The epidemiology of tuberculosis in the Balimo region of Western Province, Papua New Guinea

Papua New Guinea (PNG) is a country of great diversity. The landscape and geography ranges from volcanic and mountainous highlands to coastal and floodplain lowlands, as well as more than 600 islands. There are more than 800 cultural and language groups countrywide, with more than 80% of the population living in rural areas (National Research Institute 2010). In 2016, tuberculosis (TB) in PNG was estimated to have caused more than 30,000 cases countrywide (World Health Organization 2017a), with control challenged by the emergence of drug resistance, and complicated by a resource-limited health system. The situation faced by PNG due to TB and drug-resistant TB (DR-TB) has been described as an emergency (Eccles 2016; IRIN 2010). Research from regional settings in PNG has described a TB burden much higher than the national average, including in Western Province where this study was based (Aia et al. 2018; Cross et al. 2014; McBryde 2012). However, there is limited epidemiological data from areas outside the South Fly and provincial capital of Daru, despite evidence of a heavy TB and drug-resistant TB (DR-TB) burden (Aia et al. 2016; Furin & Cox 2016; Kase et al. 2016; McBryde 2012). The research presented in this thesis describes and characterises the distribution and determinants of TB in the rural Balimo region of Western Province. It is hoped that this study will provide epidemiological data about TB in the region that can inform local TB control strategies. This study used retrospective data analysis and laboratory techniques to describe TB in the Balimo region. The Balimo District Hospital (BDH) TB patient register was analysed, and laboratory diagnostic results were examined. A molecular assay was used to describe genetic evidence of DR-TB, and an interferon (IFN)-ɣ release assay (IGRA) was used to investigate the population-level latent TB burden and Mycobacterium tuberculosis complex (MTBC) infection in TB patients. A very high burden of TB was identified, with an estimated incidence of 727 TB cases per 100,000 people per year. Approximately 25% of TB patients were children, and more than 75% of all patients had extrapulmonary TB. Spatial analysis of TB across the region identifed a high TB burden in the area immediately surrounding Balimo. Lower rates of TB were identified in more remote areas, likely due to the challenges faced by people from rural regions in accessing health facilities. However, the spatial analysis also provided evidence of potential under-diagnosis of TB in more remote areas. DR-TB was described in the region, based on molecular evidence of rifampicin (RIF) resistance. In addition, the challenges of diagnosing TB in this region, where laboratory facilities are limited, are highlighted based on validation of the smear microscopy method used at the BDH laboratory. In combination, these results emphasise the importance of implementing a molecular method of TB diagnosis and detection of drug resistance in the Balimo region. Given the high burden of TB described in the Balimo region, an unexpectedly low proportion of latent TB was identified. Analysis of the IGRA results provided support for the accuracy of extrapulmonary TB diagnoses at BDH, which is important given more than 90% of the extrapulmonary TB diagnoses in the TB register analysis were made clinically based only on presenting signs and symptoms. Overall, this study emphasises the very high burden of TB present in the Balimo region. The results highlight the critical importance of investing in the hospital at Balimo, and ensuring that resources and facilities at the hospital are of a high standard adequate for accurate diagnosis and effective management of TB in the region. This need is especially important in the context of a region where other infectious diseases are also endemic. As a broad epidemiological study of TB in the Balimo region, the results presented in this thesis contribute important contextual information and baseline data on which future TB control efforts can be based.