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Correspondence |

Insufficient Evidence for Chest CT Scan in TB Outbreak Investigation FREE TO VIEW

Elizabeth Joekes, MD; Geraint Davies, PhD, DTM&H; Henry C. Mwandumba, PhD, DTM&H; S. Bertel Squire, MBBChir, MD
Author and Funding Information

From the Department of Radiology (Dr Joekes), the Royal Liverpool University Hospital; the Department of Infectious Diseases (Drs Davies and Mwandumba), the University of Liverpool; and the Department of Clinical Tropical Medicine (Dr Squire), the Liverpool School of Tropical Medicine.

Correspondence to: Elizabeth Joekes, MD, Department of Radiology, The Royal Liverpool and Broadgreen University Hospitals NHS Trust, Prescot St, Liverpool, L7 8XP, England; e-mail: elizabeth.joekes@rlbuht.nhs.uk


Financial/nonfinancial disclosures: The authors have 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 (www.chestpubs.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;138(1):234-235. doi:10.1378/chest.10-0077
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To the Editor:

We read with interest the article by Lee et al1 in CHEST (May 2010) evaluating the role of chest CT scans in TB outbreak investigation. In a cohort of 87 patients with TB, 18 cases of active TB were diagnosed. Nine of these patients had normal chest radiographs but showed lesions suggestive of active TB on high-resolution CT (HRCT) scans. The authors conclude that inclusion of HRCT scanning in outbreak investigation may be helpful in differentiating active TB from latent TB infection more reliably. However, several aspects of this study are flawed and require further discussion.

First, a gold standard for the diagnosis of active TB on HRCT scans was not set. The presence of cavities, branching linear opacities, or multiple noncalcified nodules was used as defining active TB. These findings may indeed indicate active TB in the correct clinical setting but are by no means 100% specific.2,3 In only three out of nine cases was active TB confirmed by culture examinations. In addition, both film readers were blinded to clinical information but not to the aims of the study, introducing observer bias for a diagnosis of active TB. This may also explain the exceptionally good interobserver agreement.

Second, a control group of patients without a suspicion of possible active TB (negative tuberculin skin test and γ interferon test) was not included. The prevalence and significance of the chosen HRCT scan criteria in an asymptomatic population, with an equally large proportion of smokers, is unknown. The relatively high number of incidentally diagnosed pneumonias in the HRCT scan group (5/50) is an indication that diseases other than active TB are relatively frequent in this cohort.

Third, follow-up of all cases, including those with a normal chest radiograph initially, was performed using radiographs rather than HRCT scans. The treatment response of the positive cases on HRCT scans, which could have served as an additional measure to confirm the diagnosis, remains unknown.

Last, of the nine additional cases diagnosed with HRCT scans, seven had clinical symptoms suggestive of a diagnosis of active TB and a positive γ interferon test result. The three culture-proven cases were all in this group. Even with a negative chest radiograph, it is debatable whether these patients would have been diagnosed and treated as latent infections in an outbreak investigation without the additional HRCT scan. Only two cases were asymptomatic patients with a positive γ interferon test. In neither of these was active TB proven, leading to the possibility that these may represent false-positive test results.

In conclusion, the previously documented higher accuracy of HRCT scans compared with chest radiographs in the detection of active pulmonary TB4 is again noted in this study. However, as a result of study design and the methodologic flaws described previously, the aim of the study to elucidate the role of HRCT scanning in outbreak investigation is not met. The conclusion that HRCT scans may differentiate active TB from latent TB infection in outbreak investigation is insufficiently supported by the data. As the authors mention in their discussion, the impact of additional HRCT scanning in TB outbreak investigation can only be assessed by randomized controlled trials with the incidence of active TB in each group of patients as the end point. In view of the high cost of CT scanning, particularly in a screening environment, such trials should include assessment of cost effectiveness. Risks associated with increased exposure to radiation will also have to be taken into account. At present, there is insufficient evidence to justify the inclusion of HRCT scanning in TB outbreak investigation.

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]
 
Okada F, Ando Y, Yoshitake S, et al. Clinical/pathologic correlations in 553 patients with primary centrilobular findings on high-resolution CT scan of the thorax [abstract]. Chest. 2007;1326:1939-1948. [CrossRef] [PubMed]
 
Rossi SE, Franquet T, Volpacchio M, Giménez A, Aguilar G. Tree-in-bud pattern at thin-section CT of the lungs: radiologic-pathologic overview. Radiographics. 2005;253:789-801. [CrossRef] [PubMed]
 
Jeong YJ, Lee KS. Pulmonary tuberculosis: up-to-date imaging and management. AJR Am J Roentgenol. 2008;1913:834-844. [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]
 
Okada F, Ando Y, Yoshitake S, et al. Clinical/pathologic correlations in 553 patients with primary centrilobular findings on high-resolution CT scan of the thorax [abstract]. Chest. 2007;1326:1939-1948. [CrossRef] [PubMed]
 
Rossi SE, Franquet T, Volpacchio M, Giménez A, Aguilar G. Tree-in-bud pattern at thin-section CT of the lungs: radiologic-pathologic overview. Radiographics. 2005;253:789-801. [CrossRef] [PubMed]
 
Jeong YJ, Lee KS. Pulmonary tuberculosis: up-to-date imaging and management. AJR Am J Roentgenol. 2008;1913:834-844. [CrossRef] [PubMed]
 
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