Chest ACCP Education Calendar
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Guest Access | Sign In via User Name/Password
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Marras, T. K.
Right arrow Articles by Yang, J. W.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Marras, T. K.
Right arrow Articles by Yang, J. W.
(Chest. 2003;124:915-921.)
© 2003 American College of Chest Physicians

Tuberculosis Among Tibetan Refugee Claimants in Toronto*

1998 to 2000

Theodore K. Marras, MD; Jean Wilson, BScN, MHSc; Elaine E. L. Wang, MD; Monica Avendano, MD, FCCP and Jae Won Yang, MD, FCCP

* From the Departments of Medicine (Drs. Marras, Avendano, and Yang) and Pediatrics (Dr. Wang), University of Toronto; and St. Michael’s Hospital Tuberculosis Program (Ms. Wilson), Toronto, Ontario, Canada.

Correspondence to: Theodore K. Marras, MD, The Asthma Centre, Toronto Western Hospital, 4th Floor Edith Cavell, 399 Bathurst St, Toronto, ON, M5T 2S8, Canada; e-mail: ted.marras{at}utoronto.ca


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Background and objectives: Between 1998 and 2000, approximately 525 Tibetan people previously living in the United States claimed refugee status in Canada, many of whom were referred to our centers for completion of tuberculosis (TB) screening. We reviewed TB-related outcomes in this cohort, to compare our experience with previously published work, and to assess follow-up after a stay in a low-incidence region.

Methods: We performed a retrospective study of all patients of Tibetan origin assessed at our centers (St. Michael’s Hospital and West Park Healthcare Centre, both in Toronto) for completion of TB screening, referred because of abnormal chest radiographic findings or positive tuberculin skin test (TST) result. We compared rates of active and drug-resistant TB in our cohort with local and national rates, as well as those previously published in similar groups.

Results: One hundred eighty-nine individuals were referred to us for assessment, and 181 records were available for review. The mean duration of stay in Canada prior to presentation was 2.6 months, after having spent a mean of 11 months in the United States. Thirty-two percent of patients gave a history of previous TB, and 97% were TST positive. Culture-positive TB was diagnosed in 24 patients (13%, 4,571 per 100,000), 12 patients had at least one drug resistance (50% of cases), and 4 patients were resistant to at least isoniazid and rifampin (multidrug resistant, 17% of cases).

Interpretation: People from highly TB endemic areas retain a very high risk of active TB and drug resistance, despite an intervening period in a low-prevalence country. It is important to maintain a high degree of suspicion for TB in all people from high-incidence areas. Treatment of all cases of latent TB infection or ongoing medical surveillance is likely justified in this population.

Key Words: emigration and immigration • refugees • tuberculin test • tuberculosis, multidrug-resistant


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
The global prevalence of tuberculosis (TB) infection is estimated to be 32%, with approximately 8 million new symptomatic cases and 1.9 million TB-related deaths annually and a rising incidence of drug-resistant TB (DRTB).1 Ten percent of new cases of active TB are resistant to at least one first-line agent, and 1% have multidrug-resistant TB (MDRTB) [resistant to at least isoniazid and rifampin].2 The annual incidence of new cases varies from > 250 cases per 100,000 in some heavy-burden nations, to < 10 per 100,000 in low-burden countries (including Canada and the United States).1 Drug-resistance rates are highest in places such as Russia, where rates of DRTB and MDRTB are 30 to 40% and 10%, respectively. Canadian figures correspond to the global median, 10% and 1%, respectively,2 with slowly increasing levels over the past decade in the province of Ontario.3

As the incidence of TB in Canada dropped in the second half of the 20th century, the proportion of cases diagnosed in foreign-born individuals rose steadily, reaching nearly 60% by 19954 and 85% in Ontario.5 This reflects migration patterns from highly TB endemic countries. Current Canadian screening policy for refugee claimants in Canada requires the initiation of appropriate investigations for TB within 30 days of arrival if their claim was made outside of Canada, or within 60 days of their claim for applicants within Canada. This system could lead to delayed or incomplete screening.

