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Correspondence |

On the Role of Chest CT Scanning in a TB Outbreak Investigation FREE TO VIEW

Ben J. Marais, MD, PhD
Author and Funding Information

Department of Paediatrics and Child Health, Faculty of Health Sciences, Stellenbosch University.

Correspondence to: Ben J. Marais, MD, PhD, Department of Paediatrics and Child Health, Faculty of Health Sciences, Stellenbosch University, PO Box 19063, Tygerberg, 7505, South Africa; e-mail: bjmarais@sun.ac.za


Financial/nonfinancial disclosures: The author has reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2011 American College of Chest Physicians


Chest. 2011;139(1):229. doi:10.1378/chest.10-1775
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To the Editor:

A recent article in CHEST (May 2010) by Lee et al1 reported the use of high-resolution chest CT (HRCT) scanning during a TB outbreak investigation. They found that nine of 18 (50%) cases diagnosed with active TB would have been missed without the use of HRCT scanning and concluded that inclusion of HRCT scanning seems helpful to reliably identify cases with active TB during an outbreak investigation. Routine use of HRCT scanning will add cost, increase radiation exposure, and undermine confidence in existing screening tools where HRCT scanning is unavailable, but the most important reason for caution is the likely absence of clinical relevance.

Patients with asymptomatic “HRCT confirmed active TB” present a case-definition dilemma, because the natural history of Mycobacterium tuberculosis infection demonstrates that transient phenomena, such as parenchymal consolidation and/or hilar adenopathy (even M tuberculosis excretion), occur quite frequently after recent primary infection.2,3 Only a small percentage of these asymptomatic “patients” progress to active disease on long-term follow-up.2,3 Therefore, it is not unexpected that HRCT scanning identifies a subset of recently exposed individuals with visible parenchymal and/or lymph node involvement despite being asymptomatic and having a normal chest radiograph. However, the clinical relevance of these findings remains questionable—whether it represents transient phenomena or is truly indicative of active disease, and whether treatment with combination therapy is warranted.

None of the patients with a normal chest radiograph and lesions suggestive of active TB on HRCT scan were sputum smear or culture positive for M tuberculosis, indicating uncertain diagnosis and/or low organism loads. The United States Public Health Service Tuberculosis Prophylaxis preventive therapy trial conducted in the 1950s demonstrated that isoniazid monotherapy prevented progression to symptomatic disease in child TB contacts, despite the presence of radiologic signs suggestive of recent primary infection and/or minimal disease.4 This provides the rationale for symptom-based screening approaches in children.5 In certain high-risk groups the use of sensitive screening tools may well be warranted, but because subclinical transient phenomena may be detected and treated with increased regularity the routine use of HRCT scanning to screen asymptomatic TB contacts for active disease requires rigorous scrutiny. Given the current evidence, cost, and potential risks involved, there is no role for HRCT scanning as a routine screening test during TB outbreak investigations.

Lee SW, Jang YS, Park CM, et al. The role of chest CT scanning in TB outbreak investigation. Chest. 2010;1375:1057-1064. [CrossRef] [PubMed]
 
Gedde-Dahl T. Tuberculous infection in the light of tuberculin matriculation. Am J Hyg. 1952;562:139-214. [PubMed]
 
Marais BJ, Gie RP, Schaaf HS, et al. The natural history of childhood intra-thoracic tuberculosis: a critical review of the pre-chemotherapy literature. Int J Tuberc Lung Dis. 2004;84:392-402. [PubMed]
 
Ferebee S, Mount FW, Anastasiades A. The United States Public Health Service Tuberculosis Prophylaxis Trial collaborators. Prophylactic effects of isoniazid on primary tuberculosis in children; a preliminary report. Am Rev Tuberc. 1957;766:942-963. [PubMed]
 
Kruk A, Gie RP, Schaaf HS, Marais BJ. Symptom-based screening of child tuberculosis contacts: improved feasibility in resource-limited settings. Pediatrics. 2008;1216:e1646-e1652. [CrossRef] [PubMed]
 

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References

Lee SW, Jang YS, Park CM, et al. The role of chest CT scanning in TB outbreak investigation. Chest. 2010;1375:1057-1064. [CrossRef] [PubMed]
 
Gedde-Dahl T. Tuberculous infection in the light of tuberculin matriculation. Am J Hyg. 1952;562:139-214. [PubMed]
 
Marais BJ, Gie RP, Schaaf HS, et al. The natural history of childhood intra-thoracic tuberculosis: a critical review of the pre-chemotherapy literature. Int J Tuberc Lung Dis. 2004;84:392-402. [PubMed]
 
Ferebee S, Mount FW, Anastasiades A. The United States Public Health Service Tuberculosis Prophylaxis Trial collaborators. Prophylactic effects of isoniazid on primary tuberculosis in children; a preliminary report. Am Rev Tuberc. 1957;766:942-963. [PubMed]
 
Kruk A, Gie RP, Schaaf HS, Marais BJ. Symptom-based screening of child tuberculosis contacts: improved feasibility in resource-limited settings. Pediatrics. 2008;1216:e1646-e1652. [CrossRef] [PubMed]
 
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