Part I: Organisation and management
laboratory services

Integrated versus specialised services
Before the introduction of effective anti-tuberculosis drugs, the bacteriology of tuberculosis was usually confined to examination of smears at bacteriology departments of general hospitals or at tuberculosis dispensaries and clinics. Culture, guinea pig inoculations and identification of tubercle bacilli were almost exclusively done in laboratories of specialised sanatoria or tuberculosis hospitals.

Following the introduction of anti-tuberculosis chemotherapeutic agents after World War II, patients rapidly became non-infectious and were no longer isolated in sanatoria for long periods of time. Tuberculosis patients were treated in general hospitals as out-patients and tuberculosis bacteriology moved away from specialised laboratories into those of more general pathology departments. Unfortunately, this resulted in sub-optimal methods in some laboratories while others were hampered by a lack of experience and interest. Today it is still not unusual for health care workers to comment on the variation in the quality of technical assistance which they receive from laboratories, and strong arguments sometimes develop for tuberculosis bacteriology to once again become the domain of specialised laboratories.

The obvious advantage of exclusive tuberculosis laboratory services lies in dedication to tuberculosis bacteriology (often lacking in integrated services). Any technique will give better results when it is applied by specially trained workers as their only activity, than by persons who apply it occasionally and as one among many activities. However, the only way in which tuberculosis control can be applied on a community-wide scale in any country is through the general health service and within the framework of primary health care. When a technique (such as microscopy) has to be applied everywhere and over a long period - often permanently - the operational aspects must take precedence over the technological. Peripheral laboratories (and in some countries even regional laboratories) for tuberculosis should, therefore, be integrated within the public health laboratory system. The first aim should be to achieve the operational advantage of "quantity", ie. a complete extension of peripheral laboratory services and full coverage, and then to follow this closely by achieving "quality" through continuous training and supervision.

However,

Extension of tuberculosis laboratory services should not outpace the extension of DOTS coverage in countries

Some of the laboratory techniques used in tuberculosis bacteriology do require complicated and expensive technology as well as equipment that is difficult to maintain. Furthermore, laboratory workers have a well-defined risk of tuberculosis infection if proper precautions are not taken. These arguments favour the establishment of specialised tuberculosis laboratory services at the higher levels of the health service.

Levels of laboratory services
Tuberculosis laboratory services should form part of integrated tuberculosis control programmes, which in turn should form part of overall primary health care programmes of countries. It follows, therefore, that tuberculosis laboratory services should be organised according to the three levels of general health services, ie:

• the peripheral (often district) laboratory
• the intermediate (often regional) laboratory
• the central (often national) laboratory

In terms of technical complexity, the activities performed at each level are different:

Peripheral laboratories should be capable of performing sputum smear microscopy utilising Ziehl-Neelsen (ZN) staining of unconcentrated sputum specimens from tuberculosis suspects. Peripheral laboratories should be fully integrated with primary health care services and could be based at primary health care centres or district hospitals.

Intermediate laboratories should be capable of providing supervision, monitoring, training and quality assurance to peripheral laboratories. Fluorochrome staining of sterilised concentrated specimens in addition to ZN procedures may be done, if dictated as such by the load of specimens. Mycobacterial culture of clinical specimens and differentiation between M. tuberculosis and other mycobacterial species could be performed in regional laboratories. These could be integrated with existing public health laboratories in bigger hospitals or in cities, provided that dedicated tuberculosis bacteriology sections can be identified.

Central laboratories should be at the apex of health laboratory structures and should be capable of performing microscopy (both ZN and fluorescence), mycobacterial culture, drug susceptibility testing and species identification. These laboratories may be separate from public health laboratories and could reside in research institutions or in a country' s principal tuberculosis or public health institution. Aside from the technical activities pertaining to these reference centres, national laboratories should provide training for laboratory staff, perform quality assurance and proficiency testing, exercise surveillance of primary and acquired tuberculosis drug resistance and participate in epidemiological and operational research.

In the early phases of development of a laboratory service for tuberculosis in a high prevalence country the most economical and efficient arrangement is as follows:

1. Establishment of ZN microscopy in small, multi-purpose public health laboratories. Caution is, however, necessary when establishing peripheral microscopy sites, since a direct relationship exists between workload, number of microscopists required and the quality of microscopy performed in these small laboratories. The maximum number of ZN smears examined per microscopist per day should not exceed 20. If more examinations are attempted, visual fatigue will lead to a deterioration of reading quality. On the other hand, proficiency in reading ZN smears can only be maintained by examining at least 10 to 15 ZN smears per week, ie. a minimum of 2-3 examinations per day.

   One microscopy centre per 100 000 population is usually sufficient to attain the target of 2-20 ZN smears per day.