Very high rates of active and MDRTB were reported in a group of Tibetans from India and Nepal who entered the United States in 1990.6 No publications on subsequent migration of this or similar groups have been reported. Between 1998 and 2000, a group of Tibetan people who had entered the United States as visitors entered Canada and claimed refugee status. Beginning in 1990, as part of a humanitarian effort, there was a resettlement of Tibetans from India and Nepal to the United States. Some Tibetans who initially came to the United States subsequently entered Canada and claimed refugee status. Members of our cohort sought refugee status in Canada after lengthy US stays as visitors, because they were no longer able to maintain their visitor status or otherwise extend their stay in the United States. Most initially settled in Toronto, and many had TB screening completed at our center. We sought to review TB-related outcomes in this cohort, to compare our experience with the findings of Truong et al,6 and to assess longer-term follow-up after a stay in a low-incidence region.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Patients were included for study if they were self-identified as Tibetan, entered Canada between 1998 and 2000, and were referred to St. Michael’s Hospital or West Park Healthcare Centre in Toronto. Referrals came from three sources: Canadian immigration officials, the City of Toronto Public Health Department (PHD), or community physicians. Canadian immigration-designated medical practitioners initially assessed all individuals clinically and with chest radiographs (CXRs). Reasons for referral for further assessment included a clinical suspicion of TB, a CXR abnormality consistent with TB, and a history of previous TB. Through discussions with local Canadian immigration designated medical practitioners, we surmised that the majority with an abnormal CXR finding were referred to us. In addition, between July and September 1999, the PHD initiated a campaign to identify and perform a tuberculin skin test (TST) on all recently arrived Tibetan refugees. Individuals with a positive TST result were referred to our centers. We therefore had the opportunity to assess a subgroup of recent Tibetan immigrants deemed to be at high risk for TB, based on an abnormal CXR findings or positive TST results.

Data were collected retrospectively from medical records at St. Michael’s Hospital, a referral center for TB cases in Toronto and West Park Healthcare Centre, housing the only inpatient service for complicated TB cases in Ontario. Both are University of Toronto-affiliated teaching hospitals. The St. Michael’s Hospital/West Park Healthcare Centre institutional research ethics board approved the study, and all work was in accordance with the Helsinki Declaration of 1975.7

Patients were assessed with a history, physical examination, CXR (reviewed by a pulmonary medicine physician and a radiologist), TST (positive result defined as a >= 10-mm induration 48 to 72 h after intradermal injection of 5 tuberculin units of purified protein derivative), and sputum smear and culture findings (in most patients). Individuals with suggestive symptoms or a CXR finding considered to be consistent with TB were investigated microbiologically, including flexible bronchoscopy if sputum could not be obtained. Latent TB infection (LTBI) was defined by a positive TST result and either a normal CXR finding or negative microbiologic investigations. Active TB was diagnosed when Mycobacterium tuberculosis was recovered (culture-positive TB) or negative culture findings with consistent clinical signs, symptoms, and/or radiographic abnormalities that improved after antituberculous therapy (culture-negative TB). Previous TB, currently inactive, was defined as a history of previous TB treatment, negative microbiologic investigations, and the lack of criteria for culture-negative TB. Individuals unavailable for follow-up before specimens could be sent for microbiologic studies were classified as unknown. Patients were treated in accordance with the contemporary edition of the Canadian standards for the treatment of TB,8 similar to the American Thoracic Society guidelines.9 10

Accurate figures on the number of Tibetan refugee claimants settling in our area were unavailable. In conjunction with the Ontario Ministry of Health and Long Term Care, members of the Toronto Tibetan community, and the PHD, we estimated that 525 people of Tibetan origin claimed refugee status during the study period. We used this figure as the denominator in rate calculations, and estimated that the true number fell within the plausible range of 450 to 600 people. We calculated confidence intervals using 450 as the sample size, which provides a greater calculated variance and wider and more conservative confidence intervals. Rates of active TB and drug resistance were compared with relevant previously published reports.1 5 To facilitate comparisons, we assumed that prevalence from our experience approximated incidence. We used the Yates-corrected {chi}2 and the Wilcoxon test to compare categoric and continuous variables, respectively. Analysis was performed using SAS version 8.0 (SAS Institute; Cary, NC).


