Impact of immigration on the molecular epidemiology of Mycobacterium tuberculosis in a low-incidence country

Patterns of antituberculous drug resistance in Eastern Saudi Arabia: a 7-year surveillance study from 1/2003 to 6/2010

OBJECTIVE

To examine the patterns of antituberculous drug resistance of Mycobacterium tuberculosis in patients with pulmonary and extra-pulmonary tuberculosis in the Eastern province of the Kingdom of Saudi Arabia.

METHODS

This is a retrospective study of antibiotic susceptibility of 1681 non-repetitive M. tuberculosis isolates from 1/2003 to 6/2010.

RESULTS

Of the total patients, 41% (n=687) were Saudis and 59% (n=994) were non-Saudis. The pulmonary and extra-pulmonary specimens constituted 68% (n=1148) and 32% (n=533), respectively. The incidence of resistance was 15.5% to one or more of anti-tuberculosis drugs. The resistance rates to first-line drugs were as follows: streptomycin (10.4%), INH (9.8%), rifampicin (1.5%) and ethambutol (1.0%). Multi-drug resistant tuberculosis was present in 1.4% (n=24) of the sample.

CONCLUSION

INH resistance in this study was relatively high, whereas the rate of MDR-TB was low. A rate of MDR-TB observed in this study was 1.4%. Thus, an empiric four-drug therapy is required to treat patients with tuberculosis in this area of Saudi Arabia.

Mycobacterium tuberculosis transmission in a country with low tuberculosis incidence: role of immigration and HIV infection

Immigrants from high-burden countries and HIV-coinfected individuals are risk groups for tuberculosis (TB) in countries with low TB incidence. Therefore, we studied their role in transmission of Mycobacterium tuberculosis in Switzerland. We included all TB patients from the Swiss HIV Cohort and a sample of patients from the national TB registry. We identified molecular clusters by spoligotyping and mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) analysis and used weighted logistic regression adjusted for age and sex to identify risk factors for clustering, taking sampling proportions into account. In total, we analyzed 520 TB cases diagnosed between 2000 and 2008; 401 were foreign born, and 113 were HIV coinfected. The Euro-American M. tuberculosis lineage dominated throughout the study period (378 strains; 72.7%), with no evidence for another lineage, such as the Beijing genotype, emerging. We identified 35 molecular clusters with 90 patients, indicating recent transmission; 31 clusters involved foreign-born patients, and 15 involved HIV-infected patients. Birth origin was not associated with clustering (adjusted odds ratio [aOR], 1.58; 95% confidence interval [CI], 0.73 to 3.43; P = 0.25, comparing Swiss-born with foreign-born patients), but clustering was reduced in HIV-infected patients (aOR, 0.49; 95% CI, 0.26 to 0.93; P = 0.030). Cavitary disease, male sex, and younger age were all associated with molecular clustering. In conclusion, most TB patients in Switzerland were foreign born, but transmission of M. tuberculosis was not more common among immigrants and was reduced in HIV-infected patients followed up in the national HIV cohort study. Continued access to health services and clinical follow-up will be essential to control TB in this population.

[Influence of immigration on tuberculosis transmission patterns in Castellón, Spain (2004-2007)]

BACKGROUND

This study aimed to identify tuberculosis transmission patterns in Castellón in a period of major demographic changes.

METHODS

A prospective study of patients with positive culture in the province of Castellon over a 4-year period (2004-2007) was carried out. Cases were described by year and nationality and were compared with those reported to the Department of Public Health. We studied the population with available molecular patterns, identified through restriction fragment length polymorphism (RFLP) and analyzed the variables from patient clusters, based on data collected in surveys of the Department of Health and the Laboratory Management Program.

