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J Infect Dis. 2011 May 1;203(9):1249-55. doi: 10.1093/infdis/jir013. Epub 2011 Mar 4.

Mycobacterial factors relevant for transmission of tuberculosis.

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  • 1Tuberculosis Reference Laboratory, Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven.



Tuberculosis (TB) transmission is associated with patient-related risk factors. However, DNA fingerprint analysis has provided anecdotal evidence suggesting a role for bacteriological factors.


To examine the importance of the bacteriological component in TB transmission, we investigated the number of tuberculin skin test-positive (TST induration, ≥ 10 mm) contacts and secondary cases observed in contact investigations around TB cases in relation to the size of the genotype cluster the patient belonged to at the time of diagnosis. We also compared the number of TST-positive contacts and secondary cases of patients with drug-resistant and drug-susceptible TB.


Larger clusters were independently associated with an increased number of positive contacts. The mean number of positive contacts ranged from 3.8 for clusters of 2 cases, to 4.7 for clusters of 3-10 cases, to 6.0 for cases in clusters of >10 cases (mean increase in number of positive contacts for every extra case in the cluster, 0.21; 95% confidence interval, 0.09-0.26). The mean number of positive contacts was significantly lower among index cases with isoniazid-monoresistant TB (1.6) than among index cases with pan-susceptible TB (4.6; relative number, 0.45; 95% confidence interval, 0.22-0.92).


These results suggest that spread of tuberculosis also depends on bacteriological factors.

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