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
An estimated 525 Tibetan people crossed the border into Ontario, Canada between 1998 and early 2001. One hundred eighty-nine individuals were referred for assessment, and records were available for review in 181 patients. The mean age was 29 years, and 123 (68%) were male. Fifty-eight patients (32%) gave a history of previous TB. Two patients each had received a diagnosis of active TB or LTBI in the United States and were still receiving treatment when they entered Canada. History of bacille Calmette-Guérin vaccination status was available in < 10% of patients. Eighty-seven patients (48%) were born in India, 54 patients (30%) were born in Tibet, and 38 patients (21%) were born in Nepal. Information regarding refugee camp residence was unavailable for most patients. New York City was the most common site of previous stay in the United States, with at least 116 of patients (64%) having spent a mean of 11 months there. Other sites of stay included Chicago, Detroit, Boston, and Minneapolis-St. Paul. The mean durations of stay in the United States and Canada prior to presentation were 11 months and 2.6 months, respectively. All individuals were refugee claimants in Canada.

Results of patient investigations are presented in Table 1 . CXR abnormalities included nodules in 96 patients (55 were calcified), fibrotic change in 76 patients, pleural thickening in 36 patients, volume loss in 20 patients, cavitation in 15 patients, airspace opacities in 14 patients, and pleural effusion in 2 patients (several patients had more than one abnormality). Nearly every patient tested had a positive TST result, and the mean induration was 20 mm. Of the 155 sputum and 34 bronchoscopy specimens obtained, culture-positive rates were 12% and 21%, respectively.


View this table:
[in this window]
[in a new window]

  		Table 1. Results of Patient Investigations*

 
The classification of patients is presented in Table 2 . LTBI was present in nearly one half of patients, previous TB (currently inactive) in one quarter of patients, and active TB in 17% of patients. The management and outcomes of patients with LTBI are presented in Table 3 . Patients who reported previous TB had received treatment a median of 12 years (range, 1 to 32 years) previously, with 43 of 45 patients (96%) treated outside of North America, primarily in India and Nepal.


View this table:
[in this window]
[in a new window]

  		Table 2. Patient Classification

 

View this table:
[in this window]
[in a new window]

  		Table 3. Management of Patients With LTBI*

 
The median age of patients with active TB was 27 years, compared with 29 years in others (p = 0.21). Of patients with active TB, only 5 of 31 patients (16%) gave a history of symptoms, with a median duration of 2 months (range, 1 to 12 months). All patients with active TB had an abnormal CXR finding (compared with 84 of 150 patients [56%] without active TB; p < 0.0001), and all were HIV negative. The average patient with active TB had spent 15 months in the United States and 3 months in Canada before our assessment. There was no statistically significant difference in time to assessment between those with and without active TB.

Of culture-confirmed cases, 12 patients were fully sensitive and 12 patients had DRTB. Four patients were resistant to streptomycin alone, one patient was resistant to isoniazid alone, two patients were resistant to isoniazid and streptomycin, one patient was resistant to isoniazid, ethambutol, streptomycin, and ethionamide, and four patients had MDRTB (including one patient with 10-drug resistance). Incidence of culture-confirmed TB and rates of drug resistance are presented in Table 4 , along with relevant previously published rates. Median duration of therapy for fully sensitive TB was 6 months (range, 6 to 12 months), and 30 months (range, 23 to 36 months) for MDRTB. All patients converted their sputum and were judged to have sustained clinical cures. Completion rates were 100% as work permits and landed status were otherwise withheld. There were no statistically significant associations between a history of previous TB and culture-positive TB, DRTB, or drug resistance among culture-proven cases.


View this table:
[in this window]
[in a new window]

  		Table 4. Rates of Active TB and Drug Resistance in Several Groups*

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Individuals of Tibetan origin entering Canada from the United States were found to have extremely high levels of active and DRTB. Two contributing factors help explain this alarming finding. These patients originated primarily from northern India, which has some of the highest rates of TB in the world, as well as high levels of drug resistance.1 Members of this cohort differ from other Canadian immigrants from northern India by their self-identification as Tibetan and their intervening stay in a low-incidence nation. We also believe that many of these people stayed in refugee camps in northern India, but these data are not available to us. Superimposed on this, recent migration and refugee status are recognized risk factors for the development of active TB.13 14 15 Truong and colleagues6 observed similarly high rates of active and DRTB in a group of Tibetans in Minnesota, and others16 17 18 have reported high rates of DRTB in populations from similarly endemic regions. Our work differs in that we assessed a large group of people after a mean of 11 months in a low-prevalence country, and demonstrated very high rates of active and DRTB at this later time. This finding underscores the high ongoing risk of disease, reported for up to 5 years after migration.6 19 TB must therefore always be considered in people who come from high-incidence regions, regardless of intervening stays in low-incidence areas. We considered members of this cohort with the same level of suspicion as Tibetan refugees coming directly from northern India and nearby areas. The particularly high rates observed by us and Truong et al,6 apparently unique to newcomers of Tibetan origin, also suggest that immigration authorities in both the United States and Canada should be aware of our findings to ensure members of this group receive appropriate screening and surveillance.

