These three studies all show that the risk of a contact person to become infected is highest if the source case was smear-positive (s+/c+ indicates sputum smear positive and sputum culture positive) and that patients culture-only-positive (s-/c+) infected their contacts to a much lesser degree.

The absolute difference in the proportion of infected contacts between these studies is not important to consider as the studies were done at different times, in different locations, and perhaps with different definitions what constituted a "contact".

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