Incidence and clinical significance of non-tuberculous mycobacteria among migrants in Denmark: A nationwide register-based cohort study from 1991 through 2021.

BACKGROUND: There is limited knowledge about non-tuberculous mycobacteria (NTM) infections in migrants. We aimed to assess the incidence and clinical significance of NTM among migrants in Denmark. METHOD: Nationwide register-based cohort study of migrants with a positive NTM culture in Denmark from 1991 through 2021, stratified by patient demographics, disease localisation, species, and clinical significance. RESULTS: 433 migrants had a positive NTM culture, resulting in an overall incidence rate (IR) of 3.7 (95%CI 3.3-4.0) per 100,000 migrants. Overall NTM IRs for definite disease were 1.0 (95%CI 0.9-1.2), possible disease 1.0 (95%CI 0.8-1.2), and isolation 1.7 (95%CI 1.4-1.9) per 100,000 migrants. Migrants had considerably higher age- and sex-adjusted NTM IRs of positive cultures (incidence rate ratio [IRR] = 2.1, 95%CI 1.9-2.3, p < 0.001), possible disease (IRR = 2.4, 95%CI 2.0-3.0, p < 0.001), and isolation (IRR = 4.6, 95%CI 3.9-5.4, p < 0.001) compared to Danish-born, but not of definite disease (IRR = 1.1, 95%CI 0.9-1.3, p = 0.562). IRs of migrants with positive NTM cultures did not increase over time (-0.8 %/year, p = 0.133). CONCLUSIONS: Migrants have a higher, but stable, burden of NTM compared with Danish-born. The higher rates likely reflect that more specimens are examined for Mycobacterium tuberculosis. Microbiologically classified definite NTM disease is not substantially more common among migrants.

Discovery and validation of a personalized risk predictor for incident tuberculosis in low transmission settings.

The risk of tuberculosis (TB) is variable among individuals with latent Mycobacterium tuberculosis infection (LTBI), but validated estimates of personalized risk are lacking. In pooled data from 18 systematically identified cohort studies from 20 countries, including 80,468 individuals tested for LTBI, 5-year cumulative incident TB risk among people with untreated LTBI was 15.6% (95% confidence interval (CI), 8.0-29.2%) among child contacts, 4.8% (95% CI, 3.0-7.7%) among adult contacts, 5.0% (95% CI, 1.6-14.5%) among migrants and 4.8% (95% CI, 1.5-14.3%) among immunocompromised groups. We confirmed highly variable estimates within risk groups, necessitating an individualized approach to risk stratification. Therefore, we developed a personalized risk predictor for incident TB (PERISKOPE-TB) that combines a quantitative measure of T cell sensitization and clinical covariates. Internal-external cross-validation of the model demonstrated a random effects meta-analysis C-statistic of 0.88 (95% CI, 0.82-0.93) for incident TB. In decision curve analysis, the model demonstrated clinical utility for targeting preventative treatment, compared to treating all, or no, people with LTBI. We challenge the current crude approach to TB risk estimation among people with LTBI in favor of our evidence-based and patient-centered method, in settings aiming for pre-elimination worldwide.

Nontuberculous mycobacteria in Denmark, incidence and clinical importance during the last quarter-century.

Disease caused by nontuberculous mycobacteria (NTM) is reported to increase due to an ageing population and a rise in the proportion of immunosuppressed patients. We did a retrospective cohort study of NTM-disease in the Danish population through a quarter-century to determine the disease burden and trends in annual incidence rates. 524,119 clinical specimens were cultured for mycobacteria from 1991 through 2015 at the International Reference Laboratory of Mycobacteriology in Denmark. Among these, 8,227 NTM strains were identified from 3,462 patients and distributed according to microbiological disease criteria. We observed no increase in NTM disease incidence or proportion of patients with positive NTM cultures during the study period (Quasi-Poisson regression, p = 0.275 and 0.352 respectively). Annual incidence rates were 1.20/105 for definite NTM disease, 0.49/105 for possible NTM disease and 0.88/105 for NTM colonization. The incidence rate of NTM disease was highest in children aged 0-4 years (5.36/105/year), predominantly with cervical Mycobacterium avium complex (MAC) adenitis. Surprisingly, based on more than half a million clinical specimens cultured for mycobacteria in Denmark through 25 years, the NTM disease burden and trend in incidence in the Danish population has not increased opposed to numerous internationals reports.

[Pulmonary infections with non-tuberculous mycobacteria].