High rates of previous TB and inadequate treatment likely also contributed to the high DRTB rate. We were unable to demonstrate an association between a previous history of TB and DRTB, which could relate to an underreporting bias. Members of our cohort may have believed it was in their best interest to not report previous episodes of TB, for fear of jeopardizing success of pending refugee claims and the social stigma often attached to this disease.

It is very likely that a significant number of the cases of active TB we detected were present while the patients were still living in the United States. That these cases were not detected during US residence may be due to the fact that people entering the United States (or Canada) as visitors may not require screening for TB. This could present a tremendous public health problem. According to an estimate in a US Institute of Medicine report,20 members of the group of people who entered the United States as visitors in 1996 alone could contribute 2,000 new cases of TB during their stay. In Canada, visitors who have lived in a country with high rates of TB for at least 6 months of the past year and intend to stay in Canada for at least 6 months are required to undergo an immigration medical examination.21 This stipulation would not require screening of people, like members of our cohort, who maintain a high risk despite an intervening period in a low-incidence region. In both countries, screening is mandated for those seeking to adjust their status after arriving on temporary visas, but this does not address the initial and possibly highest risk period.

The time from entry into Canada and initiation of screening is concerning, given the very high rates of active TB and drug resistance we observed. The mean time to presentation was 2.6 months, regardless of CXR abnormality or the presence of active disease. This duration falls short of current Canadian screening recommendations, likely reflecting the challenges inherent in achieving timely radiographic and clinical evaluation in people in an unfamiliar environment. We thus support calls to improve the current screening system,22 and stress its limitations in assessing refugee claimants.

Our findings stress the importance of initial screening, especially in people originating from high-incidence regions and lend support to the Canadian refugee and immigration policy of CXR screening in those > 11 years old. All active cases were detected on initial screening after entry into Canada. As expected, we observed that CXR abnormalities demonstrate an extremely high sensitivity (100% in this series) in detecting active TB cases; however, this finding is likely biased, since the results of the CXR undoubtedly influenced whether or not further investigations were performed.

Given the high ongoing risk of disease in newcomers from high-prevalence countries, it must be stressed that initial screening is only the first component in the control of TB in high-risk newcomers. We feel that treating LTBI is important and, consistent with current guidelines, agree strongly that age > 35 years is not a general contraindication to therapy for LTBI.11 In addition, based on the very high rates of active TB we observed in our cohort, members of similar groups should likely be considered to have a high likelihood of recent infection, and treatment of LTBI should be considered more strongly and pursued more vigorously. Further, we strongly support recommendations regarding medical surveillance of high-risk people who are not treated for LTBI.11 Identification of people with LTBI currently rests on the use of TSTs. One might consider expanding the screening protocol to include universal TSTs. Decision analysis models in this area have yielded conflicting results, possibly due to differences in patient grouping (all immigrants as a whole vs subsets defined according to estimated risk of LTBI) or estimates of LTBI treatment completion rates.23 24 Khan et al23 found the detection and treatment of LTBI was cost-effective in immigrants to the United States from many developing nations. Schwartzman and Menzies24 modeled the use of TST screening in immigrants as not cost-effective, primarily reflecting use in low-risk patient groups and poor adherence to LTBI treatment regimens. Including TST in screening becomes more attractive if it is targeted toward high-risk groups and a high rate of LTBI treatment completion is achieved. Our relatively low rates of LTBI treatment and its completion are concerning. Of eligible patients with LTBI, 20% were unavailable for follow-up before treatment, and rates of completion were only 61%. Truong and colleagues6 reported treatment of LTBI in 58% of a similar cohort, compared with 43% in our series, but did not provide data on completion rates.

The definition of high-risk newcomers may not always be clear. The current Canadian recommendation regarding which visitors require TB screening are based on having lived in a country with high rates of TB for at least 6 months of the past year.21 We feel that this reflects an inadequate view in identifying high-risk people. When defining TB risk status according to regions of previous residence, we advocate a longer time horizon, possibly 5 years. This threshold may be a more useful one for practitioners assessing people for the presence of active TB, LTBI, and consideration regarding treatment of LTBI.

