Our study provides the first detailed sub-national analysis of the epidemiological situation of TB in Sabah, Malaysia in recent years. Findings highlight the high burden of disease in Sabah compared with the rest of Malaysia. In 2018, the case notification rate in Sabah (128 cases per 100,000 population) was 47% higher than that of the national case notification rate of Malaysia (79 cases per 100,000 population). Our findings agree with WHO reports indicating that over the period of 2012 to 2018, the total number of cases in Sabah represented 20% of all TB notifications in Malaysia.(17) Sabah State is a setting which poses unique challenges to Malaysia’s national TB control program. Sabah is less economically developed than peninsular Malaysia, has an interior which can be topographically challenging and difficult to access for healthcare provision, has substantial communities of marginalised persons living in overcrowded informal settlements, and a porous land/sea border with the Philippines.(18) Understanding the local epidemiology in this unique context is critical to implementing effective measures for TB control and prevention.
Our results show that while Sabah has a moderate overall burden of TB, there were geographic hotspots of disease – particularly the districts of: Semporna, Pitas, Kota Marudu, Tuaran, and Kota Kinabalu. These districts correspond with areas of frequent cross-border movement between Malaysia and the Philippines (Semporna and Pitas) and the more populous urbanised districts of north-western Sabah (Tuaran, Kota Kinabalu and Kota Marudu). Given the high burden of TB in Sabah’s nearest two neighbours, the Philippines and Indonesia (incidences of 554 and 316 cases per 100,000 population respectively),(13) and the frequent movement of people across these international borders, there is an evident need for the Malaysian healthcare system to actively engage international arrivals in no-cost TB prevention and early detection strategies. It is difficult however, to ascertain the relative burdens of imported versus locally acquired TB disease. Our finding of geographic areas with a high proportion of cases among non-citizens, and high-burden urban areas with a relatively low proportion of cases among non-citizens, may support a hypothesis of seeding of overseas acquired disease in Sabah, with amplification of transmission occurring in densely populated urban centres. Investment in healthcare for non-citizens could therefore have a major beneficial impact on overall TB rates. Previous studies have shown that the majority of TB cases occur within two years of infection.(19, 20) However, we found that among overseas born TB cases, the majority developed TB five or more years after arrival in Sabah, further supporting the likelihood that transmission of TB, even among overseas born cases, is occurring locally.
Sabah’s migrant population, especially those who are refugees, from stateless minority groups and illegal or undocumented migrants face substantial challenges to accessing healthcare and social protection – including financial, legal, language and physical access barriers.(21–23) The finding that non-citizens were significantly more likely to have advanced disease on chest x-ray and be sputum smear positive at presentation, suggests they present late to health services.
The United Nations Sustainable Development Goals encourage countries to achieve universal health coverage.(24) The WHO’s End TB Strategy reinforces the role of universal health coverage in ensuring equal and unhindered access to early diagnosis and treatment of TB.(6) Understanding the barriers that both non-citizens and citizens of Malaysia may face in accessing TB services is essential, followed by engagement of communities and reorientation of services to ensure patient-centred care.(6) We found that monthly household income of TB cases in Sabah (MYR 1,000 or USD 250) was around one-quarter the median monthly household income across Sabah State (MYR 4,110 or USD 1,031 in 2016).(25) This highlights the risk of financial barriers limiting access to diagnosis and care. Patient cost surveys are a useful tool to better understand the direct and indirect financial impacts of TB on patients. We note that at time of writing, Malaysia is in the process of planning for a national TB patient cost survey.(26)
Our results highlight key gaps in the detection of TB in Sabah. We found that case detection among children was very low, with children aged less than 15 years accounting for only 4.6% of cases, despite that age-group accounting for 24% of the Sabah population and global estimates of disease burden suggesting that this age-group accounts for 11% of all TB cases.(1) Diagnosis of TB in children is challenging due to the paucibacillary nature of their disease.(27) As our findings show, the majority of cases among children are diagnosed clinically. This highlights the importance of clinicians being trained in symptom-based screening and diagnosis of TB in children and collection of appropriate diagnostic samples such as gastric lavage and induced sputum. Given the likely under-diagnosis of childhood TB in Sabah, TB contact investigation should be strengthened to improve early detection of childhood TB, while enabling scale-up of treatment for TB infection to prevent future cases among high-risk contacts.(28)
Uptake of WHO-recommended rapid diagnostics (GeneXpert®) for diagnosis of TB was limited. However, at the time of the study, national guidelines did not recommend GeneXpert® as a first-line diagnostic test for all suspected drug-sensitive TB cases.(29) Rapidly increasing GeneXpert® coverage should be a priority, especially given that a quarter of cases were not tested by culture, and of those cases that were, culture positivity was extremely low (26% among pulmonary cases). While culture negative pulmonary TB can be an indicator of early disease,(30) the concurrent findings of high sputum smear positivity and high proportion of cases with moderate-advanced disease on chest x-ray, suggest the low culture positivity rate may be related to sub-optimal test sensitivity in this setting, noted in Kota Kinabalu previously.(31)
The low coverage of GeneXpert® and high proportion of culture negative or not tested cases, raises concern of drug-resistant TB being missed. The 2018 WHO estimates for MDR-TB in Malaysia for both new (1.5% [1.2–1.9%]) and previously treated cases (3.1% [1.3–5.9%]),(13) are considerably higher than what we observed in Sabah. Fast tracking the scale up GeneXpert® coverage would not only aid in improving confirmation of drug-sensitive TB, but help ensure that rifampicin resistance is detected. While current cases of MDR-TB are low, the lack of testing limits our confidence in whether all cases are being detected. Adding to this concern are the poor treatment outcomes recorded among MDR-TB cases. Given one-third of all MDR-TB cases stopped or failed treatment, there is a risk that these cases may continue to be infectious and contribute to primary transmission of drug resistance in Sabah. Efforts to improve treatment outcomes among MDR-TB cases, such as through improved treatment supervision and monitoring, consideration of new all oral or standardised shorter regimens, and patient support measures should be prioritised.(32)
These findings are potentially limited by the quality and completeness of data recording and entry. Malaysia has a complex system of both paper based and electronic mechanisms for collection of patient data and notification of TB, and enumeration of cases may be imperfect. There was no scope to cross-check data from the myTB database against primary records. However, the State Department of Health undertakes regular auditing and cleaning of data to improve its quality and completeness. We note that case notification rates do not represent the true incidence of TB. In Malaysia, 13% of estimated incident TB cases in 2018 were not notified.(13) Thus our findings are likely to also underestimate the true burden of disease, particularly in some groups of the population which face additional barriers to care, such as those living in remote areas and migrants, particularly those without legal status.