High proportion of extrapulmonary tuberculosis in a low prevalence setting: a retrospective cohort study

Objectives The proportion of extrapulmonary tuberculosis (EPTB) cases in the United States (US) has been rising due to a slower rate of decline in EPTB compared to pulmonary tuberculosis (PTB). The purpose of this study was to characterise the clinical and treatment differences between EPTB and PTB patients, and identify patient factors associated with EPTB. Study design We performed a retrospective cohort study of active tuberculosis (TB) cases treated at the Baltimore City Health Department between 2008 and 2013. Methods We categorised patients as having ‘only PTB’ (infection in the lung parenchyma), ‘EPTB/PTB’ (infection in the lung and an additional site), and ‘only EPTB’ (infection not involving the lung). Pearson's chi-squared tests were used to evaluate categorical variables and compare clinical and demographic differences between only PTB, only EPTB, and EPTB/PTB patients. Student t-tests and one-way analysis of variance tests were utilised to assess continuous variables and to compare treatment differences. Results One hundred and sixty-three patients were treated for TB; 39.3% had some form of EPTB (either EPTB/PTB or only EPTB). There was no difference found between EPTB, PTB, and EPTB/PTB patients with respect to HIV status, gender, race, foreign-born status, or mean age. Patients with only EPTB were less likely than patients with some form of PTB (only PTB or EPTB/PTB) to present with cough (30.4% vs 61.5%; P < 0.001), night sweats (10.9% vs 39.3%; P < 0.001), and weight loss (28.3% vs 47.9%; P = 0.023). Patients with some form of EPTB were also more likely to be hospitalised postdiagnosis compared to patients with only PTB (39.1% vs 20.2%; P = 0.009), and to have longer mean durations of treatment (37.9 weeks [SD = 11.1] vs 31.8 weeks [SD = 8.1]; P < 0.001). Conclusions EPTB patients present with atypical symptoms, undergo prolonged treatment, and experience increased hospitalisations. In order to improve diagnostic algorithms and treatment modalities, EPTB must be further characterised.