The choice of optimal regimen for treating LTBI in newcomers from areas with very high rates of DRTB is unknown. During the period when members of our cohort were being assessed, the prevalence of DRTB and MDRTB in this group were not yet clear to us, and we used the most commonly employed regimens for treating LTBI. If the 33% rate of resistance to isoniazid in active TB cases was representative of the prevalence of isoniazid resistance in the cohort as a whole, one would expect that isoniazid LTBI treatment would be effective in < 67%, given its imperfect effectiveness in optimal circumstances. Guidelines have been developed regarding the treatment of LTBI in patients exposed to patients with MDRTB and known resistance patterns,10 but there is little guidance available for treating patients who are at high risk for DRTB and MDRTB based on other risk factors. Given that the majority of patients with LTBI are likely infected with organisms that are sensitive to isoniazid (even in patients from areas where resistance to isoniazid is high) and the lack of data regarding the efficacy of regimens for treating LTBI in DRTB and MDRTB, we continue to recommend the use of standard regimens but would consider alternative regimens in exceptional circumstances, where we would also advocate systematic follow-up in an attempt to assess effectiveness. This recommendation is supported by Khan et al,23 who presented a cost-effectiveness analysis addressing this issue. The authors recommend isoniazid, rifampin, or rifampin plus pyrazinamide for treating LTBI in immigrants to the United States who originate from India and the neighboring nations. Further, the burden of organisms in LTBI is likely low enough that there are no significant concerns of contributing to drug resistance with a single agent to which the organism is sensitive.

Some limitations of our study deserve mention. Inherent to its retrospective nature, some data were incomplete. This weakness should be minimized by the presence of standardized history and physical examination forms we employed. Our most important findings, very high rates of active and DRTB, would likely be underestimated by missing data. Our study of cases at St. Michael’s and West Park Hospitals introduces a referral bias, potentially inflating disease and drug-resistance rates. This is a difficult bias to address but likely small in magnitude. Given that the Tibetan-targeted PHD TST program referred all patients to our centers, regardless of CXR results, and that we specialize in TB and providing care to refugees and refugee claimants, it is likely that we assessed most members of this population. Precisely estimating the rate of disease was difficult given the uncertainty surrounding the total number of Tibetans arriving in our area. This is not likely a significant source of error for two reasons. First, we found a similar disease rate to the one observed by Truong et al6 in a similar population. Second, we took measures to provide conservative confidence intervals and the lower bounds still indicated very high rates of disease. It could be speculated that claiming Tibetan ethnic origin may increase the likelihood of a successful refugee claim in Canada, with high-risk patients preferentially claiming Tibetan origin and leading to an overestimate of rates of TB in this population. This is difficult to assess, given the absence of data, but we feel it is not likely significant given the similarity of the rates we observed with those of Truong et al.6

In summary, our experience with a group of newcomers who retained an extremely high risk of active TB and drug resistance, despite an intervening period in a low prevalence country, illustrates the need to maintain a high degree of suspicion for TB in all people who have resided in high-incidence areas. We support calls for the enhancement of targeted screening, treatment of LTBI and ongoing medical surveillance in newcomers from high-risk areas.11 22


   Footnotes
 
Abbreviations: CXR = chest radiograph; DRTB = drug-resistant tuberculosis; LTBI = latent tuberculosis infection; MDRTB = multidrug-resistant tuberculosis; PHD = City of Toronto Public Health Department; TB = tuberculosis; TST = tuberculin skin test

This work was performed at St. Michael’s Hospital and West Park Healthcare Centre, both in Toronto and affiliated with the University of Toronto.

Dr. Marras is a Canadian Lung Association and Canadian Institutes of Health Research postdoctoral fellow, and a trainee in the University of Toronto Department of Medicine Clinician Scientist Program.

