Genarally preventive TB medicines are not given if you are healthy otherwise as these should be used very carefully to avoid developing drug resistant TB. These are only given to people whose immunity is compromised or to a breast fed infant if mother is suffering from sputum positive TB. In your case you have to observe certain precautions like using a face mask, frequent hand washing and ensuring that patients suffering from sputum positive TB also use face mask. From time to time you have to get yourself screened by doing a chest xray and sputum examination to ensure that you have not developed the disease. Even if you take preventive TB medicines in the form of INH and Rifampicin for a period of 4 to 6 months there is no guarantee that you well not be exposed to the MTB again and wo`nt develop the disease and then the chances of drug resistance will be higher.