   In densely-populated areas fewer laboratories would be required if transport and communication mechanisms could be improved, while in remote and sparsely populated areas more laboratories may be needed. Therefore, in planning microscopy services, careful consideration should be given to the following aspects:

   • location and utilisation of existing services (if any)
   • population distribution
   • transport facilities
   • expected workload based on the recommendations for case detection, diagnosis and monitoring of treatment

   Annex 1 provides an example of how to assess whether the number of microscopy centres in a country is adequate.

2. Establishment of fluorescence microscopy at regional laboratories where more than 100 smears are examined per day. Since low magnification is used, screening of a smear can be up to five times faster. Fluorescence microscopy requires much more expertise and experience and the capital cost and running expenditure are considerable. Also, it is necessary to retain Ziehl-Neelsen microscopy to confirm positive smears found by fluorescence microscopy, especially if microscopists are inexperienced with regard to fluorescence microscopy, and for training and quality assurance of the peripheral laboratories.
3. One fluorescent microscopy centre per 500 000 to one million population is usually sufficient. However, this is much more strongly dictated by the daily case load than by the actual population covered.
4. Establishment of tuberculosis culture facilities at regional or central level, to cover 500 000 to one million population. Specimens from peripheral health centres should reach the culture laboratory within five days. Since the capital cost of equipment and its satisfactory maintenance are much larger items of expenditure than staff salaries, it is usually not cost-effective to use highly simplified culture procedures which are less efficient than slightly more complicated methods. For example, culture methods employing a centrifuge are more efficient than simple decontamination and culture of sputum directly onto medium. The additional cost of a centrifuge and the time taken in processing the specimen is very small compared to the total running cost of the laboratory.
5. Establishment of a central reference laboratory at national or regional level, to cover 10 million or more population. In small countries one central reference laboratory should be established, even if the population is below 5 million. In large countries, several such laboratories may be established, but one of these should be designated the national reference laboratory.
6. As bacteriological services extend and as health care workers begin to utilise bacteriological methods in preference to radiography, there will be an increasing demand for smear and culture examinations. The most economical way is then to establish fluorochrome microscopy in busier microscopy centres and to increase the number of culture facilities.

Functions and responsibilities of peripheral, intermediate and central laboratories
Tuberculosis laboratory services cover various activities, which differ from country to country and even from region to region within a country. These can be summarised as follows:

• detection of acid-fast bacilli by microscopy
• bacteriological culture of clinical specimens for mycobacteria
• identification of mycobacterial species
• performance of drug susceptibility tests
• performance of quality assurance and proficiency testing
• consultation with health care workers on the diagnosis and management of tuberculosis
• collection and analysis of laboratory data for epidemiological purposes
• teaching and training of laboratory staff
• participation in epidemiological and operational research

Obviously, not all of these activities can or should be carried out by every laboratory. The functions and responsibilities of the various levels of laboratory services can be summarised as follows:

PERIPHERAL LEVEL
Technical

• preparation and staining of smears
• ZN microscopy and recording of results
• internal quality control

Administrative

• receipt of specimens and despatch of results
• cleaning and maintenance of equipment
• maintenance of laboratory register
• management of reagents and laboratory supplies

INTERMEDIATE LEVEL
All the functions of the peripheral level, plus:

Technical

• fluorescence microscopy (optional)
• digestion and decontamination of specimens
• culture and identification of M. tuberculosis
• preparation and distribution of reagents for microscopy in peripheral laboratories

Managerial

• training of microscopists
• support to and supervision of peripheral staff with respect to microscopy
• external quality improvement and proficiency testing of microscopy at peripheral laboratories

CENTRAL LEVEL
All the functions of the intermediate level, plus:

Technical

• drug susceptibility testing of M. tuberculosis isolates
• identification of mycobacteria other than M. tuberculosis

Administrative

• technical control of and repair services for laboratory equipment
• updating and dissemination of manuals on bacteriological methods for diagnosing tuberculosis
• development and dissemination of guidelines on care and maintenance of microscopes and other equipment used in tuberculosis bacteriology
• development and dissemination of guidelines on tuberculosis laboratory supervision and quality assurance
• collaboration with the central level of the National Tuberculosis Programme in defining technical specifications for equipment, reagents and other materials used in bacteriological investigations, and in estimating laboratory materials and equipment requirements for the Programme budget

Managerial

• training of intermediate laboratory staff in bacteriological techniques and support activities, ie. training, supervision, quality assurance, safety measures and equipment maintenance
• supervision of intermediate laboratories regarding bacteriological methods and their support (particularly training and supervision) to the peripheral laboratories
• quality assurance of microscopy and culture performed at intermediate laboratories

Research and surveillance

• organization of surveillance of primary and acquired mycobacterial drug resistance
• operational and applied research relating to the laboratory network, co-ordinated with the requirements and needs of National Tuberculosis Programmes.