TB LABORATORY SERVICES AND ITS QUALITY CONTROL
Ms. Akiko FUJIKI
The Research Institute of Tuberculosis, JATA
TB LABORATORY SERVICES
WHO estimated that 1/3 of the World's population are infected with tuberculosis. An estimated 88 million new cases of TB will occur on third millennium and approximately 30 million people are to die of the disease. Based on this background, WHO advocated DOTS (Directly Observed Treatnment, Short Course) Strategy and stressed the importance of sputum smear microscopy, and quality control on sputum smear examination as well.
Tuberculosis is an infectious disease caused by TB bacilli. Thus the object of tuberculosis control is to break the chain of transmission of infection and it is clearly stated as follows by WHO 9th report, 1974;
"The object of tuberculosis control is to break the chain of transmission of infection. This can be achieved by detecting the source of infection as early as possible and rendering them noninfectious by chemotherapy. Transmission is maintained in the community particularly by subjects whose sputum is so heavily positive that tubercle bacilli can be detected by smear microscopy."
The priority of tuberculosis control is smear positive cases since they are the greatest risk to the community and WHO recommends that the diagnosis of tuberculosis is based on direct sputum smear microscopy.
Direct sputum smear microscopy is a reliable, quick, less expensive and feasible tool for the diagnosis of both pulmonary smear positive tuberculosis and pulmonary smear negative tuberculosis. Currently, there is no other diagnostic tool available, which could be implemented, nationwide at reasonable cost in low- and middle-income countries. Therefore, direct sputum smear microscopy should be carried out with the utmost care at the well-established laboratories. Well establishment of laboratory services is one of the key operations of National TB control Program and laboratory services are not only TB microscopy but also laboratory network and quality control activities.
QUALITY CONTROL OF SPUTUM SMEAR EXAMINATION
Here, experience of quality control for sputum smear examination is introduced.
JICA Philippines TB control project has a major component to strengthen the quality of sputum smear examination since 1994 in the Regions 4 and 7 in the Philippines. Cebu City of Region 7 with 700,000 population has a Reference Laboratory and 5 peripheral laboratories. The quality control system has been developed since 1997 in Cebu City as a model approach.
The activities of TB smear examination in Cebu City were analyzed with the results of quality control reported from January 1997 to December 1998 in the 5 peripheral laboratories. Various technical aspects of sputum smear examination and management of laboratory activities were discussed.
Total smear slides checked for quality control in 1997 and 1998 were 4,775 and 4,249 respectively. Comparing the results from first quarter of 1997 and the last quarter of 1998, the improvement was observed in all assessment points of smear preparation; namely sputum quality, staining smear cleanness, smear area size, smear thickness and evenness. In particular, remarkable improvement was observed in staining from 56.2% to 96.0% and in smear thickness from 48% to 91 .2%, which were almost doubled in each assessment point of smear preparation. The marked improvement was noted within 6 months after quality control started. It is suggested that at least 6 months are required and frequent supervisory visit should be made to strengthen the smear preparation. The reading ability of acid-fast bacilli (AFB) was improved and considered to be acceptable and reliable as well. Overall agreement of the reading grade was 81.1 % in the first quarter of 1997 and 99.1% in the last quarter of 1998. False (+) and false (-) were from 1.9% to 0.2% and from 2.9% to 0.7% respectively. Most of the false readings occurred at a reading of (1+) or 1-2AFB in 300 visual fields.
The factors identified for contributing to the improvement are: standardized equipment and regular provision of reagents supply, distribution of binocular microscopes to all laboratories, expansion and maintenance of proper size of the laboratory, and frequent supervisory visits made with a strong leadership by the supervisor.
DOTS will be successful with good quality of sputum smear examination since case detection and cure rate depend on the result of smear microscopy.