RESULTS

According to data from the Department of Public Health, the overall rate of tuberculosis per 100,000 inhabitants in the province of Castellón was 15.7 in 2004, 19.9 in 2005, 18.2 in 2006 and 17.5 in 2007. In our laboratory, strains were identified from 301 patients, representing 77% (301/390) of reported cases and 94% (301/321) of reported cases with a positive culture. The percentage of tuberculosis among foreigners increased with age, exceeding 50% in 2007. Molecular studies were available in 95% of patients (286); 58% were Spanish and 42% were foreigners, of whom 54% were Romanians. The cluster percentage was 40%, with 30% of mixed clusters. According to conventional contact studies, 85% of patients in clusters had been considered isolated cases.

CONCLUSIONS

The increased rate of tuberculosis in Castellón was mainly due to the increasing number of cases among foreigners, mostly Romanians. The availability of molecular studies in all patients with a positive culture allowed us to analyze how and where tuberculosis is transmitted in our province. Forty percent of the patients were grouped into clusters; of these, mixed clusters accounted for one third, indicating the high integration of immigrants in our area.

Influence of sampling on clustering and associations with risk factors in the molecular epidemiology of tuberculosis

Molecular epidemiologic studies may use genotypic clustering of isolates as an indicator of recent transmission. It has been shown that missing cases lead to underestimating clustering, and modelling studies suggested that they may also lead to underestimating odds ratios for clustering. Using a national, comprehensive database from the Netherlands covering 15 years between 1993 and 2007 and including over 12,000 patients and their isolates, the authors determined the effects of sampling at random, in time, and by geographic area. As expected, sampling reduced the observed clustering percentages. However, sampling did not reduce the observed odds ratios for clustering. The main explanations for this discrepancy with model outcomes were that a substantial proportion of clustered cases were found in large clusters and that risk factors for clustering tended to be-among clustered cases-also risk factors for large clusters. The authors conclude that, in settings where risk factors for clustering may be interpreted as risk factors for recent transmission, these risk factors are also associated with larger cluster sizes. As a result, odds ratios would show limited sampling bias.

Genotyping of Mycobacterium tuberculosis: application in epidemiologic studies

Genotyping is used to track specific isolates of Mycobacterium tuberculosis in a community. It has been successfully used in epidemiologic research (termed 'molecular epidemiology') to study the transmission dynamics of TB. In this article, we review the genetic markers used in molecular epidemiologic studies including the use of whole-genome sequencing technology. We also review the public health application of molecular epidemiologic tools.

Childhood tuberculosis: an emerging and previously neglected problem

Although awareness is growing, childhood tuberculosis (TB) remains a neglected disease in many resource-limited settings. In part this reflects operational difficulties, lack of visibility in official reports, as well as perceptions that children tend to develop mild disease, contribute little to disease transmission, and do not affect epidemic control. At an international level there is greater appreciation that children contribute significantly to the global TB disease burden and suffer severe TB-related morbidity and mortality, particularly in TB-endemic areas, where the disease often remains undiagnosed. However, this is not always the case at the national or local level and there remains an urgent need for feasible and implementable policies to guide clinical practice. Pediatric TB can be regarded as an emerging epidemic in areas where the adult epidemic remains out of control and Mycobacterium tuberculosis transmission is ongoing. This article reviews important concepts, challenges, and management principles related to childhood TB; it also summarizes the main priorities for future research.

The role of entry screening in case finding of tuberculosis among asylum seekers in Norway

Background

Most new cases of active tuberculosis in Norway are presently caused by imported strains and not transmission within the country. Screening for tuberculosis with a Mantoux test of everybody and a chest X-ray of those above 15 years of age is compulsory on arrival for asylum seekers.

We aimed to assess the effectiveness of entry screening of a cohort of asylum seekers. Cases detected by screening were compared with cases detected later. Further we have characterized cases with active tuberculosis.

Methods

All asylum seekers who arrived at the National Reception Centre between January 2005 - June 2006 with an abnormal chest X-ray or a Mantoux test ≥ 6 mm were included in the study and followed through the health care system. They were matched with the National Tuberculosis Register by the end of May 2008.

Cases reported within two months after arrival were defined as being detected by screening.

