Epidemiology of tuberculous lymphadenitis in Denmark: A nationwide register-based study

BACKGROUND: Tuberculous lymphadenitis (TBLA) is the most common extrapulmonary manifestation of tuberculosis (TB), often claimed to be reactivation. We aimed to describe the epidemiology of TBLA in Denmark, as it has not previously been investigated specifically although extrapulmonary TB has been associated with an increased long-term mortality and delays in the diagnosis. METHODS: Register-based study of all patients notified with TBLA in Denmark from 2007 through 2016 utilizing six different nationwide registers. Patients were identified through the national TB surveillance register, and the diagnosis evaluated based on microbiology, pathology and/or clinical assessment. RESULTS: In total, 13.5% (n = 489) of all TB patients in Denmark had TBLA with annual proportions from 9.4 to 15.7%. Most patients were immigrants between 25–44 years. Incidence rates ranged from as high as 1,014/100,000 for Nepalese citizens to as a low as 0.06/100,000 for Danes. Danes had a significant higher median age and significant more risk factors and comorbidities, as well as an increased overall mortality, compared with immigrants (p<0.05). A significant and much higher proportion of unique MIRU-VNTR genotypes were seen among TBLA patients compared to other TB manifestations. CONCLUSION: In Denmark, TBLA is a common manifestation of TB, especially in young immigrants from high-incidence countries. In Danes, it is a rare disease manifestation and associated with higher morbidity and mortality. To our knowledge, this is the first study suggesting that TBLA is predominantly associated with reactivation of latent TB infection based on genotyping although this remains to be clarified.