Diagnosis of tuberculosis in sputum negative patients in Dar es Salaam

Objective: To determine diagnostic criteria for tuberculosis among sputum s mear acid fast bacilli negative patients: with chronic cough, based on symp toms, 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 betwe en 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 bacil li (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 a nalysis of all symptoms, signs and laboratory test results, cough of four o r more weeks, haemoptysis, oral candidiasis, chest consolidation, pleural e ffusion, mid zone and upper zone chest x-ray opacities were significantly d ifferent between sputum AAFB negative TB and non TB patients. Discriminant analysis revealed six highly significant variables: Mantoux reaction, pleur al effusion, Kaposl's lesion, cervical lymphadenopathy, matted lymph node, mid zone and upper zone CXR infiltrates. From these variables an equation w as derived to calculate the probability that a sputum smear negative patien t had tuberculosis, Then a scoring system was developed that classified cor rectly 84% of cases of sputum AAFB negative patients into tuberculosis or n on tuberculosis. Conclusion: In sputum smear AAFB negative patient clinically suspected to h ave tuberculosis, Mantoux reaction, cervical lymphadenopathy, matted Lymph nodes, absence of mid lower zone infiltration on CXR and presence of pleura l effusion could be used for presumptive diagnosis, but they would not make a therapeutic trial unnecessary.