In recent decades, an increasing incidence of pulmonary infections with non-tuberculous mycobacteria has been reported, primarily affecting patients with structural lung diseases and/or immunosuppression. In Denmark, approximately 100 new cases of infection with non-tuberculous mycobacteria occur yearly, most commonly with Mycobac-terium avium complex. Diagnosis is based on clinical, radiological and microbiological criteria. Treatment is difficult, and outcomes are often poor. Antibiotic treatment should be performed by specialists with reference to international guidelines.

Prognostic value of interferon-γ release assays, a population-based study from a TB low-incidence country.

BACKGROUND: The ability of interferon-γ release assays to predict the development of TB has been investigated in many studies, but few cases develop TB during follow-up limiting the generalisation of results. METHODS: We assessed QuantiFERON-TB Gold In-Tube test (QFT) results from 15 980 Danish individuals and data on all TB cases in Denmark from 2005 to 2012 and determined the predictive value of the QFT for coprevalent TB (0-90 days after testing) and incident TB (>90 days). RESULTS: Coprevalent TB was diagnosed in 10.7% (183/1703) and 0.3% (38/13 463) cases with a positive and negative QFT, respectively. For the QFT-positive cases, coprevalent TB was more frequent among persons <35 years compared with those >35  years (19.3% vs 7.2%, p<0.001). The cohort was followed-up for 52 807 person-years, median follow-up time was 3.36 years. For incident TB, the positive and negative predictive values (PPV and NPV) were 1.32% and 99.85%, respectively. Incidence rates (IR) for incident TB among QFT-positives and QFT-negatives were 383 per 10(5) and 45 per 10(5) person-years, respectively. Among cases with a positive QFT, IR for incident TB was associated with time interval since QFT (<2 years, p<0.001), but not with age (<35 years, p=0.087). CONCLUSIONS: We confirmed a high NPV of the QFT and found positive QFT associated with a higher risk of subsequent incident TB. Overall, the PPV for incident cases was 1.32%, and development of incident TB was associated with time interval after the QFT, but not with age.

QuantiFERON­TB Gold In-Tube test performance in Denmark.

BACKGROUND: Little is known about the QuantiFERON-TB Gold In-Tube Test (QFT) in extreme age groups. The test performance has been reported to be impaired in children and elderly, but reports are diverging. The aim of this study was to evaluate QFT performance in patients with and without Tuberculosis (TB). METHODS: A retrospective study analysing the results of 18,850 QFT performed in Denmark 2005-2010. The effect of age, sex, localisation of TB, and result of culture on QFT performance (positive, negative and indeterminate results) was determined. RESULTS: Among 383 patients with TB, indeterminate rate was low (3.9%, 15/383). Sensitivity was high (86.1%, 317/368) and not affected by sex or localization of TB disease, but declined with increasing age (p < 0.0001). In children 1-4 years old, sensitivity was high (100%, 9/9). Among 15,709 persons without TB, the indeterminate rate was 5.1% (804/15,709) and significantly higher in infants <1 year (15.6%, 5/32) and elderly >65 years (8.1%, 219/2715) compared to the adult population 15-64 years (4.5%, 552/12,317). Indeterminate results were due to a low positive control in 99.6% (801/804). CONCLUSION: In Denmark, a TB low incidence country, the overall QFT performance was good. The sensitivity in children (≥ 1) was high although few children were included, whereas sensitivity declined with increasing age. Indeterminate rates were higher in infants and elderly. In contrast to current guidelines, our data suggest that the QFT performs well in children ≥ 1 years in low endemic regions but that the test should be used with care among the elderly.

Development of a one-step probe based molecular assay for rapid immunodiagnosis of infection with M. tuberculosis using dried blood spots.

