Quality control of sputum microscopic examinations for acid fast bacilli in southern Ethiopia

Background: There has been an ongoing effort to strengthen the acid-fast bacilli (AFB) diagnostic laboratory network in the Southern Region of Ethiopia, and quality control has been initiated as part of this effort. Objective: To evaluate the level of agreement in the readings of sputum smears for AFB between the peripheral diagnostic centers and the reference laboratories. Methods: Blinded rechecking of routine slides collected from the peripheral diagnostic laboratories was undertaken in nine zones of the southern Ethiopian region between October 2000 and June 2002. Results: Two thousand two hundred and nine slides, 54% of which were positive and 46% of which were negative slides, were collected from the peripheral diagnostic centes. Overall, false reading was 3.2% and the overall agreement was 96.8%. Among the 95 discordant slides that were re-examined at the central reference laboratory, 74% were found to be in agreement with the regional laboratory readings while 26% were in agreement with the peripheral readings. Nine zones participated in the quality control activity in 2000, six in 2001 and three in 2002. Conclusion: Good agreement was recorded in the readings of AFB among the peripheral and reference laboratories. However, the false positive reading of 3.2% exceeds the recommended cut-off point of 2%. The number of zones participating decreased from time to time, and there seems to be an urgent need to re-vitalise the quality control initiative. Regular on the job training of the peripheral laboratory staff together with supportive supervision would help improve their performance. [Ethiop.J.Health Dev.2005;19(2):104-108] Introduction Case finding through sputum microscopy is one of the five elements of the directly observed therapy, short course (DOTS) strategythe WHO strategy for the management of tuberculosis (TB) (1). Thus, TB control requires a functional laboratory set-up with quality diagnostic services and a trained diagnostician and a microscopist (2). However, the performance of such laboratories depends on continuous monitoring and quality improvement mechanisms put in place (3). The principal objective of external quality assessment (EQA) is to standardise sputum microscopy for the detection of infectious TB cases across the peripheral diagnostic centers and to validate the reported acid-fast bacilli (AFB) microscopy results from these centers. The National Tuberculosis and Leprosy Control Programme (TLCP) manual for laboratory technicians recommends the rechecking of a sample of routine slides as a method of ensuring the quality of diagnosis and classification of TB patients within the health services (4). The aim of this study was to evaluate the performance of sputum microscopic examinations in the peripheral laboratories of the SNNPRS. Methods In the Southern Nations, Nationalities and Peoples’ Regional State (SNNPRS), 167 health facilities are engaged in the diagnosis of TB (5). Over the past seven years, efforts have been made to strengthen the AFB laboratory network in the region. In addition to the provision of microscopes and laboratory supplies to the diagnostic laboratories, a quality control unit was established within the regional reference laboratory in Awassa, the regional capital. As a result, there has been an ongoing quality control of Ziehl-Neelsen (ZN) stained slides collected on a quarterly basis from the peripheral laboratories by the zonal and woreda (district) TLCP coordinators. Patients The main source of data for this cross-sectional study was the quality control register at the regional TLCP office. The ZN stained slides that were collected for quality control from the peripheral diagnostic centers within the region from October 2000 through June 2002 formed the study units. Variables such as sputum smear results in the peripheral diagnostic centers versus the regional and national reference laboratories, the proportion of positive slides, and the consistency of the quality control activities were investigated. Methods The procedures employed for the quality control were in line with the recommendations of the National TLCP (2). In brief, the peripheral laboratories retained all positive slides and an equal number of negative slides were kept in dark places until the Zonal TLCP co-ordinators collected the required number of slides. The number of slides to be collected was determined based on the number of smear positive slides seen in the same quarter. Zonal TLCP co-ordinators submitted the collected slides Quality control of sputum microscopic examinations for Acid Fast Bacilli in Southern Ethiopia 105 Ethiop.J.Health Dev. 2005;19(2) to the regional programme co-ordinator with the results filled in a specially designed form. The regional TLCP co-ordinator filled out slide numbers in a new set of forms without the results, and submitted the slides and the forms to the regional reference laboratory. The laboratory technicians in the reference laboratory examined the slides and reported the results to the regional TB program unit. The microscopists in the regional laboratory did not observe the initial results of the smears at the peripheral diagnostic centers. The regional TLCP coordinator compared the results of the peripheral laboratories against the regional reference laboratory and sent out all discordant slides to the national reference laboratory for re-reading (4,6). The regional TLCP co-ordinator maintained the results of the peripheral as well as the regional and central laboratory readings. Feedback on the smearing and staining quality together with the final AFB result at the reference laboratory was sent regularly to the peripheral diagnostic laboratories. In case of agreement between the peripheral and the regional laboratory readings, the regional laboratory results were taken as final results. Slides with discordant readings were re-read at the central reference laboratory (6), and the results from the central reference laboratory were considered as final results. The sensitivity, specificity, as well as the positive (PPV) and negative predictive values (NPV) of the peripheral readings were calculated against the final readings of the reference laboratories as a gold standard. Statistics and data analysis Data were analysed using the Statistical Package for Social Sciences (SPSS) 11.0 (7) software. In this study, discordant slides were defined as positive slides read as negative or vice versa, as the positive slides were not quantified (graded) either at the peripheral or regional laboratories. Sensitivity, specificity, predictive values, and proportions of false readings were compared using the test and 95% confidence intervals for proportions. The level of agreement among various diagnostic levels was measured using Kappa. The level of significance was set at 5%. Results Two thousand and two hundred nine slides were collected for checking quality and from the peripheral diagnostic centers in nine zones of the southern region. A median of 257 (ranging from 17 to 475) slides were collected from each zone. Fifty four percent (1,184) of the collected slides were positive at the peripheral diagnostic centers and 46% (1,025) were negative. Table 1 shows the number of slides collected each year and the proportion of positive slides. The number of zones participating in EQA decreased from nine in 2000 to 6 in 2001 and to three in 2002. Table 1: Zones that participated in the External Quality Assessment and the number of slides collected each year, southern Ethiopia 2000-2002 Slides collected, n (% positive) Zone