Measures
Data were collected on age, gender, BCG vaccination status
(scar or documentation of vaccination record) and M tuberculosis
exposure. A household tuberculosis index case was defined as a
person aged >15 years with bacteriologically positive tuberculosis
(sputum smear and/or culture positive) diagnosed at the R/
U clinic during the previous 3 months and currently living in
the same or neighbouring physical dwelling located on the same
residential property. Caregivers and adult participants were
interviewed to determine the participant’s extent of contact
with the index case during a typical week. A previously
published M tuberculosis contact score18 was modified for use
in this study setting. The modified M tuberculosis contact score
was based on the assumptions that the gradient ofMtuberculosis
exposure was a composite function of the infectivity of the
index case, the duration of exposure and the proximity of
exposure (table 1). The mean contact score was calculated for
each participant. After exploration of cut-off values, the score
was dichotomised as low (,4) vs high exposure (>4) based on
the score distribution in the sample.