Results

Of 4643 eligible asylum seekers, 2237 were included in the study. Altogether 2077 persons had a Mantoux ≥ 6 mm and 314 had an abnormal chest X-ray. Of 28 cases with tuberculosis, 15 were detected by screening, and 13 at 4-27 months after arrival. Abnormal X-rays on arrival were more prevalent among those detected by screening. Female gender and Somalian origin increased the risk for active TB.

Conclusion

In spite of an imperfect follow-up of screening results, a reasonable number of TB cases was identified by the programme, with a predominance of pulmonary TB.

The emergence of extensively drug-resistant tuberculosis: a global health crisis requiring new interventions: part I: the origins and nature of the problem

Surveillance studies and outbreak investigations indicate that an extensively drug-resistant (XDR) form of tuberculosis (TB) is increasing in prevalence worldwide. In outbreak settings among HIV-infected, there is a high-case fatality rate. Better outcomes occur in HIV-uninfected, particularly if drug susceptibility test (DST) results are available rapidly to allow tailoring of drug therapy. This review will be presented in two segments. The first characterizes the problem posed by XDR-TB, addressing the epidemiology and evolution of XDR-TB and treatment outcomes. The second reviews technologic advances that may contribute to the solution, new diagnostics, and advances in understanding drug resistance and in the development of new drugs.

Molecular epidemiology of Mycobacterium tuberculosis clinical isolates in Southwest Ireland

Tuberculosis has had significant effects on Ireland over the past two centuries, causing persistently higher morbidity and mortality than in neighbouring countries until the last decade. This study describes the results of genotyping and drug susceptibility testing of 171 strains of Mycobacterium tuberculosis complex isolated between January 2004 and December 2006 in a region of Ireland centred on the city of Cork. Spoligotype comparisons were made with the SpolDB4 database and clustered 130 strains in 23 groups, forty-one strains showed unique Spoligotyping patterns. The commonest spoligotypes detected were ST0137 (X2) (16.9%), and ST0351 (15.8%) ('U' clade). The major spoligotype clades were X (26.2%), U (19.3%), T (15.2%), Beijing (5.9%), Haarlem (4.7%), LAM (4.1%), BOVIS (1.75%), with 12.9% unassigned strains. A 24-locus VNTR genotyping produced 15 clusters containing 49 isolates, with high discrimination index (HGDI>0.99). A combination of Spoligotyping and VNTR reduced the number of clustered isolates to 47 in 15 clusters (27.5%). This study identified ST351 as common among Irish nationals, and found a low rate of drug resistance with little evidence of transmission of drug resistant strains. Strain clustering was significantly associated with age under 55 years and Irish nationality. Only strains of Euro-American lineage formed clusters. Molecular typing did not completely coincide with the results of contact investigations.

Genetic diversity of Mycobacterium tuberculosis Complex in Jos, Nigeria

Background

Nigeria has a high tuberculosis incidence, and genotyping studies of Mycobacterium tuberculosis Complex (MTC) in the country are necessary in order to improve our understanding of the epidemic.

Methods

Isolates of MTC were isolated from cases of pulmonary tuberculosis in Jos, North Central region of Nigeria during 2006-2008. Drug susceptibility test (DST) was performed on 77 of 111 isolates by proportion method on Lowenstein Jensen (LJ) slope while genotyping of mycobacterial DNA was performed by spoligotyping. The SpolDB4 database and the model-based program 'spotclust' were used to assign isolates to families, subfamilies and variants.

Results

A total of 111 pulmonary isolates from consecutive tuberculosis patients in the city of Jos, Plateau State, Nigeria were spoligotyped. A total of 84 (76%) of the isolates belonged to the Latin American Mediterranean (LAM) family. Of these, 78 isolates were assigned to the LAM10 lineage. Among these, 66 exhibited identical spoligopatterns. Drug susceptibility profiles obtained were not consistently associated with any spoligopattern.

Conclusions

The dominance of few M. tuberculosis lineages suggests either a high rate of transmission, frequent import of closely related strains, or a highly conserved genotype. It remains to be confirmed whether the predominance of identical LAM10 represent an outbreak.

