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Bacteriologic Conversion of Sputum among Tuberculosis Patients -- United States

By the end of May 1985, information was available from 44 state health departments, the District of Columbia, Guam, Puerto Rico, and the Virgin Islands on bacteriologic conversion of sputum from positive to negative for 12,637 tuberculosis patients. All patients had begun treatment in 1983 for pulmonary tuberculosis and represented 73% of the total sputum-positive pulmonary tuberculosis cases reported during that year. Within 3 months of starting treatment, 54% had negative sputum.

Within 6 months of beginning therapy, 10% of the patients had moved or died. Of the remaining 11,410, 75% had converted to sputum negative; 18% had no follow-up sputum examination; 3% were lost to follow-up; and 4% were known to be sputum positive (Table 2). Fifteen state and territorial possessions reported that more than 90% of their patients had negative sputum within 6 months; four states reported that less than half of their patients were known to be sputum negative within 6 months (Table 3).

During 1972-1983, the percentage of patients known to have converted to negative sputum within 6 months of treatment decreased from 88% to 75%. Patients for whom no sputum results were available 6 months after initiation of treatment increased from 6% to 18%. The percentage known to have had positive sputum after 6 months of starting therapy has remained nearly constant at 4% during the 12-year period. From 1972 to 1981, the percentage of patients lost to follow-up increased from 2% to 4%, but has since dropped to 3% (Figure 3). Reported by Div of Tuberculosis Control, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Examination of the sputum of patients with pulmonary tuberculosis at 2- to 4-week intervals until conversion occurs is important for several reasons. It provides objective evidence of the patient's response to therapy. A delayed or absent response may result from patient noncompliance, drug-resistant organisms, prescription error, immunosuppression, or malabsorption of drugs. Failure to detect these problems early, and to adjust the chemotherapy regimen accordingly, may lead to treatment failure and potential transmission of tubercle bacilli to others in the community. Results can also be used to estimate the level of patient infectivity, which permits decisions concerning hospital isolation procedures, the need for supervised therapy, and the investigation and management of patient contacts (1,2).

Periodic bacteriologic examinations are necessary for establishing the length of therapy for patients. CDC and the American Thoracic Society currently recommend that the patient receive isoniazid (INH) and rifampin (RIF) for at least 6 months beyond the time of conversion (the time of the first negative sputum results, after which there are no subsequent positive sputa) or a minimum of 9 months total therapy, whichever is longer (3). An appropriate and a minimum length of treatment can be calculated for those patients for whom the date of conversion is known.

Among patients with uncomplicated pulmonary tuberculosis treated with INH- and RIF-containing regimens, virtually 100% become sputum negative within 6 months if they follow prescribed treatment regimens (4). Because the data reported here include patients treated with regimens other than INH and RIF, as well as patients with drug-resistant organisms or immune-compromising conditions, an overall national conversion rate of 100% within 6 months is not a realistic goal. However, a goal of 95% sputum conversion within 6 months is realistic and was achieved by seven states and territorial possessions in 1983.

The downward trend in the percentage of patients known to have become sputum negative from 1972 through 1983 was accompanied by an increase in the percentage of patients lost to follow-up and for whom no sputum results were available. The number of patients from whom no sputum result was available includes patients the attending physician presumed had converted, but from whom no specimen was obtained to document sputum negativity. Data from four metropolitan-area health departments indicate that some nonhealth department health-care providers either do not routinely obtain sputum specimens to monitor the patient's response to therapy or do not report bacteriologic results to the health department.

Early in the course of treatment, patients with pulmonary tuberculosis should have sputum examinations performed every 2-4 weeks, until sputum negativity on two consecutive cultures is documented. Subsequently, it is not necessary to collect more specimens unless signs and/or symptoms suggest treatment failure or relapse. Without documenting that sputum cultures have become negative, neither the clinician nor the health department can verify a patient's noninfectious status.


  1. CDC. Guidelines for prevention of TB transmission in hospitals. Atlanta, Georgia: U.S. Department of Health, Education, and Welfare, Public Health Service, 1982; HEW publication no. (CDC) 82-8371.

  2. American Thoracic Society/CDC. Control of tuberculosis. Am Rev Respir Dis 1983;128:336-42.

  3. American Thoracic Society/CDC. Treatment of tuberculosis and other mycobacterial diseases. Am Rev Respir Dis 1983;127:790-6.

  4. Fox W. The chemotherapy of pulmonary tuberculosis: a review. Chest 1979;76:785-96.

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