CDST_LT: TB laboratory classification

Based on 2012 WHO expert group recommendations, TB labs can be classified into three types based on their levels of procedural risk: 

1. Low TB risk
2. Moderate TB risk
3. High TB risk (TB Containment Laboratory)

• Recommendations based on minimum requirements needed to limit or reduce risks of infection in laboratories for carrying out specific procedures.
• Additional measures may be deemed necessary following a site-specific risk assessment.

Based on the operational and diagnostic methods adopted, the laboratories can be classified as:

• The Designated Microscopy Centers (for microscopy only)
• The Nucleic Acid Amplification Testing (NAAT) Laboratories or the Molecular Test Laboratories
• The Culture and Drug Sesitivity Testing (C&DST) Laboratories or the Phenotypic Laboratories

Resources

• GLI LC Training Module on Biosafety, slide no. 30.
• WHO TB Lab Biosafety Manual, 2012.

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Depending on the procedural risk in the TB lab, the lab is classified into low, moderate and high-risk categories.

Low-risk TB laboratories work on sputum specimens for:

1. Direct Acid-fast Bacilli (AFB) smear microscopy
2. Cartridge-based Nucleic Acid Amplification Test (CBNAAT)/ Truenat

Figure 1: Procedures Conducted in a Low-Risk TB Lab

• Procedures that involve direct microscopy or killing of the mycobacteria before microscopy are taken up in these labs.
• These labs have a low risk of generating infectious aerosols from specimens and a low concentration of infectious particles.

Features and Essential Minimum Biosafety Measures of Low-risk TB Labs

1. Space requirements  

• Bench spaces should be separated from areas used to receive specimens and administrative areas used for paperwork and telephones.
• Ensure adequate ventilation; it is important to maintain natural or mechanical, directional airflow with 6-12 air changes per hour (ACH). Workstations are optional solutions.

2. Procedural requirements

To minimize the generation of aerosols:

• Carefully open specimen containers.
• Air-dry smears and use a flame to fix them.
• Use disposable wooden sticks or transfer loops.

For the handling of leaking specimen containers: Discard and request a fresh sample.

3. Personal Protective Equipment (PPE) requirements

• Protective laboratory coats should be worn at all times in the laboratory.
• Gloves must be worn for all procedures that involve direct contact with potentially infectious materials.
• Gloves should not be reused.
• Staff should always wash their hands before leaving the laboratory.
• Respirators are optional.

Figure 2: Challenges in a Low-risk TB Lab that Increase the Risk of Infection

Resources

• GLI LC Training Module on Biosafety.
• TB Lab Biosafety Manual, WHO.

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Moderate-risk TB Laboratories can:  

1. Process specimens for inoculation on primary solid-culture media 
2. Perform direct line-probe assays and direct Drug Sensitivity Testing (DST)

Essential Minimum Biosafety Measures 

• Biological Safety Cabinets (BSCs): Class I or II
• Ventilation: 6-12 ACH
• Personal Protective Equipment: Laboratory gowns and gloves 
• Laboratory design: Restricted traffic area
• Decontamination and waste disposal
• Procedures optimized for minimizing the generation of aerosols

Challenges of Moderate-risk TB Laboratories   

• Staff may work in areas with poor ventilation and/ or poor illumination. 
• BSCs may be poorly maintained and not certified or not be properly ducted.
• Careless manipulation of specimens may lead to aerosolization.
• Specimen containers may break or leak during centrifuging.
• Adequate warnings of biohazards may be lacking, and information on who should be contacted during an emergency may be inadequate.
• Cooling or heating systems may not work properly.

Resources 

• GLI LC Training Module on Biosafety, slide no. 34.

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