Guidelines on the Prevention and Control of Tuberculosis in Ireland

<strong>Guidelines</strong> on the Prevention and Control of Tuberculosis in Ireland 2010HSE/HPSC4. Laboratory Diagnosis of Tuberculosis4.1 Role and Goals of the Modern TB LaboratoryThe microbiology laboratory makes a key contribution to TB control in terms of diagnosis, infectionprevention and control and management of the disease. The detection and isolation of mycobacteria,identification of the mycobacterial species or complex isolated and the determination of susceptibilities ofthe organism to anti-mycobacterial drugs are key functions of a modern TB laboratory. 110 The gold standardfor diagnosing active disease is by microbiological identification of TB by culture. Molecular typing ofisolates contributes significantly to understanding the epidemiology of TB. Population based molecularepidemiology studies have been used to evaluate TB control efforts, providing insights into transmissiondynamics, enhancing contact tracing and aiding the detection of laboratory cross-contamination. 111 Therole and importance of skilled and experienced staff cannot be over emphasised. 112In 1993, WHO declared TB a global emergency in response to an increase in cases after nearly a century ofdecline. Targets for achieving improved control were developed which involved diagnosing a minimum of70% of individuals with sputum smear positive TB and curing at least 85%. In Ireland, important legislativechanges have occurred since the publication of the 1996 TB guidelines. 113 In 2003, the Infectious DiseasesRegulations 1981 were amended by the Infectious Disease (Amendment) (No. 3) Regulations 2003 (S.I.No. 707 of 2003), stating that a clinical director of a diagnostic laboratory shall have regard to the casedefinitions for notification of infectious diseases. 21 The DPH or designated medical officer should benotified of the identification of a TB case ideally within one working day.Recommendation:It is a mandatory requirement for clinical directors of diagnostic laboratories to notify cases ofactive TB disease to the medical officer of health (director of public health or designate).Culture is necessary to achieve the “gold standard” for the diagnosis of active tuberculosisdisease.Levels of serviceBefore offering mycobacteriology services, each laboratory should assess the capacity and capability of thelevel of services performed. Clinical laboratories offering a mycobacteriology service are divided into threemajor categories of service (table 4.1). This follows recommendations by CDC and the American ThoracicSociety (ATS) stating that laboratories interpreting acid fast stained smears should process at least 10-15specimens per week to maintain proficiency and those processing specimens for culture should handle aminimum of approximately 20 specimens per week. 114-117 The majority of laboratories in Ireland are Level 2.Table 4.1: Levels of service for diagnostic microbiology laboratoriesLaboratoryservice levelLevel 1Level 2Collection and transport of specimens; preparation and examination of smears for AFB.Procedures of level 1, plus procedures for the isolation of Mycobacterium species.Identification of M. tuberculosis complex may or may not be performed.Level 3All procedures in level 2, plus identification of all species of mycobacteria. The determinationof drug susceptibility for all Mycobacterium species and typing of M. tuberculosis complexshould be performed at level 3.-44-