TABLE 6. EPIDEMIOLOGICAL CIRCUMSTANCES IN WHICH AN EXPOSED PERSON IS ATINCREASED RISK OF INFECTION WITH DRUG-RESISTANT Mycobacterium Tuberculosis* • Exposure to a person who has known drug-resistant tuberculosis • Exposure to a person with active tuberculosis who has had prior treatment for tuberculosis (treatment failure or relapse) and whose susceptibility test results are not known • Exposure to persons with active tuberculosis from areas in which there is a high prevalence of drug resistance • Exposure to persons who continue to have positive sputum smears after 2 months of combination chemotherapy • Travel in an area of high prevalence of drug resistance * This information is to be used in deciding whether or not to add a fourth drug (usually EMB) for children with active tuberculosis, not to infer the empiric need for a second-line treatment regimen