Spoligotyping was useful to gain an overall understanding of the local TB epidemic. This study demonstrated that the incidence of TB in Jos, Nigeria may be caused by a few successful M. tuberculosis families, dominated by the LAM10 family.

Undocumented migrants in Switzerland: geographical origin versus legal status as risk factor for tuberculosis

Undocumented migrants, meaning migrants without a legal residency permit, come to Geneva from countries with high tuberculosis (TB) incidence. We estimate here whether being undocumented is a determinant of TB, independently of origin. Cross-sectional study including undocumented migrants in a TB screening program in 2002; results were compared to 12,904 age and frequency matched participants in a general TB screening program conducted at various workplaces in Geneva, Switzerland from 1992 to 2002. A total of 206 undocumented migrants (36% male, 64% female, mean age 37.8 years (SD 11.8), 82.5% from Latin America) participated in the TB screening program. Compared to legal residents, undocumented migrants had an adjusted OR for TB-related fibrotic signs of 1.7 (95% CI 0.8;3.7). The OR of TB-related fibrotic signs for Latin American (vs. other) origin was 2.7 (95% CI 1.6;4.7) among legal residents and 5.5 (95% CI 2.8;10.8) among undocumented migrants. Chest X-ray screening identified a higher proportion of TB-related fibrotic signs among Latin Americans, independently of their residency status.

Clinical presentation, demographics and outcome of tuberculosis (TB) in a low incidence area: a 4-year study in Geneva, Switzerland

Background

The incidence of tuberculosis (TB) in developed countries has decreased since the 1990s, reflecting worldwide efforts to identify and treat TB according to WHO recommendations. However TB remains an important public health problem in industrialized countries with a high proportion of cases occurring among subjects originating from high prevalence countries. The aim of this study was to describe clinical and social characteristics of patients with TB and their outcome in a low incidence area with a high immigration rate.

Methods

Four-year retrospective study based on a computerized database and subsequent review of medical records of all patients with TB followed at the outpatient section of the Division of Pulmonary Diseases, Geneva University Hospital, Switzerland.

Results

252 patients (84% foreigners, 25% asylum seekers) aged 38 ± 19 yrs were studied (11% co-infected with HIV). TB was intrapulmonary (TBP) in 158 cases (63%), extrapulmonary (TBE) in 137 (54%), and both in 43 cases (17%). TBP was smear (S)+/culture (C)+ in 59%, S-/C+ in 37%, S-/C- in 4%. Smoking was significantly associated with cavitary disease.

Time from onset of symptoms to diagnosis was 2.1 ± 3.1 months. Initially, 10% were asymptomatic; 35% had no general symptoms. Despite systematic sputum analysis (induced or spontaneous), TBP was confirmed only by bronchoscopy in 38 subjects (24% of TBP). Side effects requiring changes in treatment occurred in 38 cases (11%).

Treatment was completed in 210 (83%) patients. In 42 cases, follow up was unsuccessful; causes were: failure (n = 2; 0.8%), defaulters (n = 8; 3%), transfer out (n = 28; 11%) and death (n = 4; 1.6%). Relapse rate was 0.24 per 100 patient-years. Considering S+ TBP only, success rate was 87%.

Conclusion

TB in our area is predominantly a disease of young foreign-born subjects. Smoking appears as a possible risk factor for cavitary TBP. Time to diagnosis remains long. Compliance to treatment is satisfactory. Success rate for S+ TBP is within WHO objectives.

Transmission dynamics of pulmonary tuberculosis between autochthonous and immigrant sub-populations

Background

The overall incidence of tuberculosis (TB) in Western Europe has been declining since the 19^th Century. However, immigrant sub-groups from high-prevalence countries are slowing down this trend. The aim of this study was to describe how immigration influences TB transmission in Germany. For that we prospectively investigated the dynamics of TB transmission between TB high-prevalence immigrant and TB low-prevalence local populations with molecular epidemiological methods and conventional contact investigations. Besides, we assessed transmission in relation to social mixing using an innovative tool that measures the integration of immigrants into the local social environment.

