ABSTRACT
<b><big>Introduction</big></b><br>Tuberculosis is a major health problem in Lusaka, Zambia, where 16% of the people of productive age was infected with HIV. DOTS coverage is 100% with 81% case detection and 73% cure rate.Following the spread of HIV infection, the number of tuberculosis patients has been increasing. Within this context, the HIV/AIDS and TB Control Project established a model external quality assessment (EQA) system for AFB microscopy service at peripheral laboratories.This study aims to show importance of EQA in quality NTP laboratory system.<br><b><big>Methods</big></b><br>All 22 diagnostic centers in Lusaka during the period from July 2003 to September 2005 were evaluated following internationally recognized guidelines. Sample slides were taken randomly from among slides read at peripheral diagnostic centers and were blindly rechecked by controllers at the quality assurance (QA) center. Quality of smear preparation was also assessed. <br><b><big>Results and Discussions</big></b><br>Between 2003 and 2005, major reading errors (discrepancy: two reading scales and over) found by controllers decreased from 5% of sample slides to 0.7%, and minor errors (one scale discrepancy) from 3.4% to 0.3%. The number of diagnostic centers without any errors was only 3 at the beginning of study and this number increased to 17 at the end. Quality of smear preparation such as thickness, size and evenness also improved based on international standards. These results highlighted the effectiveness of the quality assurance system (blinded rechecking of sample slides and effective feedback with frequent visits to peripheral diagnostic centers) in terms of maintaining the proficiency of AFB microscopy service. EQA system should be expanded in the areas where both HIV and TB prevalence is high. The effective implementation of EQA service in the NTP is the essential factor for the success of DOTS strategy and may contribute ultimately to prevent new tuberculosis infection among persons, including HIV-infected.