Epidemiology of Extrapulmonary Tuberculosis in Brunei Darussalam: A retrospective cohort study

Abstract Objectives We reported the incidence and associated factors of extrapulmonary tuberculosis (EPTB). Design A retrospective cohort study. Setting Brunei Darussalam, an intermediate tuberculosis (TB)-burden country with stagnating annual TB rates. Participants All active TB cases identified in the country between January 2001 and December 2018 (18 years) Primary and secondary outcome measures Annual proportions of EPTB (overall and specific) were calculated. Multiple logistic regression was done to investigate factors associated with developing EPTB, when compared to pulmonary TB (PTB). Chi-square trend test was used to determine any trends during the 18-year study period. Results We identified 3,916 TB cases, among which 743 (19.0%) were EPTB cases. Lymphatic (44.8%) and pleural (19.4%) EPTB were most common. The main modes of diagnosis were tissue biopsy (73.6%) and radiologic assessment (18.3%). Treatment success and mortality rate were 79.7% and 7.0%, respectively. Associations with specific EPTB types varies with age-group and gender. Younger age-group (adjusted Odds Ratio [aOR] ≥1.94) and females (aOR: 2.45 [95%CI: 1.94,3.11]) had higher adjusted odds of developing lymphatic EPTB, but had lower adjusted odds of developing pleural EPTB [younger age-group (aOR ≤0.54) and female (aOR: 0.41 [95%CI: 0.17,0.90])]. When compared to foreign residents, locals had higher adjusted odds of skeletal (aOR: 4.44 [95%CI: 2.04,11.69]), gastrointestinal (aOR: 3.91 [95%CI: 1.84,9.66]) and other types of EPTB (aOR: 3.42 [95%CI: 1.53,9.14]). No significant trend differences were observed for overall and specific EPTB types. Conclusion Despite being generally non-infectious and less recognised than PTB, understanding EPTB epidemiology is important as it also contributes to the overall TB burden in a country. Examining EPTB cases by their specific anatomical site would provide more information on risk factors. Raising public awareness on the EPTB symptoms and that TB affects lungs and other parts of the body could promote early health seeking behaviour and early EPTB diagnosis. Strengths and limitations of this study - We analysed TB case notification data, retrospectively collected as part of the national TB surveillance programme. - The main study strength is the length of the study period (18 years) and that all notified TB cases in the country were captured in this dataset. - Study limitations include the inability to distinguish between PTB cases with only lung involvement and those with miliary TB and/or concurrent PTB and EPTB, and also the inability to include data on co-morbidities.