Methods

A prospective study of confirmed culture positive cases of pulmonary TB and their contacts was carried out in a German federal state from 2003 to 2005. Data for the study included: 1) case data routinely collected by the local public health staff and transmitted to the state health office and the national surveillance centre, 2) a study questionnaire designed to capture social interactions of relevance for TB transmission and 3) molecular genotyping data (IS6110 DNA fingerprint and spoligotyping). The proportion of German cases caused by foreign-born cases, and vice versa, was estimated and an integration index was computed using a selected set of questions from the study questionnaire.

Results

A total of 749 cases of culture-positive pulmonary tuberculosis voluntarily enrolled in the study, representing 57.8% of all registered cases diagnosed over the study period. Data that included study questionnaire and DNA fingerprinting were available for 41% (n = 308) of the study participants. Forty-seven clusters, defined as a least two cases infected by the same TB strains, were identified by molecular methods and included 132 (17%) of the study participants. Epidemiological links were identified for 28% of the clusters by conventional epidemiological data. In mixed clusters, defined as clusters including German and foreign-born individuals, the probability of cases to be caused by foreign-born cases was estimated at 18.3%. We observed a trend to mixed clusters with increasing time spent by immigrants in the host country. This group also presented comparatively higher integration indexes than immigrants in immigrant-only clusters.

Conclusion

Our results confirm the findings of other studies that there is no significant TB transmission from TB high-prevalence immigrant to TB low-prevalence autochthonous population. This may be explained by the good performance of tuberculosis screening programmes for certain groups arriving in Germany from high- prevalence countries, by a low degree of mixing of immigrants with the local population or by a combination of both.

Tuberculosis cluster in an immigrant community: case identification issues and a transcultural perspective

OBJECTIVES

In a low incidence area for tuberculosis (TB), a computerized database identified an unusually high proportion of patients coming from one single country between 2004 and 2006. To determine whether they constituted a cluster, whether clustering was due to recent transmission, and to understand what undermined the efficacy of the contact tracing procedure, we conducted a retrospective study of all patients with TB from this country.

METHODS

Mycobacterium tuberculosis isolates of 15 TB cases originating from the same country over a 2(1/2) year period were analysed by restriction fragment length polymorphism (RFLP) and/or Rep-PCR. To identify links between patients, we revisited the social worker's files, cross-matched contacts' databases, and performed internet searches. A cultural evaluation was conducted by an anthropologist and an expert physician, through patient and community key informant interviews and a literature review.

RESULTS

Genotyping confirmed that 11 of 15 patients had identical isolates. Additional data revealed an unsuspected complex network of social links between 9 of these 11 patients. The transcultural evaluation pointed out the major obstacles to efficient contact tracing, such as importance of social stigma related to TB, differences in communication style and health beliefs, and linguistic barriers.

CONCLUSION

The combined finding of identical genotypes and important social links between patients confirmed the suspicion of a TB cluster due to recent transmission. The cultural evaluation helped to explain the difficulties encountered during the contact tracing procedure, and offered strategies to improve its efficacy despite the magnitude of the social stigma attached to TB in this community.

Prospective universal application of mycobacterial interspersed repetitive-unit-variable-number tandem-repeat genotyping to characterize Mycobacterium tuberculosis isolates for fast identification of clustered and orphan cases

