Diagnostic yield of repeated smear microscopy examinations among patients suspected of pulmonary TB in Shandong province of China.

OBJECTIVES: To analyse the yield of five repeated smear microscopy examinations for the diagnosis of smear-positive pulmonary tuberculosis (TB). METHODS: Patients with respiratory symptoms and abnormal chest X-rays provided five spontaneous sputum samples for acid-fast bacilli (AFB) smear microscopy in one of nine county laboratories. RESULTS: Of 9302 patients with respiratory symptoms and abnormal X-rays, 6437 (69%) had at least one smear-positive sputum. Of these, 84.5% were diagnosed on the first smear, 96.7% on the first two smears, and 99.9% on the first three sputum smears. The fourth and fifth sputum smears yielded only seven additional cases (0.1%). CONCLUSIONS: Smear microscopy examination of two spontaneous sputum specimens is the most efficient, and three sputum smear examinations provide a diagnosis in almost all cases.