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Open Access Highly Accessed Research article

Long term follow-up of drug resistant and drug susceptible tuberculosis contacts in a Low incidence setting

James Johnston12*, Andrew Admon3, Amir Ibrahim2, Kevin Elwood1, Patrick Tang4, Victoria Cook12 and Mark Fitzgerald2

Author affiliations

1 Division of Tuberculosis Control, British Columbia Centre for Disease Control, Vancouver, BC, Canada

2 Department of Medicine, University of British Columbia, Vancouver, BC, Canada

3 Department of Internal Medicine, University of Michigan Health System, Ann Arbor, MI, 48109, USA

4 Department of Pathology & Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada

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Citation and License

BMC Infectious Diseases 2012, 12:266  doi:10.1186/1471-2334-12-266

Published: 22 October 2012

Abstract

Background

Studies examining the transmission of multidrug-resistant tuberculosis (MDR-TB) strains have yielded conflicting results.

Methods

We examined transmission of MDR-TB strains using contact tracing data from a low incidence setting. Contacts of MDR-TB cases diagnosed in British Columbia, Canada, from 1990-2008 were identified through a provincial tuberculosis (TB) registry. Tuberculin skin test (TST) results and TB disease incident rates were determined for contacts. For comparison, TB disease incident rates and TST results were measured in close contacts of isoniazid mono-resistant (HMR-TB) and drug susceptible TB (DS-TB) cases.

Results

Of 89 identified close contacts of MDR-TB patients, 5 patients (6%) developed TB disease and 42 (47%) were TST positive. The incidence rate of TB disease (3%, p = 0.31) and TST positivity (49%, p = 0.82) were similar in contacts of HMR-TB cases. Compared with MDR-TB contacts, DS-TB contacts had lower incidence rate of TB disease (2%, p = 0.04) and TST positivity (32%, p < 0.01). All MDR-TB contacts with culture positive TB diagnosed in follow-up were drug-susceptible; three of six HMR-TB contacts with culture positive TB were HMR-TB. Multivariate analysis demonstrated that contact with MDR-TB (adjusted OR 1.72; 95%CI 1.05-2.81) and HMR-TB (adjusted OR 1.99; 95%CI 1.48-2.67) was associated with TST positivity. In addition, adult age, male gender, BCG positivity, source case sputum smear positivity, foreign birth and fewer contacts per source case were significantly associated with TST positivity in the multivariate model.

Conclusion

Contacts of MDR-TB and HMR-TB patients in a low incidence setting show high rates of TST positivity and TB disease but low rates of drug resistance.

Keywords:
Tuberculosis; Multidrug-resistant; Contact investigation; Epidemiology; Latent tuberculosis