The use of molecular tools for genotyping Mycobacterium tuberculosis isolates in epidemiological surveys in order to identify clustered and orphan strains requires faster response times than those offered by the reference method, IS6110 restriction fragment length polymorphism (RFLP) genotyping. A method based on PCR, the mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) genotyping technique, is an option for fast fingerprinting of M. tuberculosis, although precise evaluations of correlation between MIRU-VNTR and RFLP findings in population-based studies in different contexts are required before the methods are switched. In this study, we evaluated MIRU-VNTR genotyping (with a set of 15 loci [MIRU-15]) in parallel to RFLP genotyping in a 39-month universal population-based study in a challenging setting with a high proportion of immigrants. For 81.9% (281/343) of the M. tuberculosis isolates, both RFLP and MIRU-VNTR types were obtained. The percentages of clustered cases were 39.9% (112/281) and 43.1% (121/281) for RFLP and MIRU-15 analyses, and the numbers of clusters identified were 42 and 45, respectively. For 85.4% of the cases, the RFLP and MIRU-15 results were concordant, identifying the same cases as clustered and orphan (kappa, 0.7). However, for the remaining 14.6% of the cases, discrepancies were observed: 16 of the cases clustered by RFLP analysis were identified as orphan by MIRU-15 analysis, and 25 cases identified as orphan by RFLP analysis were clustered by MIRU-15 analysis. When discrepant cases showing subtle genotypic differences were tolerated, the discrepancies fell from 14.6% to 8.6%. Epidemiological links were found for 83.8% of the cases clustered by both RFLP and MIRU-15 analyses, whereas for the cases clustered by RFLP or MIRU-VNTR analysis alone, links were identified for only 30.8% or 38.9% of the cases, respectively. The latter group of cases mainly comprised isolates that could also have been clustered, if subtle genotypic differences had been tolerated. MIRU-15 genotyping seems to be a good alternative to RFLP genotyping for real-time interventional schemes. The correlation between MIRU-15 and IS6110 RFLP findings was reasonable, although some uncertainties as to the assignation of clusters by MIRU-15 analysis were identified.

Ethical considerations about reporting research results with potential for further stigmatization of undocumented immigrants

A broad spectrum of infectious diseases is studied in vulnerable populations. However, ethical considerations of reporting research results that could increase stigmatization of socially marginalized and vulnerable populations are not often discussed in the medical literature, particularly not in the context of transmissible diseases. This article addresses ethical considerations that arose when one of us (J.M.A.) recently published the results of a study in Clinical Infectious Diseases that imply that undocumented persons are more likely to transmit tuberculosis than are documented foreign-born persons or persons born in the United States. These study results have the potential to further fuel the often fierce debate regarding undocumented immigrants in the United States. To our knowledge, such ethical considerations have not been discussed previously in the medical literature.

Screening for latent tuberculosis infection among undocumented immigrants in Swiss healthcare centres; a descriptive exploratory study

Background

Migration is one of the major causes of tuberculosis in developed countries. Undocumented patients are usually not screened at the border and are not covered by a health insurance increasing their risk of developing the disease unnoticed. Urban health centres could help identify this population at risk. The objective of this study is to assess the prevalence of latent tuberculosis infection (LTBI) and adherence to preventive treatment in a population of undocumented immigrant patients.

Methods

All consecutive undocumented patients that visited two urban healthcare centres for vulnerable populations in Lausanne, Switzerland for the first time were offered tuberculosis screening with an interferon-γ assay. Preventive treatment was offered if indicated. Adherence to treatment was evaluated monthly over a nine month period.

Results

Of the 161 participants, 131 (81.4%) agreed to screening and 125 had complete examinations. Twenty-four of the 125 patients (19.2%; CI95% 12.7;27.2) had positive interferon-γ assay results, two of which had active tuberculosis. Only five patients with LTBI completed full preventive treatments. Five others initiated the treatment but did not follow through.

Conclusion

Screening for tuberculosis infection in this hard-to-reach population is feasible in dedicated urban clinics, and the prevalence of LTBI is high in this vulnerable population. However, the low adherence to treatment is an important public health concern, and new strategies are needed to address this problem.

Differences in clinical presentation among persons with pulmonary tuberculosis: a comparison of documented and undocumented foreign-born versus US-born persons

BACKGROUND

Most cases of tuberculosis (TB) in the United States are diagnosed in foreign-born persons, and undocumented foreign-born persons may face particular barriers to timely access to health care services. This study investigates whether differences in clinical presentations among persons with pulmonary TB are associated with foreign birth or documentation status.

