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RESEARCH |
Guy B. Marks, Jun Bai, and Sheila E. Simpson are with South Western Sydney Area Health Service, Sydney, Australia. Guy B. Marks is also with the Institute of Respiratory Medicine, University of Sydney, Sydney, Australia. At the time of this study, Gregory J. Stewart was with Central Sydney Area Health Service, Sydney, Australia. Elizabeth A. Sullivan is with the School of Paediatrics, University of New South Wales, Sydney, Australia.
Correspondence: Requests for reprints should be sent to Guy B. Marks, PhD, FRACP, Chest Clinic, Liverpool Hospital, PO Box 103, NSW 2170 Australia (e-mail: g.marks{at}unsw.edu.au).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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Objectives. This study assessed the effectiveness of postmigration screening for the control of tuberculosis (TB) among refugee migrants.
Methods. We conducted a historical cohort study among 24 610 predominantly Southeast Asian refugees who had arrived in Sydney, Australia, between 1984 and 1994. All had been screened for TB before arrival and had radiologic follow-up for 18 months after arrival. Incident cases of TB were identified by record linkage analysis with confirmatory review of case notes.
Results. The crude annual incidence rate over 10-year follow-up was 74.9 per 100 000 person-years. Only 29.6% of the cases were diagnosed as a result of routine follow-up procedures.
Conclusions. Enhanced passive case finding is likely to be more effective than active case finding for the control of TB among refugees.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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All refugees 16 years and older, as well as symptomatic children, had a chest x-ray performed before departure for Australia. Those in whom currently or recently active TB was suspected began receiving antituberculous drug therapy at that time. Soon after their arrival in New South Wales, Australia, all refugees had further screening for TB at the Refugee Screening Unit or at Liverpool Chest Clinic. The results of this initial postmigration screening, which comprised a tuberculin skin test, examination for a BCG vaccine scar, and a chest x-ray, were recorded in a logbook. Tuberculin skin test reaction size was recorded for all reactions 10 mm or greater. Tuberculin skin test reaction sizes in the range of 0 to 9 mm were recorded as "negative". Chest x-rays were recorded as "satisfactory" or "not satisfactory". These records formed the basis of the database of screened refugees referred to below.
All refugees were then followed up by their local area chest clinics at 6 months and 18 months after initial postarrival screening. This follow-up screening comprised annual chest x-rays and, in certain cases, clinical examinations. For children younger than 14 years, chest x-rays were performed only if the tuberculin skin test reaction was 10 mm or greater. Refugees who did not attend follow-up appointments were sent reminder letters, telephoned, and, when necessary, visited at home to encourage them to attend. At the discretion of the attending medical officer, the period of screening continued beyond 18 months after arrival for some refugees.
Cases of TB arising in the cohort were identified by a record linkage analysis that used a database of screened refugees and a database of cases of TB reported to the New South Wales Department of Health during the period 1984 through 1998.5,6 We reviewed notification data, case notes, and x-ray films for the notified cases of TB identified from the refugee cohort to confirm or refute the diagnosis of active TB.5,6
The source of discovery of the case (i.e., referral because of symptomatic presentation or detection by screening procedures) was ascertained from case records and notification details.
To be certain that cases of TB arising in this cohort would have been reported to the New South Wales Department of Health, we sought to confirm that the members of the cohort were predominantly alive and living in New South Wales throughout the study period. We attempted to trace the current location of 200 cohort members selected at random from the study population.
The sensitivity and specificity of various cutpoints for a positive tuberculin skin test reaction (10, 15, and 20 mm) and an abnormal chest x-ray at initial postarrival screening for predicting the subsequent development of TB were calculated. Number needed to screen to detect a case was calculated as the inverse of the incidence rate. This analysis was limited to the cases arising within 18 months of arrival—that is, the period of routine postarrival screening.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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Of the random sample of 200 cohort members whose whereabouts were traced in 1998, 171 (85.5%) were living in New South Wales.
By June 30, 1998, after an average follow-up interval of 10.3 years, 290 members of this cohort had been reported as a TB case. Of these, 189 (65.2%) were confirmed as cases of TB, representing an overall incidence rate of 74.9 per 100 000 person-years. Sixty-seven percent of the active cases were pulmonary; of these, 50% were smear positive on sputum examination, and 25% were smear negative but culture positive.
Fifty-five cases, 29.1% of all observed cases, occurred within 1 year of arrival, and 124 (65.6%) occurred within 5 years of arrival. The incidence rate in the first year was 223.8 per 100 000, and the average annual incidence rate over the first 5 years after arrival was 102.1 per 100 000.
Two thirds of the cases (126) were identified as a result of symptomatic presentation, usually through primary care. Most of these arose after the 18-month period of routine screening (Table 1
). Fifty-six cases (29.6%) were diagnosed and reported as a result of the routine screening program. The remaining 7 cases (3.7%) were identified as a result of contact tracing investigations.
