three controls had to live
at three different addresses. When more than one child/
adolescent was eligible in the same household the one
whose month of birth was closer to that of the case would
be selected. When the child/adolescent was not home an
appointment to another visit was made. Controls were
matched within the age groups 7–9, 10–14 and 15–19
years. The sole exclusion criterion for controls was a diagnosis
of TB (none was excluded).