Skip Navigation LinksSkip Navigation Links
Centers for Disease Control and Prevention
Safer Healthier People
Blue White
Blue White
bottom curve
CDC Home Search Health Topics A-Z spacer spacer
Blue curve MMWR spacer

Epidemiologic Notes and Reports Bacteriologic Conversion of Sputum among Tuberculosis Patients

By the end of 1981, 83 state and local health departments had submitted to CDC information on bacteriologic conversion for 11,242 patients with sputum-positive pulmonary tuberculosis (by smear or culture or both), who began chemotherapy during 1980. These patients represented about 60% of the sputum-positive pulmonary tuberculosis cases reported in the United States in 1980. Within 3 months of starting treatment, 55.3% had negative sputum. Of the 10,055 patients who had not relocated or died, 77.0% had sputum-negative results within 6 months of starting treatment (Table 1). Eight states (Alabama, Kansas, Kentucky, Nebraska, South Dakota, Utah, Vermont, and Virginia) reported that over 90% of their patients had negative sputum within 6 months; Connecticut and the District of Columbia reported fewer than half became sputum-negative within 6 months (Table 2). Overall, 6 months after starting treatment, 5.4% of the 10,055 patients had positive sputum, 2.6% were lost to supervision, and 14.9% were not known to have had a follow-up sputum examination (Table 2).

Since 1972, a varying number of state and local health departments have submitted similar data to CDC. The number of reporting areas has ranged from a low of 42 in 1972 to a high of 87 in 1979. Over the 9-year period, the percentage of patients known to have converted to negative sputum after 6 months of treatment has fallen from 87.5% to 77.0%. The percentage from whom no sputum result was available has risen from 6.1% to 14.9%. The percentage known to have positive sputum has remained about 5%; and the percentage lost to supervision has risen from 1.7% to 2.6% (Figure 1). The secular trends for 15 individual areas reporting data for each of the 9 years are similar to the trend for all the areas (Figure 2), suggesting that the observed changes are real and do not result from adding areas with different program characteristics to the data base. Reported by Tuberculosis Control Div, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Since 1972, the number of health departments using the bacteriologic conversion of sputum as an indicator of program effectiveness has doubled, suggesting many areas consider it a useful program-evaluation tool. Periodic bacteriologic examination of the sputum of patients with pulmonary tuberculosis is important for several reasons: 1) It provides objective evidence of the patient's response to therapy. Delayed or absent response may be due to 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 will lead to treatment failure and potential transmission of tubercle bacilli. 2) Periodic bacteriologic examination of sputum also estimates the level of patient infectivity, which permits informed decisions to be made about hospital isolation procedures and the investigation and management of patient contacts (1,2). 3) Periodic bacteriologic examination aids in establishing an appropriate length of therapy. For patients on short-course chemotherapy, it is currently recommended that the patient receive isoniazid (INH) and rifampin (RIF) for at least 6 months after sputum conversion (the time of the first negative sputum test, after which there are no subsequent positive sputa), or a minimum of 9 months total therapy, whichever is longer (3). Therefore, the appropriate length of treatment can be calculated for those patients for whom the date of sputum conversion is known.

Among patients with uncomplicated pulmonary tuberculosis treated with INH and RIF, about 95% should become sputum-negative within 3 months if they comply with their treatment regimens (4). Because the data reported above include patients treated with regimens other than INH and RIF, noncompliant patients, and patients with drug-resistant organisms or immune-compromising conditions, a conversion rate of 95% within 3 months cannot realistically be expected. Nevertheless, the reported data indicate a need for improvement. The downward trend since 1972 in the percentage of patients known to have become sputum-negative is compensated for by the rise in the percentage of patients not known to have had a follow-up sputum examination (Figure 1). The number from whom no sputum result was available may include patients whom the attending physician presumed had converted but from whom no specimen was obtained to document sputum negativity. Some areas have indicated that the trend reflects the shift in patient care from health departments to private practitioners, who either do not examine sputum or do not report results to health departments.

The repeated induction of sputa from asymptomatic patients is not recommended merely to supply data for a progress report. After sputum negativity has been established and symptoms have disappeared, no more specimens need be routinely collected unless signs or symptoms or both suggest relapse. Early in the course of treatment, however, sputum examination should be performed frequently, until sputum-negativity is documented. Without negative sputum results, neither the clinician nor the health department can know that a patient has become noninfectious.


  1. CDC. Guidelines for prevention of TB transmission in hospitals. Atlanta U.S. Department of Health, Education, and Welfare Public Health Service, CDC, 1979:HEW Pub. No. CDC 79-8371.

  2. American Thoracic Society. Guidelines for the investigation and management of tuberculosis contacts. Am Rev Respir Dis 1976;114:459-63.

  3. CDC. Guidelines for short-course tuberculosis chemotherapy. MMWR 1980;29:97-100, 105.

  4. Long MW, Snider DE Jr, Farer LS. U.S. Public Health Service Cooperative trial of three rifampin-isoniazid regimens in treatment of pulmonary tuberculosis. Am Rev Respir Dis 1979;119:879-94.

Disclaimer   All MMWR HTML documents published before January 1993 are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to

Page converted: 08/05/98


Safer, Healthier People

Morbidity and Mortality Weekly Report
Centers for Disease Control and Prevention
1600 Clifton Rd, MailStop E-90, Atlanta, GA 30333, U.S.A


Department of Health
and Human Services

This page last reviewed 5/2/01