SINGAPORE - People with lupus, an autoimmune disease in which the immune system attacks normal, healthy tissue, have a higher risk of contracting tuberculosis, a local study has found.

In a study based on 301,000 patients admitted to Singapore General Hospital (SGH) between 2004 and 2011, the hospital found that 2 per cent of 840 patients who had lupus also had TB.

This is about five times higher than hospitalised patients without lupus.

The risk doubles to 10 times if lupus patients also have chronic conditions such as diabetes and hypertension.

In contrast, the incidence of TB among people here is between 0.035 per cent and 0.045 per cent.

The findings of the study were presented at a media briefing at SGH on Tuesday (Sept 26).

People with lupus can suffer from inflammation, swelling and damage to the skin, joints, heart, lungs, kidneys and nervous system.

The cause of lupus, however, remains unclear.

Treatment for lupus affecting the organs involves high doses of medication that suppresses the immune system.

This puts patients at risk of acquiring infections such as TB. Once infected with TB, lupus patients in remission have a higher rate of relapse and death, as TB mimics certain lupus symptoms, making it more difficult to diagnose and treat.

The study, published in the Rheumatology International journal in March, was conducted by researchers from SGH's departments of epidemiology, rheumatology and immunology, and infectious diseases.

Numerous studies overseas have associated lupus, or systemic lupus erythematosus, with an increased risk of contracting TB, but little had been known about the extent and possible risk factors of TB among lupus patients in Singapore, said Professor Julian Thumboo, a senior consultant at SGH's Department of Rheumatology and Immunology.