Rise in TB incidence due to ageing population, more foreigners: Study
SINGAPORE — A greying population and a rise in the number of foreigners have contributed to an increase in the incidence of tuberculosis (TB) in Singapore since 2008, a study led by researchers from the National University of Singapore (NUS) has found.
The incidence rate of TB — the number of new cases per population at risk, at a given time — had been on a downward trend in Singapore since 1998, even hitting a historic low of 35.1 cases per 100,000 people in 2007. But the number began to climb to around 39 cases per 100,000 people from 2008.
In their study, which was published in BioMed Central Public Health journal in October, the NUS researchers looked at more than 40,000 TB cases reported to the Singapore Tuberculosis Elimination Programme (STEP) registry between 1995 and 2011. They found that the higher incidence of the infectious respiratory disease among the elderly partly accounted for the increase in incidence of TB among Singapore residents; the resident elderly population here in 2011 was almost double its population in 1995.
The researchers also found that another contributor to the overall burden of TB here came from the growing non-resident population, who were found to have higher TB incidence rates than residents. Since around 2005, the liberalisation of Singapore’s immigration policy saw a marked increase in the foreign population here, noted the study.
“As you grow older, you also have conditions that weaken your immune system, and it’s the immune system that controls the tuberculosis bacteria,” said Dr Hsu Li Yang of the Saw Swee Hock School of Public Health at NUS, who led the study.
His colleague, Assistant Professor Alex Cook, said that though STEP — a programme started in 1997 under which a nurse or doctor supervises patients with their daily medication, while their relatives, friends and colleagues are screened — managed to better control the disease over the years, the effects of an ageing population remained bigger than the results of STEP efforts.
That is why the researchers noted that since 1995, the incidence rates of TB have been decreasing when compared across different age groups. This means that a 65-year-old in 2011 had a lower chance of getting TB as compared with an individual of the same age in 1995, for instance.
Meanwhile, the proportion of TB cases involving non-residents increased from 25.5 per cent in 1995 to 28.9 per cent in 2004 and 47.7 per cent in 2011.
“An increasing trend of non-resident TB cases contributing to the overall proportion of TB cases over the years could suggest that mass immigration from high TB incidence countries is increasingly contributing to the burden of TB in recent years in Singapore,” noted the study, which cited India and China as some of the countries of origin of these non-residents.
But while non-resident TB cases contributed to the overall TB rates here, the researchers did not find a direct link between the increase in the foreign population and the risk of TB among local residents.
With these findings, Dr Hsu noted that doctors in Singapore would have to be more aware of potential tuberculosis cases among the elderly. Already, foreign workers entering Singapore are undergoing stricter checks for TB, with their X-rays sent to the STEP registry, he added.
The World Health Organization (WHO) estimated that nine million people developed TB and 1.5 million died from the disease last year. Singapore sits within a region that accounts for 29 per cent of the global TB incidence. Though TB is slowly declining each year and it is estimated that 37 million lives were saved between 2000 and last year through effective diagnosis and treatment, the WHO noted that the death toll was still unacceptably high, given that most deaths from TB are preventable.