Two sputum samples are enough to diagnose pulmonary tuberculosis
To determine the contagiousness and isolation of Mycobacterium tuberculosis in patients with suspected pulmonary tuberculosis, two negative sputum smears for acid-resistant bacteria are sufficient.
To determine the contagiousness and isolation of Mycobacterium tuberculosis in patients with suspected pulmonary tuberculosis, two sputum smears negative for acid-resistant bacteria (CUB) are sufficient.
As various epidemiological studies have shown, patients with pulmonary tuberculosis, for whom consecutive samples of sputum during a bacterioscopic examination on a CUB, are negative, are less contagious than "positive" patients. However, data indicating a number of negative sputum smear microscopy results as adequate to assess the infectivity of these patients are insufficient.
Researchers analyzed 122 cases of pulmonary tuberculosis in Texas in 1998 and 1999. In all cases, the patients presented bacteriologically confirmed tuberculosis (sputum culture), as well as negative results on the KUB microscopy of sputum smears during infectious period, which meant the time interval between the onset of cough and / or hemoptysis up to 14 days after the appointment of effective treatment, at least 2 drugs with confirmed activity against mycobacteria in vitro or until the patient's death or change of residence.
Patients were divided into 2 groups: group A consisted of patients with only 1 or 2 collected and fully successful microbiological studies of sputum, and group B consisted of patients with at least 3 collected and successful microbiological studies of sputum or sputum obtained by bronchoscopy. All patients were interviewed for possible contacts during the infectious period. These contacts were divided into 2 groups: close contacts (with people living in the same house as the patient) and contacts other than close. In 122 patients, the number of contacts was 1577, of which 1181 were fully examined by a tuberculin skin test. The average age of the examined patients who contacted the patients was 26 years. The tuberculin skin test results were positive in 39% of the close contacts and in 22% of the other contacts. Researchers identified a case index and characteristics for contacts associated with the transmission of tuberculosis.
The predisposing factors (predictors) independent of positive results were the male and younger age of TB patients, and for those in contact with the patients, belong to the Latin American ethnic group. For youth who were in contact with patients, the positive skin test results were less characteristic. Regardless of the group in which the case of tuberculosis (A or B) was noted, it was not an independent predictor of the transmission of tuberculosis. In the group with at least three sputum samples obtained, bacteriological examination of the first two sputum samples gave 90% of all positive results.
Researchers believe that two negative sputum samples microscopically on a CUB are sufficient to assess contagiousness and to isolate mycobacterium tuberculosis in patients with pulmonary tuberculosis. For the third smear for microscopy, this approach may be acceptable if the doctor wishes to perform the maximum range of diagnostic measures before deciding to conduct more invasive studies (bronchoscopy or biopsy of lung tissue).
These results indirectly confirm the recommendations that patients with two negative results of microscopic examination of sputum samples and receiving effective treatment should not require additional respiratory isolation, thus reducing the period of isolation would reduce the economic costs of an inpatient and possibly reduce the number of side effects.