STLS: Airborne Infection Control

Mycobacterium tuberculosis is transmitted in airborne particles called droplet nuclei that are expelled when a person with pulmonary TB coughs, sneezes, shouts, or sings. People nearby may breathe in these bacteria and become infected. 

Airborne infection control is essential to prevent the spread of TB within a health facility and other settings.

Hierarchy of Controls to Reduce Risk of Transmission of TB (see the Figure)

Figure: Hierarchy of controls to reduce risk of transmission of TB

Environmental factors that influence transmission of M. tuberculosis are elaborated in the table below.

Resources

1. Guidelines on Airborne Infection Control in Healthcare and Other Settings.
2. Tuberculosis Infection Control.

Ventilation is defined as the supply/ distribution/ exchange or removal of air from spaces by mechanical or natural means.

Airflow is a natural process whenever there is change in temperature or pressure. Air keeps moving displacing the room air, and the time to replace the entire in-room air depends on the size of the room, the openings, and the presence of additional/mechanical force. This air-flow, also called ventilation, will allow the entry of outside air or clean recirculated air to remove extra heat, humidity and infectious aerosols from occupied spaces to meet health and comfort requirements. 

When fresh air enters a room, it dilutes the concentration of particles in room air including aerosols responsible for the transmission of TB that can otherwise remain suspended in the air for significant periods of time.

Thus, ventilation is recognized as an important factor influencing the transmission of airborne diseases.

Types of Ventilation at Designated Microscopy Centres (DMCs)

1. Natural Ventilation (Figure below)

• Natural ventilation at DMCs is achieved by designing a laboratory layout that supports the unrestricted flow of natural air.
• Doors and windows should be kept open to bring in fresh air from outside.
• Opening windows and doors on opposite walls will also allow for cross ventilation.
• The placement of furniture, equipment, supplies etc. at DMCs should not block or restrict the opening of doors and windows.

Figure: Natural ventilation achieved by opening doors and windows or using mechanical ventilation using fans and an exhaust fan for air mixing and directional flow (A); the flow of natural air should not be restricted by blocking doors and windows (B); Cross ventilation is not adequate if there is only one entry point for outside air (C); Source: Tuberculosis and HIV Co-Management and Tuberculosis And Airborne Infection Control.

2. Mechanical Ventilation: When the movement of air is driven by a mechanical device, it is called mechanical ventilation.

• DMCs are equipped with fans and exhaust fans as the simplest means of mechanical ventilation for air circulation and directional flow of air. Exhaust fans fitted in windows/ ventilators exchange air from inside the laboratory to the outdoors.
• Ceiling fans/ tabletop fans/ pedestal fans have rotating blades to circulate air inside the room. Tabletop and pedestal fans can be positioned in the room to allow the directional flow of air.

3. Hybrid/ Mixed-mode Ventilation

• In hybrid/ mixed-mode ventilation exhaust and/or fans are used in DMCs in combination with natural ventilation to obtain adequate air dilution when sufficient airflow cannot be achieved by natural ventilation alone.

The table below compares the advantages and disadvantages of the different modes of ventilation.

Table: Summary of Advantages and Disadvantages of Different Types of Ventilation; Source: Guidelines on Airborne Infection Control in Healthcare and Other Settings.

Resources

• Guidelines on Airborne Infection Control in Healthcare and Other Settings.
• Tuberculosis Infection Control, CDC.
• Tuberculosis and HIV Co-Management.
• Tuberculosis and Airborne Infection Control.

The administrative measures at a health care facility play an important role in preventing the spread of TB in health care settings. It includes Administrative controls for outpatient and inpatient settings

Administrative measures at Outpatient(OPD) settings
1. Screen for respiratory symptoms as early as possible upon patient’s arrival at the health care facility thereby reducing the overall stay of such patients in the healthcare facility

• screening at registration counter itself by asking simple questions related to chronic respiratory symptoms, and those suspected to have TB can be prioritized for further management
• screening when patients are in waiting area- by volunteers/health staff

2. Provide patient education and counseling on cough hygiene and sputum disposal

• paramedical staff or volunteers should educate and reinforce cough etiquette while the patient is in the waiting area
• educate patients on availability of bins with disinfectants for disposal of sputum
• display of posters on cough hygiene and sputum disposal in the waiting areas

3. Segregate patients with respiratory symptoms

• having separate waiting area for chest symptomatics within the overall outpatient area
• implement a patient flow control mechanism so that screened chest symptomatics are diverted to special area rather than the common waiting area
• well ventilated waiting areas to reduce overall risk of airborne transmission

4. Fast-track patients with respiratory symptoms

• fast-track patients for clinical and laboratory evaluation
• fast track chest radiography and sputum examination with priority slips/referrals

Administrative measures at Inpatient (IPD) setting
1. Minimize hospitalization of TB patients

• whenever possible, manage patients entirely as outpatients thereby avoiding hospitalization and the risk of exposing other patients and staff

2. Establish separate rooms, wards, or areas within wards for TB patients

• patients with TB should be physically separated in different rooms/wards from other patients so that others are not exposed to the infectious droplet nuclei
• separation of TB patients from vulnerable and immune-compromised patients is essential

3. Educate and counsel inpatients on cough hygiene and provide adequate sputum disposal

• educate and display posters on cough hygiene and safe disposal of sputum in bins with disinfectants
• provide masks to all admitted patients and educate on proper use of masks

4. Establish safe radiology procedures for TB patients

• schedule inpatient chest radiography for non-busy times
• provide priority service to minimize the length of time spent in the department

Resources

1. Guidelines on Airborne Infection Control in Healthcare and Other Settings.
2. Tuberculosis Infection Control.