Received for publication September 30, 2002. Accepted for publication March 10, 2003.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Dye, C, Scheele, S, Dolin, P, et al (1999) Global burden of tuberculosis estimated incidence, prevalence, and mortality by country. JAMA 282,677-686[Abstract/Free Full Text]
  2. Espinal, MA, Laszlo, A, Simonsen, L, et al Global trends in resistance to antituberculosis drugs. N Engl J Med 2001;344,1294-1303[Abstract/Free Full Text]
  3. Remis, RS, Jamieson, F, Chedore, P, et al Increasing drug resistance of Mycobacterium tuberculosis isolates in Ontario, Canada, 1997–1998. Clin Infect Dis 2000;31,427-432[CrossRef][Medline]
  4. Long, R, Njoo, H, Hershfield, E Tuberculosis: 3. Epidemiology of the disease in Canada. Can Med Assoc J 1999;160,1185-1190[Medline]
  5. Varia, M, Sciberras, J Epidemiology of tuberculosis in Ontario: update 1998. Public Health and Epidemiology Report 2000;11,2-12 . Ontario, Canada:
  6. Truong, DH, Hedemark, LL, Mickman, JK, et al Tuberculosis among immigrants from India and Nepal in Minnesota, 1992–1995. JAMA 1997;277,735-738[Abstract]
  7. World Medical Association Declaration of Helsinki.. Recommendations guiding physicians in biomedical research involving human subjects. JAMA 1997;277,925-926[CrossRef][ISI][Medline]
  8. Canadian tuberculosis standards 4th ed. 1996 Health Canada. Ottawa, Canada:
  9. American Thoracic Society.. Treatment of tuberculosis and tuberculosis infection in adults and children. Am J Respir Crit Care Med 1994;149,1359-1374[Abstract]
  10. American Thoracic Society.. American Thoracic Society/Centers for Disease Control and Prevention targeted tuberculin testing and treatment of latent tuberculosis infection. Am J Respir Crit Care Med 2001;161,S221-S247
  11. Canadian Tuberculosis Standards 5th ed. 2000 Health Canada. Ottawa, Canada:
  12. Bhatia, S, Dranyi, T, Rowley, D Tuberculosis among Tibetan refugees in India. Soc Sci Med 2002;54,423-432[Medline]
  13. DeRiemer, K, Chin, DP, Schecter, GF, et al Tuberculosis among immigrants and refugees. Arch Intern Med 1998;158,753-760[Abstract/Free Full Text]
  14. Wells, CD, Zuber, PLF, Nolan, CM, et al Tuberculosis prevention among foreign-born persons in Seattle-King County, Washington. Am J Respir Crit Care Med 1997;156,573-577[Abstract/Free Full Text]
  15. Zuber, PLF, Knowles, LS, Binkin, NJ, et al Tuberculosis among foreign-born persons in Los Angeles County, 1992–1994. Tuberc Lung Dis 1996;77,524-530[CrossRef][ISI][Medline]
  16. Gilad, J, Borer, A, Riesenberg, K, et al Epidemiology and ethnic distribution of multidrug-resistant tuberculosis in southern Israel, 1992–1997: the impact of immigration. Chest 2000;117,623-625[Free Full Text]
  17. Kempainen, R, Nelson, K, Williams, DN, et al Mycobacterium tuberculosis disease in Somali immigrants in Minnesota. Chest 2001;119,176-180[Abstract/Free Full Text]
  18. Manns, BJ, Fanning, EA, Cowie, RL Antituberculous drug resistance in immigrants to Alberta, Canada, with tuberculosis, 1982–1994. Int J Tuberc Lung Dis 1997;1,225-230[Medline]
  19. Talbot, EA, Moore, M, McCray, E, et al Tuberculosis among foreign-born persons in the United States, 1993–1998. JAMA 2000;284,2894-2900[Abstract/Free Full Text]
  20. Institute of Medicine (U.S.), Committee on the Elimination of Tuberculosis in the United States.. Ending neglect: the elimination of tuberculosis in the United States. 2000 National Academy Press. Washington, DC:
  21. Canadian Tuberculosis Committee.. Canadian guidelines for the investigation and follow-up of individuals under medical surveillance for tuberculosis after arrival in Canada. Can Commun Dis Rep 2001;27,157-165[Medline]
  22. Citizenship and Immigration Canada.. Building on a strong foundation for the 21st century: new directions for immigration and refugee policy and legislation. 1998 Minister of Public Works and Government Services. Ottawa, Canada:
  23. Khan, K, Muennig, P, Behta, M, et al Global drug-resistance patterns and the management of latent tuberculosis infection in immigrants to the United States. N Engl J Med 2002;347,1850-1859[Abstract/Free Full Text]
  24. Schwartzman, K, Menzies, D Tuberculosis screening of immigrants to low-prevalence countries: a cost effectiveness analysis. Am J Respir Crit Care Med 2001;161,780-789




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Marras, T. K.
Right arrow Articles by Yang, J. W.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Marras, T. K.
Right arrow Articles by Yang, J. W.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS