Diagnosis of tuberculosis in sputum negative patients in Dar es Salaam.

Objective: To determine diagnostic criteria for tuberculosis among sputum smear acid fast bacilli negative patients: with chronic cough, based on symptoms, signs and simple laboratory tests, Design: A two-month prospective follow up study. Setting: Muhimbili Medical Centre, Dar es Salaam, Tanzania, Subjects: One hundred and seventy eight consecutive patients admitted between Ist November, 1994 and 31st March, 1995 with chronic productive cough. Main outcome measures: Sputum smear acid fast bacilli (AAFB) negative with TB, discriminating ability of clinical and laboratory parameters, Results: Forty three (24.2%) were sputum smear positive for acid fast bacilli (AAFB), In 90 (50.6%) patients, AAFB could be isolated in specimen other than sputum and in 45 (25.3%) no AAFB could be isolated. In a univariate analysis of all symptoms, signs and laboratory test results, cough of four or more weeks, haemoptysis, oral candidiasis, chest consolidation, pleural effusion, mid zone and upper zone chest x-ray opacities were significantly different between sputum AAFB negative TB and non TB patients. Discriminant analysis revealed six highly significant variables: Mantoux reaction, pleural effusion, Kaposl's lesion, cervical lymphadenopathy, matted lymph node, mid zone and upper zone CXR infiltrates. From these variables an equation was derived to calculate the probability that a sputum smear negative patient had tuberculosis, Then a scoring system was developed that classified correctly 84% of cases of sputum AAFB negative patients into tuberculosis or non tuberculosis. Conclusion: In sputum smear AAFB negative patient clinically suspected to have tuberculosis, Mantoux reaction, cervical lymphadenopathy, matted Lymph nodes, absence of mid lower zone infiltration on CXR and presence of pleural effusion could be used for presumptive diagnosis, but they would not make a therapeutic trial unnecessary.