Journal Article

Tuberculosis Transmission by Patients with Smear-Negative Pulmonary Tuberculosis in a Large Cohort in The Netherlands

Alma Tostmann, Sandra V. Kik, Nico A. Kalisvaart, Maruschka M. Sebek, Suzanne Verver, Martin J. Boeree and Dick van Soolingen

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 47, issue 9, pages 1135-1142
Published in print November 2008 | ISSN: 1058-4838
Published online November 2008 | e-ISSN: 1537-6591 | DOI: http://dx.doi.org/10.1086/591974
Tuberculosis Transmission by Patients with Smear-Negative Pulmonary Tuberculosis in a Large Cohort in The Netherlands

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Background. Sputum smear microscopy is commonly used for diagnosing tuberculosis (TB). Although patients with sputum smear–negative TB are less infectious than patients with smear-positive TB, they also contribute to TB transmission. The objective of this study was to determine the proportion of TB transmission events caused by patients with smear-negative pulmonary TB in The Netherlands.

Methods. All patients in The Netherlands with culture-confirmed TB during the period 1996–2004 were included in this study. Patients with identical DNA fingerprints in Mycobacterium tuberculosis isolates from sputum samples were clustered. The first patients in a cluster were considered to be the index patients; all other patients were considered to have secondary cases. In addition, we examined transmission from sources by conventional contact tracing.

Results. We analyzed 394 clusters with a total of 1285 patients. On the basis of molecular linkage only, 12.6% of the secondary cases were attributable to transmission from a patient with smear-negative TB. The relative transmission rate among patients with smear-negative TB, compared with patients with smear-positive TB, was 0.24 (95% confidence interval, 0.20–0.30). Secondary cases in clusters with an index patient with smear-negative TB more frequently had smear-negative status (odds ratio, 1.86; 95% confidence interval, 1.18–2.93), compared with secondary cases in clusters with an index patient with smear-positive TB. Conventional contact tracing revealed that 26 (6.2%) of the 417 sources, as identified by the Municipal Health Services, had smear-negative TB.

Conclusions. In The Netherlands, patients with smear-negative, culture-positive TB are responsible for 13% of TB transmission. Countries that have ample resources should expand their TB-control efforts to include prevention of transmission from patients with smear-negative, culture-positive pulmonary TB.

Journal Article.  4104 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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