Multidrug-resistant TB appears less transmissible in households than drug-susceptible TB
Some strains of multidrug resistant tuberculosis (MDRTB) may have a lower fitness (be less capable of spreading) than drug-susceptible tuberculosis bacteria, according to a study published this week in PLOS Medicine. The study, conducted by Louis Grandjean of Imperial College London, and colleagues, compared new tuberculosis cases among household contacts of tuberculosis patients in South Lima and Callao, Peru to determine the relative fitness of MDRTB versus drug-susceptible tuberculosis.
The study followed 1,055 household contacts of 213 individuals
with MDRTB infection (defined by resistance to the drugs
rifampicin and isoniazid), and 2,362 household contacts of 487
individuals with drug-susceptible tuberculosis for up to three
years. Thirty-five (3.3%) of MDRTB contacts and 114 (4.8%) of
drug-susceptible tuberculosis contacts developed tuberculosis.
When the authors adjusted for risk factors such as HIV status,
socio-economic status, and sputum smear grade (a measure
associated with higher risk of transmission) of the index case,
household contacts of MDRTB cases were 44% less likely to
contract tuberculosis than were contacts of drug-susceptible
tuberculosis cases.
Previous laboratory findings as
well as estimates of fitness based on genetic clustering of
strains in the population suggested a lower relative fitness for
MDRTB compared to drug-susceptible tuberculosis, but few studies
have directly measured the incidence of second cases of
tuberculosis among contacts of both MDRTB and drug-susceptible
tuberculosis. The researchers note that they did not have
genoptyping data for infections in household contacts, so some
of these secondary cases may have been transmitted from someone
outside the household. Additionally, transmission dynamics may
be different in the community setting outside households or in
different countries, and more fit MDRTB strains may emerge in
the future.
Despite these limitations, the authors
say that their findings are "welcome and encouraging news for
tuberculosis control programs and health services attempting to
contain the spread of MDRTB."
Journal Reference:
- Louis Grandjean, Robert H. Gilman, Laura Martin, Esther Soto, Beatriz Castro, Sonia Lopez, Jorge Coronel, Edith Castillo, Valentina Alarcon, Virginia Lopez, Angela San Miguel, Neyda Quispe, Luis Asencios, Christopher Dye, David A. J. Moore. Transmission of Multidrug-Resistant and Drug-Susceptible Tuberculosis within Households: A Prospective Cohort Study. PLOS Medicine, 2015; 12 (6): e1001843 DOI: 10.1371/journal.pmed.1001843
Source:
ScienceDaily
