their susceptibility to tuberculosis.

According to their paper, the two patients found to be suffering from TB had previously been discharged from hospital, after having fully recovered from SARS. One then developed a dry cough and showed worsening lung conditions in follow-up chest X-rays; the other was recalled for treatment when he tested positive for the tuberculosis bacterium.

"When the result came back, we recalled the patient so that therapy could be started immediately," says Lee.

He points out that World Health Organisation guidelines for hospital discharge and follow-up for SARS patients stipulate that these should be given repeated chest X-rays until their health returns to normal. Following this guideline, he says, should allow doctors to diagnose TB infections, as the disease will be revealed by chest X-rays if left untreated.

But Lee told SciDev.Net that health services should be made aware that any physiological signs revealed by X-rays of recovering SARS patients could actually be caused by tuberculosis, rather then the original infection with SARS.

Reference: Clinical Infectious Diseases 38, 123 (2004)

Link to full paper by Low et al in Clinical Infectious Diseases