I agree with Dr. Ashutosh that a TB pleural effusion usually implies good immunity. I have come across quite a few such patients, relatively healthy and complaining of only minimal symptoms.  The pleural effusion is actually an immune response to the tuberculous antigens released into the pleural space. But, one must not forget that the antigens are most commonly released from foci in the underlying lung.  Now, if there are such infectious foci in the lung, can't the patient be infectious? I agree that these foci might be quite small (may even be beyond the limits of our current diagnostic capabilities!) and may not be as infectious as a cavitary lesion. But still, will there be a risk (albeit small) of infection to the patient's contacts (if the patient is not on ATT or during the early part of ATT, when the patient is still infectious)? This question came to my mind when one of my patients requested me to give a document stating that he is not infectious to others (He had to produce the document in his office to continue working!). I was initially thinking along the same lines of Dr. Ashutosh and cleared him as there was no obvious lung lesion in the CXR (I agree that the caveat which GrimDoc had mentioned, while interpreting such CXRs/CTs is important here!).  After doing a bit of literary research, I feel that I should have advised him to take leave for 2-3 weeks (sufficient enough time for the ATT to render him non-infectious) as there is a possibility that he might be infectious. What is the right course of action in this situation? Another question is, "What would you do for the household contacts?" Would you screen them, considering the patient to be infectious or would you ignore them as the patient is non-infectious? (For household contacts of an infectious source,  WHO guidelines  advise to offer treatment (ATT) for symptomatic patients (adult or child) and INH preventive treatment (IPT) for asymptomatic children <6 year old. 
Posted by Doc KTP