By Dr Deborah Ng, Deputy Director, and Assoc Prof Jeffery Cutter, Acting Director of the National Tuberculosis Programme, National Centre for Infectious Diseases
The DOTS strategy
After the World Health Organization (WHO) declared tuberculosis (TB) a global emergency in 1993, it launched the Directly Observed Therapy Short Course (DOTS) as its strategy for controlling TB. The DOTS strategy was a comprehensive strategy that aimed to ensure care to most people with TB disease presenting to primary care health services, and was composed of five main prongs:1,2
- Government commitment to ensuring sustained, comprehensive TB control activities;
- Case detection by sputum smear microscopy among symptomatic patients self-reporting to health services;
- Standardised short-course chemotherapy using regimens
of six to eight months for at least all confirmed smear- positive cases, including DOT for certain categories;
- Regular uninterrupted supply of all essential anti-TB drugs;
- Standardised recording and reporting system that allows assessment of case-finding and treatment results for each patient and of the TB control programme performance overall.
The need for a new strategy
One of the key aspects of this strategy included case detection by sputum smear microscopy among symptomatic patients. However, the stagnating rates of TB globally led stakeholders to re-examine the effectiveness of this strategy. In fact, findings show that while the DOTS strategy improved overall treatment success, it had no effect on case detection.3 As a result, the WHO devised a new strategy in 2015, termed the ‘End TB Strategy’, adopted by the World Health Assembly in 2014, with the aim of ending the TB epidemic by the year 2030.4 As part of this new strategy, it was recognised that the focus on smear-positive cases alone was insufficient to reduce TB incidence. The strategy was therefore expanded to include not only systematic screening of contacts, but also high risk groups, and the need to scale up preventive treatment (PT) among persons at high risk of TB.
The strategy also set out intermediate milestones, setting the targets of a 20% reduction in TB incidence rate, 35% reduction in TB deaths and having zero catastrophic costs by 2020. According to the Global TB report 2021, there has only been a 11% reduction in TB incidence rate, 9.2% reduction in TB deaths, and 47% of people with TB still facing catastrophic costs worldwide.5 While some setbacks in achieving these targets have been contributed by the COVID-19 pandemic, it is essential to know if the strategies that have been laid out can achieve the desired targets in mind.
But the question is, what are these strategies and what needs to be changed? First, a paradigm shift in our understanding of TB is needed. In recent years, the definition of TB infection has evolved from a dichotomy of active and latent TB to a continuum of TB disease, whereby there are populations of persons with subclinical TB who may have no or unrecognized symptoms, but still potentially infectious.6 While these groups may not be highly infectious, they represent a gap in current public health strategies that need to be addressed, in order to achieve the target of ending TB.
The second is to adjust existing public health strategies. In order to achieve this ambitious goal of reducing the TB incidence by more than a thousand fold from 1,280 cases per million in 2010 to one case per million globally by 2050, new strategies must be deployed. Short of an effective vaccine, it is essential to maximize the use of all available tools that we have now in our armament to achieve these goals. A modelling study by Dye et al7 found that only a combined approach of targeting active and latent TB could produce a synergistic result to help achieve the goal of TB elimination. This means effective treatment of active TB with early case detection and high diagnostic accuracy, combined with the widespread scale up of PT.
Locally, contact tracing is already being expanded to screen more contacts, detect more cases of latent tuberculosis infection (LTBI) and treat them. This has been complemented by the use of whole genome sequencing to carry out targeted mass screening exercises where clusters of TB cases have been detected. As our knowledge and understanding of TB continues to evolve, and we continue to update our strategies to reflect the changing tides, we can look forward to bring an end to this epidemic in Singapore and worldwide eventually.
- World Health Organization. Stop TB at the source, Geneva, WHO, 1995.
- World Health Organization. Use DOTS more widely. Geneva, WHO, 1997.
- Obermeyer Z et al. Has the DOTS strategy improved case finding or treatment success? An empirical assessment. PLoS One 2008.
- World Health Organization. The End TB Strategy. Geneva, WHO, 18 August 2015.
- World Health Organization Global TB Report 2021. WHO Geneva.
- Migliori GB, Ong CWM, Petrone L et al. The definition of tuberculosis infection based on the spectrum of tuberculosis disease. Breathe 2021; 17: 210079.
- Dye C, Glaziou P, Floyd K, Raviglione M, et al. Prospects for tuberculosis elimination. Annu. Rev. Public Health 2013; 34: 271 – 86.
The article was also published in Volume 1 of Infectious Disease Intelligence here.