It is not surprising that cough frequency of a tuberculosis patient affects the risk of contacts to become infected.

The diameter of droplet nuclei plays an important role whether infection will take place or not.  They must be able to reach the alveolus as lodging in the bronchial tree is an inefficient mechanism to establish infection.  The coarser the nuclei, the less likely for them to reach the alveolus.  Particles of less than 10 micrometer diameter (as half of those produced by coughing are) are fairly efficient in reaching the alveolar surface. 

It should be stressed, however, that other factors than cough, in particular bacterial load, will have an important influence on the infectiousness of patients as will be seen.

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