How easily does tuberculosis spread?

My boyfriend's best friend was diagnosed with tuberculosis. The friend is fine; his only symptom was a persistent cough, and he's on antibiotics now. How likely is it that others in our circle of friends have been infected too? My understanding of TB is that it has a latency period with no symptoms, and then can progress to symptomatic TB years later. Should the infected person's close associates be concerned about latent infections? Should we only be concerned if we have symptoms?