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shows the sensitivity and specificity of various tuberculin skin test cutpoints, the presence of an abnormal chest x-ray, and the combination of these findings for predicting subsequent development of TB. No single finding or combination of findings had both high sensitivity and high specificity.
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Restriction of follow-up screening to population subgroups selected on the basis of a positive initial tuberculin skin test or abnormal chest x-ray findings would have reduced the number screened per detected case (data not shown), but the number of cases actually detected would be reduced proportionately.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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The validity of this method of assessing the effectiveness of screening is based on the assumption that most of the cases of TB arising in this cohort represented reactivation of TB that was latent at the time of arrival in Australia. Although transmission, and hence infection or reinfection, may have occurred in Australia or during visits back to the country of origin, this transmission timing probably has been even less common in the Sydney environment than it was in San Francisco, Calif.7,8
A strength of this study was the sensitivity and specificity of case ascertainment. Evidence indicates that the overwhelming majority of the patients treated for TB in New South Wales were reported to the Department of Health and were identified as cases in our study.9,10 This is, in part, attributable to the fact that the great majority of TB treatment (for all ages and for all sites) is given free of charge through chest clinics in New South Wales. The validity of this database as a complete, and thus sensitive, record of cases of TB occurring in New South Wales is supported by the observation that recent intensified surveillance, including tracing through records of sale of antituberculous drugs, did not result in any detectable increase in the identification rate. The specificity of the diagnosis of TB cases in this analysis was enhanced by review of case records of reported cases and reassessment of the diagnosis based on the criteria specified in the Methods section of this report.5,6 Finally, the finding that the cohort has remained intact, within New South Wales, during the period of follow-up supports the likelihood of complete ascertainment of incident cases.
Even if the period and intensity of postmigration screening were increased, it is unlikely that active case finding would be a cost-effective strategy for the control of TB in this population. Enhancing the capacity for passive case finding by increasing awareness of the diagnosis, particularly among primary care physicians attending the refugee and migrant communities, and improving access to specialist services for the diagnosis and management of TB is likely to be a more effective strategy. Preventive therapy with isoniazid in tuberculin skin test–positive refugees may have a role in the control of TB in situations in which passive case finding is ineffective and there are long delays to diagnosis. However, to prevent a substantial proportion of incident cases, this strategy would be costly because it would require the administration of chemoprophylaxis to, and medical review of, a large proportion of incoming refugees.
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Acknowledgments |
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Data on TB notifications were supplied by the NSW Department of Health.
The study protocol was approved by the Research Ethics Committees of South Western Sydney Area Health Service and the NSW Department of Health.
We thank Dr C. M. Mukerjee, who was the physician at the Liverpool Chest Clinic during the period in which baseline investigations were undertaken with the refugees who formed the cohort reported here.
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Footnotes |
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Accepted for publication July 12, 2001.
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References |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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2. Zuber P, McKenna M, Binkin N, Onorato I, Castro K. Long-term risk of tuberculosis among foreign-born persons in the United States. JAMA.1997;278:304–307.[Abstract]
3.
McKenna M, McCray E, Onorato I. The epidemiology of tuberculosis among foreign-born persons in the United States, 1986–93. N Engl J Med.1995;332:1071–1076.
4. MacIntyre C, Dwyer B, Streeton J. The epidemiology of tuberculosis in Victoria. Med J Aust.1993;159:672–677.[Medline]
5. Bai J, Marks G, Stewart G, Simpson S, Sullivan E. Specificity for notification of tuberculosis among screened refugees in NSW. Aust N Z J Public Health.1999;23:410–413.[Medline]
6.
Marks G, Bai J, Simpson S, Sullivan E, Stewart G. Incidence of tuberculosis among a cohort of tuberculinpositive refugees in Australia: re-appraising the estimates of risk. Am J Respir Crit Care Med.2000;162:1851–1854.
7.
Chin D, DeRiemer K, Small P, et al. Differences in contributing factors to tuberculosis incidence in US-born and foreign-born persons. Am J Respir Crit Care Med.1998;158:1797–1803.
8. Alperstein G, Fett M, Reznik R, Thomas M, Senthil M. The prevalence of tuberculosis infection among year 8 schoolchildren in inner Sydney in 1992. Med J Aust.1994;160:197–201.[Medline]
9. Stewart G. The Incidence of Tuberculosis in the Southern Metropolitan Region of Sydney, NSW 1976–1986 [master's treatise]. Sydney, Australia: University of Sydney; 1990.
10. Plant A, Christopher P, Richards G, et al. The acquired immunodeficiency syndrome: a TB threat? Med J Aust.1988;148:609–615.[Medline]
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