While the COVID-19 pandemic has shifted the world’s attention and other chronic diseases continue to demand our attention, the annual World TB Day serves as a reminder of the catastrophic health, social and economic consequences of TB. This ancient disease killed 1.6 million people in 2021 and devastated more lives.

“But I thought tuberculosis no longer existed, or at least, not in Singapore”

Tuberculosis (TB) is endemic in Singapore. We saw a 7.9% increase in TB cases between 2015 and 2021.

Why are we seeing a gradual increase in TB cases in a high-income country with a relatively equitable healthcare system?

Erasing the gains of TB control and management in Singapore

Since 1957 when the country established the TB Control Unit and kickstarted the National TB Programme, TB incidence rates plummeted until the rate stagnated in the late 1980s to early 1990s.

TB incidence in Singapore declined again in the mid-1990s with the Singapore TB Elimination Programme (STEP) implementation. Strategies to eliminate TB were focused on active TB treatment monitoring and surveillance and latent tuberculosis infection (LTBI) screening of close contacts of active TB cases.

Between 1998 and 2007, TB rates in Singapore decreased from 58/100,000 to 35/100,000. However, TB incidence rates increased to 48/100,000 in 2021.

This trend reversal will continue if the government does not introduce more measures to lower TB incidence in the country, erasing all efforts in the last 20 years.

TB is an opportunistic infection

Reactivation from LTBI to active TB occurs due to weakened immune systems.

Infections occur among those with weakened immune systems, such as the elderly and immunocompromised. Those at most risk are diabetic; on dialysis; have immune-mediated inflammatory diseases requiring biologic treatment; organ transplant recipients, and people living with HIV (PLHIV).

TB-co-occurrence with another chronic disease increases the complexity of disease management for the immunocompromised and immunosuppressed. Multi-drug resistant TB is also on the rise. These complexities add to the patient’s healthcare costs and add more pressure to our healthcare system.

Many elderly Singaporeans acquired LTBI in the 1950s and 1960s when Singapore’s TB rates were high. With age-related changes to their immune system, the elderly are more vulnerable to infections and other illnesses. As a result, their risk of latent TB reactivation to active TB is high.

As we enter the third year of the COVID-19 pandemic, growing cases of COVID-TB co-infection in Southeast Asia begin to emerge. While there is no official data on the number of COVID-TB co-infection cases, clinicians we work with in the region have voiced their concerns.

We have not fully understood the immune-pathological interaction between these diseases and drivers of dual COVID-19 and TB disease mortality. Moreover, studies from South Africa¹ and the Philippines² suggest that COVID-19 patients with TB have a higher mortality risk than COVID-19 patients without TB.

Managing “imported tuberculosis”

Additionally, Singapore’s reliance on a foreign workforce – both professional and blue-collared labour – from neighbouring countries increases the country’s vulnerability to “imported TB”.

Due to the greater global mobility of people brought about by socioeconomics, civil war, geopolitical conflicts, and climate change, managing “imported TB” isn’t a new phenomenon. Western industrialised countries with more liberal immigration policies face similar problems. However, how these countries decide to manage “imported TB” differs from Singapore, and that’s the difference.*

In a study conducted in Singapore on whether screening and treating foreign workers for LTBI is cost-effective³, one of the critical criteria used is the length of stay. The authors recommended that policymakers review the impact on health budgets and the health system’s capacity to support such an intervention.

But should the decision on whether to screen and treat the foreign workforce be solely made on costs alone without considering the catastrophic cost TB has on the infected individual and their families?

In a similar study in the UK to determine the cost effectiveness in latent TB screening among immigrants, the study found that new entrants to the UK have a high prevalence of LTBI as they arrive primarily from countries with the highest burdens of TB. The study concluded that using IGRA tests, the cost of implementing LTBI screening using an IGRA is cost-effective at a level of incidence that identifies most immigrants with LTBI⁴. This approach will prevent substantial numbers of future cases of active TB.

Why do we need to revisit current TB guidelines

South Korea has the highest TB prevalence among OECD (Organisation for Economic Co-operation and Development) countries.

However, since 2017, through significant funding, political will, new diagnostic technologies, and mass LTBI screening of selected groups of people based on their occupation and living conditions including day care centres, students, healthcare workers, postnatal care workers, and the military, the country achieved a new TB control target of 40 new cases per 100,000 people in 2022.

South Korea is setting a bold goal of reducing the number of TB cases to 20 per 100,000 people in the next five years, effectively reaching the TB elimination phase. The country has identified that preventing TB through LTBI control is essential to achieving these new targets. LTBI control initiatives are based on risk assessment.

Singapore’s LTBI guideline since 2019 has expanded the use of IGRA tests to screen people at high risk of developing active TB who are immunocompromised. However, the recommendations fell short in screening and treating those who live or work in congregated settings and recent migrants from high TB burden countries.

In recent years, the TB incidence rate in Singapore increased from 35/100,000 in 2007 to 48/100,000 in 2021. Between 2018 and 2020, about 300 foreign domestic workers were diagnosed with active TB after they started work.

We cannot ignore our country’s changing demographics – a rapidly ageing population with declining birth rates. Almost half of the country’s population are migrants from Malaysia (an intermediate TB burden country), and the rest are from high TB burden countries.

TB control strategy, which includes the prevention of reactivation of LTBI should be applied to any high-risk, vulnerable populations. Similar to Australia’s TB control strategy, a pre-entry screening and post-arrival follow-up among the migrant population for long-term resident and work visas could be implemented.

During the height of the COVID-19 pandemic, Singapore and many other countries enacted border control measures requiring pre-departure and post-arrival testing.

It would be remiss to compare the risk of an unknown virus during a pandemic to the risk of a known bacteria in an epidemic setting to enact such measures.

But what sets the TB epidemic apart from the COVID-19 pandemic is that early identification and preventative treatment for individuals with LTBI, and a proactive approach to screening LTBI can influence the future of global prevention of TB infection. Moreover, for the infected individual, the cascading effects on their health, quality of life and productivity are devastating when LTBI is reactivated to active TB.

It would be naïve not to address the potential pitfalls of this strategy where LTBI screening could be misused or misinterpreted as an inadmissible condition to the country – a topic that deserves a separate discussion.

Eradicating TB: Closing the gap on community transmission

In our high-income country, we need to revisit the argument about feasibility and cost-effectiveness of screening latent TB among the most vulnerable in our community.

As an intermediate TB burden country, we must rethink our TB control strategy and complacency in addressing the TB epidemic.

We need to effectively close the window of opportunity to reduce the prevalence of TB co-infection and the reactivation of latent TB to active TB.

We need to close the gap to end community transmission.

A recent study in Ireland – a low-incidence TB country — found that by not reaching the WHO End TB Strategy target between 2022 and 2035, the country will see 989 people having TB disease and 35 deaths; the cost of not meeting the End TB target is projected to be €70.779 million. Therefore, the study concluded that investment in effective interventions to reduce the burden of TB in Ireland is financially justifiable.⁵

The study also recommended expanding programmatic LTBI screening and treatment to include vulnerable populations, especially the marginalised, beyond those currently recommended for screening and treatment. 

How Singapore approaches TB management and control over the next five to ten years will determine whether we can eliminate TB in Singapore and our role as a global citizen in global TB control.

Note:

*Latent TB infection screening programmes of recent migrants exist in Norway, the Netherlands, Switzerland, Sweden, Denmark, France, the UK, Italy and Germany. Most countries in Europe have programmes for raising awareness of TB at the community care level.