Transmission of multi drug-resistant TB (MDR-TB) within the household is less likely to occur compared to drug-susceptible TB.
A study published in the journal PLOS Medicine found that MDR-TB surely has "relatively low fitness (be less capable of spreading) compared with drug-susceptible TB."
Previous animal and laboratory studies, as well as molecular epidemiology studies reveal that the fitness level of drug-susceptible TB bacteria to spread within populations was higher than MDR-TB bacteria.
"The low relative fitness of MDR-TB estimated by this study improves the chances of controlling drug-resistant tuberculosis. However, fitter multi drug-resistant strains that emerge over time may make this increasingly difficult," writes Louis Grandjean, the first author from the Imperial College London. "The greater the relative fitness of drug-resistant TB, the greater the size of the drug-resistant epidemic."
The study carried out in South Lima and Callao, Peru followed up people living in the same household as the index patient for three long years (2010-2013). The study tracked 213 MDR-TB index patients and 1,055 of their household contacts. Also, 487 index patients and their 2,362 household contacts in the case of drug-susceptible TB patients.
The hazard ratio for TB disease for household contacts of MDR-TB index cases was half that of those with drug-susceptible TB. While only 35 of 213 of MDR-TB contacts developed MDR-TB disease, 114 of 2,362 drug-susceptible TB contacts developed disease.
Male household contacts and those who slept in the same room as the index patient had higher incidence of active TB than those who did not share a sleeping room. Also, household contacts who had diabetes or HIV or who had previous history of active TB had higher incidence of active TB.
The WHO and the Indian TB control programme (RNTCP) insist that all household contacts of a TB index patient should be screened for TB disease when the index patient is diagnosed.