Screening for TB by sputum culture in high-risk groups in Copenhagen, Denmark: a novel and promising approach.

INTRODUCTION: Evidence on screening high-risk groups for TB by mobile X-ray in low-incidence countries is building, but knowledge on other possible screening methods is limited. In this retrospective study we report results from a community based programme screening for TB by spot sputum culture. METHODS: On seven occasions, from September 2012 through June 2014, we offered TB screening to all persons present at 11 locations where socially marginalised people gather in Copenhagen. Spot sputum samples from participants were examined by smear microscopy and culture. Genotype, nucleic acid amplification test and chest X-ray were done if TB was found. RESULTS: Among 1075 participants, we identified 36 cases of TB. Twenty-four cases (66.7%) were identified at the first screening of each participant, that is, the prevalence of TB was 2233/100 000. Thirty-five (97%) of the TB cases were culture-positive and seven (19.4%) were smear-positive. Twelve out of 21 (57.1%) cases tested were nucleic acid amplification test positive. Twenty-eight (77.8%) had chest X-ray suggestive of TB. All patients with TB started treatment, 30 (83.3%) had a successful outcome. DISCUSSION: Screening for TB by spot sputum culture is possible and a promising alternative to mobile X-ray in a community based screening programme. 22.2% did not have chest X-ray suggestive of TB and would not have been identified using mobile X-ray. Most of the TB cases were smear-negative, suggesting that they were identified at an early, less infectious stage, which is essential in order to prevent transmission and gain infection control.

Migrant tuberculosis: the extent of transmission in a low burden country.

BACKGROUND: Human migration caused by political unrest, wars and poverty is a major topic in international health. Infectious diseases like tuberculosis follow their host, with potential impact on both the migrants and the population in the recipient countries. In this study, we evaluate Mycobacterium tuberculosis transmission between the national population and migrants in Denmark. METHODS: Register study based on IS6110-RFLP results from nationwide genotyping of tuberculosis cases during 1992 through 2004. Cases with 100% identical genotypes were defined as clustered and part of a transmission chain. Origin of clusters involving both Danes and migrants was defined as Danish/migrant/uncertain. Subsequently, the proportion of cases likely infected by the "opposite" ethnic group was estimated. RESULTS: 4,631 cases were included, representing 99% of culture confirmed cases during 1992 through 2004. Migrants contributed 61.6% of cases. Up to 7.9% (95% CI 7.0-8.9) of migrants were infected by Danes. The corresponding figure was 5.8% (95% CI 4.8-7.0) for Danes. Thus, transmission from Danes to migrants occurred up to 2.5 (95% CI 1.8-3.5) times more frequent than vice versa (OR = 1). A dominant strain, Cluster-2, was almost exclusively found in Danes, particular younger-middle-aged males. CONCLUSIONS: Transmission between Danes and migrants is limited, and risk of being infected by the "opposite" ethnic group is highest for migrants. TB-control efforts should focus on continues micro-epidemics, e.g. with Cluster-2 in Danes, prevention of reactivation TB in high-risk migrants, and outbreaks in socially marginalized migrants, such as Somalis and Greenlanders. Fears that TB in migrants poses a threat for resident Danes seem exaggerated and unjustified. We believe this to be true for other low incidence countries as well.

Characteristics of non-clustered tuberculosis in a low burden country.

Molecular genotyping studies often focus on clustered tuberculosis and recent transmission. Less attention has been paid to non-clustered tuberculosis. However, non-clustered cases also contribute significantly to the tuberculosis burden, especially in low-incidence countries. The objective of this study is to characterize non-clustered tuberculosis cases in Denmark and point out potential implications for tuberculosis control. The study is based on nationwide IS6110-RFLP genotyping of tuberculosis cases from 1992 through 2004, corresponding to 98% of culture verified cases. Of 3988 cases, 45% were non-clustered. Both Danes and immigrants had a peak incidence of non-clustered tuberculosis at older ages, 80-89 years (4.3 cases/10(5) population/year) and 60-69 years (28.8 cases/10(5) population/year), respectively. In addition, immigrants had a peak at 20-29 years (43.2 cases/10(5) inhabitants/year). In Danes, the incidence of non-clustered tuberculosis decreased during the study period and was predominantly found in elderly persons, presumably reactivating infection acquired during 1910-40, when tuberculosis incidence was high. In immigrants, the incidence was high at all ages, presumably reflecting reactivation of imported infections. In the future, the number of non-clustered tuberculosis cases will decrease, as older Danes die, and as time since primary infection increases for immigrants residing in Denmark. TB control should include focus on non-clustered cases.

Prospective evaluation of a whole-blood test using Mycobacterium tuberculosis-specific antigens ESAT-6 and CFP-10 for diagnosis of active tuberculosis.

