RATIONALE FOR SURVEILLANCE
Anti-tuberculous drug resistance occurs when a strain of Mycobacterium tuberculosis isolate is resistant to one or more antimicrobial agents as evidenced by internationally recommended methods for susceptibility tests (e.g., the economic variant of the proportion method, using Löwenstein-Jensen medium). The absolute concentration, resistance ratio, and other standardized methods may be used.
Primary drug resistance is defined as the presence of resistant strains of M. tuberculosis in a patient who, in response to direct questioning, denies having had any prior anti-tuberculous treatment or for whom, in countries were adequate documentation exists, no documented evidence of such a history is found.
Acquired drug resistance is defined as the presence of resistant strains of M. tuberculosis in a patient who, in response to direct questioning, admits having had prior anti-tuberculous treatment or for whom, in countries were adequate documentation exists, documented evidence of such a history is found.
RECOMMENDED TYPES OF SURVEILLANCE
Three main principles must be followed:
1. Use of a data collection system (based on standard registers) for all tuberculosis patients, designed in such a way that new patients are distinguished from those previously treated. National Tuberculosis Programmes using the WHO tuberculosis control strategy adopt a recording and reporting system which allows this kind of differentiation.
2. Use of laboratory methods internationally recommended for susceptibility testing. A country should have no more than one national reference laboratory (NRL) to which diagnostic centres send the sputum (with the exception of very large countries). The National Reference Laboratory should be linked to an international laboratory by strain exchange to ensure quality control.
3. Adequate sampling strategies must ensure the representativeness of the country or area to be surveyed.
In general, countries can choose between routine surveillance and ad hoc surveys at regular intervals (3-5 years) according to the availability of resources, logistics, and to other operational considerations.
RECOMMENDED MINIMUM DATA ELEMENTS
Peripheral level (diagnostic centres)
• Patient identifier, age, sex, specimen date, history of previous treatment, other data (nationality, HIV status if known). Only patient with positive sputum smear(s) should be enrolled
National Reference Laboratory
• Anti-tuberculous drug susceptibility test results Central
• Data from the diagnostic centres and from the National Reference Laboratory should be matched and analysed by a coordinating team
RECOMMENDED DATA ANALYSIS, PRESENTATION, REPORTS
Peripheral level (diagnostic centres)
• The data should be tabulated at regular intervals by the diagnostic centres and the National Reference Laboratory, using standard forms, or be extracted from routine registers
• Based on the information provided by the diagnostic centres, the national coordinating team must make regular reports to the heads of the National Tuberculosis Programme and the reference laboratory
• Data analysis, by computer whenever feasible (WHO has developed a software for data entry and analysis; see Special Aspects)
• Analysis on a yearly basis for routine surveillance or at the end of ad hoc surveys
• Data must be aggregated by level of resistance to each single drug and each single combination of drugs as well as between primary and acquired resistance
• Stratification of data by age, sex, etc.; trend analysis may be undertaken as and when needed
PRINCIPAL USES OF DATA FOR DECISION-MAKING
• Monitor levels and trends of anti-tuberculous drug resistance prevalence as an indicator of the effectiveness of tuberculosis control efforts
• Identify outbreaks of multi-drug resistance in certain settings
• Provide feedback to those regions or areas which participated in region-representative surveys
• Under special circumstances, review the policy of tuberculosis case management
National quality assurance programmes to assure that the performance of each National Reference Laboratory is monitored by an international laboratory network.
Reporting to WHO for international comparison of performance.
WHO has set up a global network of supra-national reference laboratories (SRL) which are responsible for quality control in various countries. In addition, they exchange strains amongst themselves. This quality assurance allows for the international comparison of survey results.
WHO has developed a simple software programme (SDRTB-2) based on EPI-Info for entering and analysing data from surveys. It can produce summary tables with the prevalence of drug resistance for each drug, analysed from different perspectives. The software is available free of charge from WHO.
See Regional Communicable Disease contacts on section "Communicable disease contacts in Regional Offices".
Headquarters: 20, Avenue Appia, CH-1211 Geneva 27 Switzerland
Communicable Disease Surveillance and Response (CSR)
E-mail address: Surveillancekit@who.ch
Tel: (41) 22 791 2708
Fax: (41) 22 791 4878