[Epidemiological study on factors affecting the hospitalization period of patients with active tuberculosis]

We compared the time needed for sputum negative conversion of tubercle bacilli among patients with active tuberculosis to clarify factors affecting the hospitalization period.

We retrospectively reviewed 1260 patients definitely diagnosed as active tuberculosis between Jan. 1996 and Dec. 2003. Smears were examined by fluorescent staining procedure, and cultures were tested by egg-based Ogawa and Kudo-PD solid media. Sputum smears and cultures were examined at least once a month. All patients received standard chemotherapy including isoniazid (INH), rifampicin (RFP), ethambutol hydrochloride (EB) [or streptomycin sulfate (SM)], and pyrazinamide (PZA). Time needed for sputum conversion was defined as the period from the initiation of chemotherapy to the first documented negative smear and culture. Multivariate analysis was performed to document factors that were independently associated with hospitalization period.

Factors correlated with longer conversion time were high amount of bacilli discharge, severe radiographic findings, and drug sensitivity at the initiation of treatment. Patients with bacilli discharge Gaffky 9-10 required 3 months (median) [3.9 months (mean)], and those with culture 3+ required 2 months (median) [2.8 months (mean)] for conversion. Patients with large and widespread cavities, classified as I or II 3 according to the Classification by the Japanese Society for Tuberculosis, required conversion time of 3 months (median) [2.8 months (mean)]. Cases with initial drug resistance to any of the drugs required 2 months (median) [2.2 months (mean)] for conversion. Factors associated with prolongation of hospitalization were the amount of bacilli in sputum at the initiation of chemotherapy, past history of tuberculosis, presence of cavities and size of lesion observed on chest X-ray, drug resistance, and presence of extra-pulmonary lesions. Gender, complication with chronic renal failure, and alcoholism did not affect the hospitalization period.

Patients with huge amount of bacilli discharge, extensive cavitary lesion, or initial drug resistance required more than 2 months for sputum negative conversion. In these cases, hospitalization period shorter than 2 months is inadequate, even if chemotherapy is initiated. For complete eradication of tuberculosis, we must ensure adequate chemotherapy and hospitalization period to eliminate further sources of infection. Our study shows that hospitalization period should be cautiously determined based on the disappearance of bacilli in sputum.