BACKGROUND: Antigen specific release of IP-10 is the most promising alternative marker to IFN-γ for infection with M. tuberculosis. Compared to Interferon-γ release assays (IGRA), IP-10 is released in high levels enabling novel approaches such as field friendly dried blood spots (DBS) and molecular detection. AIM: To develop a robust IP-10 based molecular assay for the diagnosis of infection with M. tubercuolsis from whole blood and DBS. METHOD: We developed a one-step probe based multiplex RT-qPCR assay for detecting IP-10 and IFN-γ mRNA expression from whole blood and DBS samples. The assay was validated and applied for the diagnosis of M. tuberculosis infection in DBS samples from 43 patients with confirmed TB, 13 patients with latent TB and 96 presumed uninfected controls. In parallel, IP-10 and INF-γ levels were measured in Quantiferon (QFT-TB) plasma supernatants. RESULTS: IP-10 mRNA upregulation was detectable at 4 hours after stimulation (6 fold upregulation) peaking at 8 hours (108 fold upregulation). IFN-γ expression occurred in concert but levels were lower (peak 6.7 fold upregulation). IP-10 gene expression level was significantly higher in patients with tuberculosis (median 31.2, IQR 10.7-67.0) and persons with latent tuberculosis infection (LTBI) (41.2, IQR 9.8-64.9) compared to healthy controls (1.6, IQR 1.1-2.4; p<0.0001). The IP-10 mRNA and protein based tests had comparable diagnostic accuracy to QFT-TB, sensitivity (85% and 88% vs 85%) and specificity (96% and 96% vs 97%, p = ns.). CONCLUSION: We developed a rapid, robust and accurate molecular immunodiagnostic test for M. tuberculosis infection. By combining DBS based sample acquisition, mail or currier based sample transport with centralized molecular detection, this immunodiagnostic test concept can reduce the local technological requirements everywhere and make it possible to offer highly accurate immunodiagnostic tests in low resource settings.

Non-tuberculous mycobacteria and the performance of interferon gamma release assays in Denmark.

BACKGROUND: The QuantiFERON-TB-Gold Test (QFT) is more specific than the Mantoux skin-test to discriminate between Mycobacterium tuberculosis (MTB) and non-tuberculous mycobacterial (NTM) infections. Here we study the performance of the QFT in patients with NTM disease. METHODS: From 2005 to 2011, nationwide patient data on positive NTM cultures (n = 925) were combined with nationwide data on QFT results (n = 16,133), both retrieved from the International Reference Laboratory of Mycobacteriology, Denmark. A total of 112 patients with NTM infections had a QFT performed, 53 patients had definite NTM disease, 10 had possible disease and 49 had NTM colonization. RESULTS: QFT was positive in 8% (4/53) of patients with definite disease, 40% (4/10) with possible disease and 31% (15/49) with colonization. Positivity rate was lowest among patients with definite disease infected with NTM without the RD1 region 4% (2/50). None of the 15 children with MAC lymphadenitis had a positive QFT. CONCLUSION: This study is one of the largest assessing IGRAs in patients with NTM disease in a TB low-incidence setting. Our study showed that the QFT holds potential to discriminate between NTM and MTB infections. We found no positive IGRA test results among children with NTM not sharing the RD1-region of MTB resulting in a 100% specificity and we suggest that a QFT in a child presenting with cervical lymphadenitis may be helpful in distinguishing NTM from TB lymphadenitis.

Negative effect of smoking on the performance of the QuantiFERON TB gold in tube test.

BACKGROUND: False negative and indeterminate Interferon Gamma Release Assay (IGRA) results are a well documented problem. Cigarette smoking is known to increase the risk of tuberculosis (TB) and to impair Interferon-gamma (IFN-γ) responses to antigenic challenge, but the impact of smoking on IGRA performance is not known. The aim of this study was to evaluate the effect of smoking on IGRA performance in TB patients in a low and high TB prevalence setting respectively. METHODS: Patients with confirmed TB from Denmark (DK, n = 34; 20 smokers) and Tanzania (TZ, n = 172; 23 smokers) were tested with the QuantiFERON-TB Gold In tube (QFT). Median IFN-γ level in smokers and non smokers were compared and smoking was analysed as a risk factor for false negative and indeterminate QFT results. RESULTS: Smokers from both DK and TZ had lower IFN-γ antigen responses (median 0.9 vs. 4.2 IU/ml, p = 0.04 and 0.4 vs. 1.6, p < 0.01), less positive (50 vs. 86%, p = 0.03 and 48 vs. 75%, p < 0.01) and more false negative (45 vs. 0%, p < 0.01 and 26 vs. 11%, p = 0.04) QFT results. In Tanzanian patients, logistic regression analysis adjusted for sex, age, HIV and alcohol consumption showed an association of smoking with false negative (OR 17.1, CI: 3.0-99.1, p < 0.01) and indeterminate QFT results (OR 5.1, CI: 1.2-21.3, p = 0.02). CONCLUSIONS: Cigarette smoking was associated with false negative and indeterminate IGRA results in both a high and a low TB endemic setting independent of HIV status.