Smear-negative pulmonary tuberculosis

Abstract

Diagnostic difficulties arise when sputum smears are negative for acid-fast bacilli in tuberculin-positive patients with compatible symptoms and chest radiographs for tuberculosis. Many of these smear-negative patients yield positive cultures for M tuberculosis, whereas others remain culturally negative. Several studies have shown that many smear-negative/culture-negative patients will develop bacteriologically positive disease later. Often, physicians are unable to decide whether to initiate chemotherapy or to wait for the culture results. Also, if treatment is initiated in smear negative patients, what should be the drug regimen and duration of therapy. A positive smear signifies a very large bacterial population in the lung lesions whereas several negative smears suggest a smaller bacterial load. Such smear-negative cases do not require the same intensity and duration of treatment as smear-positive cases. Therapy should be initiated for tuberculosis after other causes for abnormal chest x-ray have been excluded. However, duration of therapy may be shortened in these cases. The British Medical Research Council (BMRC) study has shown that intensive treatment of smear-negative/culture-positive disease with streptomycin (SM), isoniazid (INH), rifampin (RIF), and pyrazinamide (PZA) for 4 months was uniformly successful. This regimen is routinely recommended in Hong Kong. Because primary drug resistance is low (< 3%) in Arkansas, we treated these cases with INH and RIF for 6 months with good results. This is now a routine drug regimen. For smear-negative/culture-negative cases, the BMRC study has shown that daily or thrice weekly treatment with SM, INH, RIF, and PZA for 4 months is effective.(ABSTRACT TRUNCATED AT 250 WORDS)