METHODS

In this cross-sectional study, we reviewed the medical records of patients who had received a diagnosis of microbiologically proven pulmonary TB at a New York City public hospital during the period April 1999 through March 2005. Three groups of patients with pulmonary TB (US-born persons, foreign-born persons with documents, and undocumented, foreign-born persons) were defined and compared at presentation. Odds ratios (ORs) for a symptom duration >or=8 weeks before hospital admission for each group were estimated using logistic regression.

RESULTS

Among 194 subjects with newly diagnosed pulmonary TB, 61 (31%) were US born, 62 (32%) were documented foreign-born persons, and 71 (37%) were undocumented foreign-born persons. Undocumented foreign-born persons presented with significantly higher frequencies of cough (P = .020) and hemoptysis P = .012 and had a significantly longer median duration of symptoms, compared with US-born persons (8 vs. 4 weeks; P = .023). No statistically significant differences between documented foreign-born and US-born persons were observed. Multivariate analysis revealed that undocumented status (compared with being US born; adjusted OR, 4.1; 95% confidence interval, 1.7-10.2; P = .0002) and being unemployed (adjusted OR, 2.2; 95% CI, 1.1-4.5; P = .023) were independently associated with a prolonged symptom duration (i.e., >or=8 weeks).

CONCLUSIONS

Undocumented status was associated with an increased frequency of cough and hemoptysis and a longer duration of symptoms before medical evaluation for pulmonary TB. Whether reducing barriers to health services for undocumented foreign-born persons could enhance TB control deserves additional study.

School based screening for tuberculosis infection in Norway: comparison of positive tuberculin skin test with interferon-gamma release assay

Background

In Norway, screening for tuberculosis infection by tuberculin skin test (TST) has been offered for several decades to all children in 9th grade of school, prior to BCG-vaccination. The incidence of tuberculosis in Norway is low and infection with M. tuberculosis is considered rare. QuantiFERON^®TB Gold (QFT) is a new and specific blood test for tuberculosis infection. So far, there have been few reports of QFT used in screening of predominantly unexposed, healthy, TST-positive children, including first and second generation immigrants. In order to evaluate the current TST screening and BCG-vaccination programme we aimed to (1) measure the prevalence of QFT positivity among TST positive children identified in the school based screening, and (2) measure the association between demographic and clinical risk factors for tuberculosis infection and QFT positivity.

Methods

This cross-sectional multi-centre study was conducted during the school year 2005–6 and the TST positive children were recruited from seven public hospitals covering rural and urban areas in Norway. Participation included a QFT test and a questionnaire regarding demographic and clinical risk factors for latent infection. All positive QFT results were confirmed by re-analysis of the same plasma sample. If the confirmatory test was negative the result was reported as non-conclusive and the participant was offered a new test.

Results

Among 511 TST positive children only 9% (44) had a confirmed positive QFT result. QFT positivity was associated with larger TST induration, origin outside Western countries and known exposure to tuberculosis. Most children (79%) had TST reactions in the range of 6–14 mm; 5% of these were QFT positive. Discrepant results between the tests were common even for TST reactions above 15 mm, as only 22 % had a positive QFT.

Conclusion

The results support the assumption that factors other than tuberculosis infection are widely contributing to positive TST results in this group and indicate the improved specificity of QFT for latent tuberculosis. Our study suggests a very low prevalence of latent tuberculosis infection among 9th grade school children in Norway. The result will inform the discussion in Norway of the usefulness of the current TST screening and BCG-policy.

