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Abstract
BackgroundStudies examining the transmission of multidrug-resistant tuberculosis (MDR-TB) strains have yielded conflicting results.MethodsWe 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.ResultsOf 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.ConclusionContacts 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.
Highlights
Studies examining the transmission of multidrug-resistant tuberculosis (MDR-TB) strains have yielded conflicting results
MDR-TB population We identified 35 MDR-TB cases from the BC Centre for Disease Control (BCCDC) registry between 1990 and 2008 (Table 1)
Five close contacts developed TB disease during follow-up; fully susceptible M. tuberculosis was isolated from 4 cases and the fifth case was diagnosed based on clinical criteria
Summary
Studies examining the transmission of multidrug-resistant tuberculosis (MDR-TB) strains have yielded conflicting results. Contact tracing studies consistently report a significant proportion of contacts with TB disease that demonstrate a distinct resistance profile from their identified MDRTB source, indicating that not all supposed transmission events involve MDR-TB strains [12,14,15,16,17,18,19,20]. Despite this discrepancy, there is considerable evidence to support human-to-human MDR-TB strain transmission. Appropriate preventative treatment of MDR-TB contacts remains unclear, as the relative infectivity MDR-TB strains is unknown and no high quality evidence exists to guide treatment of latent TB infection (LTBI) in contacts of drug resistant cases [22]
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