Evaluation of Fluorescence Microcopy and Indirect ELISA in the Diagnosis of Pulmonary Tuberculosis in Khartoum State

Abstract

Tuberculosis remains a major health problem in the Sudan and a leading cause of morbidity and mortality . Early diagnosis and correct treatment are the mainstay for the control of the disease. The present study aimed to evaluate fluorescence microscopy (FM) in the detection of M.tuberculosis in sputum and to compare the results to light microscopy using ZN stained smear and culture in addition to a serological method (ELISA using 38kd antigen). Another aim of the study was to determine the sensitivity and specificity of ELISA and to compare the results with those obtained by direct microscopy (light, and fluorescent). A descriptive study was carried out in 233 patients with clinical features suggestive of TB (fever, chronic cough, mucopurulent sputum, loss of weight, night sweat, and haemoptysis), who reported to Abou-Anja Chest Hospital (Omdurman) between the period from June 2002 up to October 2003, were included. Sputum samples were collected from all the patients and studied by bacteriological methods including FM, ZN and culture. In addition, a venous blood sample (5ml ) was obtained from each patient ; serum was separated and tested with ELISA for the detection of IgG antibodies against 38kd antigen .Blood samples were also collected from healthy controls at the Blood Bank , Khartoum Teaching Hospital. 81(35%)cases were positive by ZN method ,while the FM method detected 93(40 %) positive cases. The culture technique showed 75(32 %) positive cases; in 69 (92%) of those cases the growth of 6 M.tuberculosis was confirmed by growing the organism on TCH media. In the other 6 (8%) culture positive samples, growth similar to M.bovis and M.africanum was observed but more investigations were needed to determine the species. As compared to culture and ZN the FM showed a sensitivity of 80.6% and 75.3%, respectively. Statistical analysis showed that FM was more sensitive than ZN and culture (P= 0.0001). The ELlSA was positive in 103 (44.2%) of the studied cases. The sensitivity of the test - as compared to ZN, FM, and culture -was 48.5%, 49.5% and 42.7, respectively . The ELISA was less sensitive than ZN staining method (P=0.0001), FM (P=0.01) culture (P=0.003). The specificity of ELISA was 82% as compared to apparently health controls. However, in 53 of the ELISA positive cases who were negative by ZN, the culture was positive in 8 cases. In addition , the culture was positive in 5 of the 52 cases, who were ELISA positive but FM negative. In view of the results obtained in the present study it can be concluded that FM is more sensitive than ZN staining method and culture in the detection of M.tuberculosis in sputum samples for the diagnosis of PTB . Accordingly the FM is recommended to be included in the routine diagnosis of PTB in ZN stained smear negative cases. In spite of the low sensitivity of ELISA the test can still be useful in the diagnosis of TB in some cases in whom bacteriological diagnosis can not be confirmed. The test may also be helpful in the diagnosis of the disease in patients in whom sputum sample cannot be obtained.