Discordance between mycobacterial interspersed repetitive-unit-variable-number tandem-repeat typing and IS6110 restriction fragment length polymorphism genotyping for analysis of Mycobacterium tuberculosis Beijing strains in a setting of high incidence of tuberculosis

IS6110 restriction fragment length polymorphism (RFLP) genotyping is the most widely used genotyping method to study the epidemiology of Mycobacterium tuberculosis. However, due to the complexity of the IS6110 RFLP genotyping technique, and the interpretation of RFLP data, mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) genotyping has been proposed as the new genotyping standard. This study aimed to determine the discriminatory power of different MIRU-VNTR locus combinations relative to IS6110 RFLP genotyping, using a collection of Beijing genotype M. tuberculosis strains with a well-established phylogenetic history. Clustering, diversity index, clustering concordance, concordance among unique genotypes, and divergent and convergent evolution were calculated for seven combinations of 27 different MIRU-VNTR loci and compared to IS6110 RFLP results. Our results confirmed previous findings that MIRU-VNTR genotyping can be used to estimate the extent of recent or ongoing transmission. However, molecular epidemiological linking of cases varied significantly depending on the genotyping method used. We conclude that IS6110 RFLP and MIRU-VNTR loci evolve independently and at different rates, which leads to discordance between transmission chains predicted by the respective genotyping methods. Concordance between the two genotyping methods could be improved by the inclusion of genetic distance (GD) into the clustering formulae for some of the MIRU-VNTR loci combinations. In summary, our findings differ from previous reports, which may be explained by the fact that in settings of low tuberculosis incidence, the genetic distance between epidemiologically unrelated isolates was sufficient to define a strain using either marker, whereas in settings of high incidence, continuous evolution and persistence of strains revealed the weaknesses inherent to these markers.

Screening for tuberculosis infection among newly arrived asylum seekers: comparison of QuantiFERONTB Gold with tuberculin skin test

Background

QuantiFERON^®TB Gold (QFT) is a promising blood test for tuberculosis infection but with few data so far from immigrant screening. The aim of this study was to compare results of QFT and tuberculin skin test (TST) among newly arrived asylum seekers in Norway and to assess the role of QFT in routine diagnostic screening for latent tuberculosis infection.

Methods

The 1000 asylum seekers (age ≥ 18 years) enrolled in the study were voluntarily recruited from 2813 consecutive asylum seekers arriving at the national reception centre from September 2005 to June 2006. Participation included a QFT test and a questionnaire in addition to the mandatory TST and chest X-ray.

Results

Among 912 asylum seekers with valid test results, 29% (264) had a positive QFT test whereas 50% (460) tested positive with TST (indurations ≥ 6 mm), indicating a high proportion of latent infection within this group. Among the TST positive participants 50% were QFT negative, whereas 7% of the TST negative participants were QFT positive. There was a significant association between increase in size of TST result and the likelihood of being QFT positive. Agreement between the tests was 71–79% depending on the chosen TST cut-off and it was higher for non-vaccinated individuals.

Conclusion

By using QFT in routine screening, further follow-up could be avoided in 43% of the asylum seekers who would have been referred if based only on a positive TST (≥ 6 mm). The proportion of individuals referred will be the same whether QFT replaces TST or is used as a supplement to confirm a positive TST, but the number tested will vary greatly. All three screening approaches would identify the same proportion (88–89%) of asylum seekers with a positive QFT and/or a TST ≥ 15 mm, but different groups will be missed.

Molecular epidemiology of drug-resistant tuberculosis in Sweden

Drug-resistant tuberculosis (TB), including the more severe forms of multidrug- and extensively drug-resistant forms, is an increasing public health concern globally. In Sweden the majority of patients with TB are immigrants from countries with a high incidence of TB including the drug-resistant forms. In this study, the spread of resistant TB in Sweden was investigated by molecular fingerprinting. Isolates resistant to at least one of the drugs, isoniazid, rifampicin, ethambutol or streptomycin, from 400 patients collected between 1994 and 2005, were studied by restriction fragment length polymorphism (RFLP) and by spoligotyping. Thirty-five clusters of patients infected with strains with identical RFLP and spoligotyping patterns (2-96 patients per cluster), comprising a total of 203 patients, were found. One large outbreak of isoniazid resistant tuberculosis was identified, involving 96 patients, mainly from the Horn of Africa. To identify chains of transmission, molecular epidemiological characterization of TB isolates should, if possible, be performed on isolates from all new TB patients.