A new immunodiagnostic test based on the Mycobacterium tuberculosis-specific antigens CFP-10/ESAT-6(QFT-RD1) has been launched as an aid in the diagnosis of latent tuberculosis (TB) infection (LTBI). The aim of this study was to evaluate this test for the diagnosis of active TB. Eighty-two patients with suspicion of TB and 39 healthy BCG-vaccinated persons were enrolled. Forty-eight had active TB, 25 did not, and 9 were excluded. Sensitivity and specificity of the test for active TB were evaluated in a prospective blinded manner in patients suspected of TB. The sensitivity of the QFT-RD1 was 85% (40/48; confidence interval [CI], 75 to 96), and it was higher than the sensitivity of microscopy, 42% (20/48; CI, 27 to 56; P = 0.001), and culture, 59% (27/46; CI, 44 to 73; P = 0.009). Of patients with extrapulmonary TB, 92% (12/13) were QFT-RD1 positive, whereas only 31% (4/13) were positive by microscopy and 42% (5/12) by culture (P < 0.05), and 87% (13/15) of those who were negative by both microscopy and culture were QFT-RD1 positive. By combining microscopy and culture with the QFT-RD1 test, sensitivity increased to 96% (CI, 90 to 102). Ten of 25 (40%) non-TB patients were QFT-RD1 positive, resulting in a specificity of 60%. However, 80% (8/10) of these had risk-factors for TB, indicating latent infection in this group. In healthy controls, only 3% (1/39) were QFT-RD1 positive. In conclusion, the QFT-RD1 test is sensitive for diagnosis of TB, especially in patients with negative microscopy and culture. The accuracy of the QFT-RD1 test will vary with the prevalence of LTBI. We suggest that the QFT-RD1 test could be a very useful supplementary tool for the diagnosis of TB.

Mannose-binding lectin polymorphisms in clinical tuberculosis.

Mannose-binding lectin (MBL) mediates protection against infections by using the complement system, but certain microorganisms may increase infectivity by exploiting this host defense system. Thus, it has been speculated whether genetically determined low MBL levels may confer partial protection against certain intracellular microorganisms, such as Mycobacterium tuberculosis. We investigated MBL alleles in 109 culture-positive human immunodeficiency virus-uninfected patients with tuberculosis living in Denmark and 250 white control subjects. Patients and control subjects were divided into 3 different groups defined by undetectable, low, and high serum MBL concentrations, which correlates to deficient, low, and high expressing MBL genotypes. A significantly decreased frequency of patients with the low-expressing MBL genotype was observed in white patients compared to control subjects. The same tendency also was observed in patients of other ethnic origin. It may be hypothesized that heterozygosity for MBL variant alleles, which encodes low serum MBL levels, is associated with protection against clinical tuberculosis.

Natural resistance-associated macrophage protein 1 polymorphisms are associated with microscopy-positive tuberculosis.

The natural resistance-associated macrophage protein 1 (NRAMP1) is implicated in the pathophysiology of mycobacterial infections. We investigated by polymerase chain reaction previously published Nramp1 genotypes at 4 loci-INT4, N543D, 3'UTR, and 5'(CA)(n) microsatellite markers-in 104 human immunodeficiency virus-negative patients with tuberculosis and 176 healthy control subjects living in Denmark. No significant difference in genotype frequency was found between white patients with tuberculosis and control subjects (P>.16), but carriage of Nramp1 variant alleles at loci INT4 and 5'(CA)(n) conferred a significantly increased risk of having microscopy-positive compared with microscopy-negative tuberculosis (65% vs. 35% [P=.0004] and 63% vs. 38% [P=.047], respectively). The Nramp1 alleles were not associated with increased risk for the development of cavities seen on chest radiographs, or with extrapulmonary tuberculosis. These results indicate that variant alleles in the Nramp1 gene are associated with increased mycobacterial replication rather than susceptibility for tuberculosis and may thus confer increased risk of severe disease.

Persistent high incidence of tuberculosis in immigrants in a low-incidence country.

Immigration from areas of high incidence is thought to have fueled the resurgence of tuberculosis (TB) in areas of low incidence. To reduce the risk of disease in low-incidence areas, the main countermeasure has been the screening of immigrants on arrival. This measure is based on the assumption of a prompt decline in the incidence of TB in immigrants during their first few years of residence in a country with low overall incidence. We have documented that this assumption is not true for 619 Somali immigrants reported in Denmark as having TB. The annual incidence of TB declined only gradually during the first 7 years of residence, from an initial 2,000 per 100,000 to 700 per 100,000. The decline was described by an exponential function with a half-time of 5.7 (95% confidence interval 4.0 to 9.7) years. This finding seriously challenges the adequacy of the customary practice of screening solely on arrival.

Bacillarity at autopsy in pulmonary tuberculosis. Mycobacterium tuberculosis is often disseminated.

The aim of this investigation was to quantify dissemination of Mycobacterium tuberculosis infection in patients with pulmonary tuberculosis and to show the pattern of eradication during treatment. The study is based on 98 out of the 113 patients with pulmonary tuberculosis who died during their admission to hospital in the Municipality of Copenhagen from 1963 to 1971. These patients had cultures for M. tuberculosis performed from different organs at autopsy: 78% treated <=100 days had dissemination of bacteria, cultured with decreasing frequency in the lungs, spleen, liver, and kidneys, respectively. In comparison, 23% treated >100 days had dissemination of bacteria, among which 50% occurred in patients with records of poor treatment compliance, 14% in patients with good treatment compliance. 81% of all patients had at least one chest x-ray judged to be without a miliary pattern. This study emphasizes that M. tuberculosis is often disseminated to organs other than the lungs in severe pulmonary tuberculosis. Eradication of bacteria in these organs can take several months. This observation adds to our understanding of the natural history of tuberculosis: M. tuberculosis is a resilient organism that can adapt to a wide variety of environmental conditions.