People with lupus – a disease in which the immune system attacks normal, healthy tissue – have a higher risk of contracting tuberculosis (TB), a local study has found.

A study based on 301,000 patients aged 21 and older, admitted to Singapore General Hospital (SGH) between 2004 and 2011, found that 2 per cent of 840 patients who had lupus also had TB.

This is about five times higher than for 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 study findings were presented at SGH yesterday.

TB is an airborne disease that is spread through close and prolonged contact with a person with the active form of the disease.

The incidence of TB here has been declining, from 40.8 cases per 100,000 population in 2002, to 36.1 cases per 100,000 population in 2015, according to the Health Ministry’s Communicable Diseases Surveillance in Singapore 2015 report.

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.

There are about 4,000 to 5,000 lupus patients here, and SGH currently has around 800.

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.

Said Professor Julian Thumboo, a senior consultant at SGH’s Department of Rheumatology and Immunology: “TB mimics some lupus symptoms, such as fever, joint pain and excess fluid around the lungs, so it can be challenging to diagnose.”

This can cause a delay in the diagnosis and treatment of TB, resulting in lupus patients with TB having a higher rate of relapse and death, he added.

The similarity in symptoms was a major reason why lupus patient Kartina Mohamad, 44, did not realise she had contracted TB in 2009.

“I usually get coughs and fever once a month (due to lupus), but that time, it persisted for three months,” said the customer service officer. By that time, her son, then 11, had become infected with TB as well, though both mother and son recovered in six months after receiving treatment.

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.