14.4 Environmental controls

The environmental measures aim at reducing the concentration of infectious droplet nuclei in the air.

14.4.1 Ventilation

Ventilation (replacement of inside air with outside air) is the most effective means for reducing the concentration of M. tuberculosis in the air, and as a result, the risk of transmission.

The WHO recommends that in areas where TB transmission might occur, a minimum ventilation rate of 12 air changes per hour (ACH)6 should be achieved. See Appendix 17 for recommendations on ACH measurement.

Effective ventilation can be obtained by natural (assisted or not) or mechanical means.

Natural ventilation
Natural ventilation, especially cross-ventilation (windows/doors in opposite sides of the room), has the best cost-effective ratio. It should be done with the windows and outside doors open (as much as weather conditions permit). Inside doors should be closed so that the flow of air is directed outside and not toward the corridors.

Create shady spaces so that patients, attendants and visitors can stay outside during the day.
Wind-driven roof turbines (whirly birds) or chimneys can also be used to improve natural ventilation, in that they can keep the principle of directing room air towards the exterior. In addition, fans can be used when the natural ventilation flow rate is too low (assisted natural ventilation).

Mechanical ventilation
When natural ventilation cannot reach adequate rates, centralised mechanical ventilation should be considered in some settings, such as within cold climates. Centralised mechanical ventilation relies on the use of mechanical equipment to maintain an air pressure difference between two areas in order to draw air into a room and vent it to the outside. It requires continuous and meticulous maintenance, which renders it costly and difficult to implement and operate.

Advantages and disadvantages of each ventilation technique are presented in Appendix 18.

14.4.2 Architectural considerations

Airborne infection control should be always considered during the planning/construction stages of new health facilities and those being modified. It is important to achieve the following:
– Building layout and design with maximised natural ventilation (assisted or not) and sunlight. Waiting areas should be open on three sides. Design of TB wards should avoid internal hallways with doors from the rooms and wards opening into them. Instead, doors should open to outside hallways that are open to air (this may not be feasible in cold climates).
– Specific areas (open air, sputum collection booth, etc.) should be reserved for procedures with a high risk of M. tuberculosis transmission (e.g. sputum collection, sputum induction, etc.).
– Allow patient flow that reduces exposure of patients at risk to patients that are infectious (e.g. separate waiting rooms for different cohorts, one patient per room in a hospital). If designing a new TB ward, incorporate plenty of single rooms or at least small rooms with 2 to 4 beds for easier separation of the different cohorts of patients. General hospitals should also have isolation rooms available for TB suspects and contagious patients.

Rehabilitation of existing structures in order to maximise natural ventilation could be a viable economical option instead of building expensive systems, like centralised mechanical ventilation.

14.4.3 Ultra-violet germicidal irradiation

Ultra-violet germicidal irradiation (UVGI) lamps1 may be used when adequate ventilation cannot be achieved in high-risk areas. When properly installed, designed, maintained and operated, an UVGI system, in addition to 6-12 ACH ventilation, could be the equivalent of 10-25 ACH7.

For technical information on upper room UVGI, see Appendix 19.
– Main requirements and constraints in UV lamps usage include:
• Expertise in installation and testing;
• Rigorous monitoring and maintenance;
• Electricity, relative humidity less than 70%, good air mixing.
– Potential hazards include: Transient eye and skin injuries from overexposure, mercury poisoning (broken or mishandled lamp).

14.4.4 Areas requiring specific measures

Sputum collection areas
These areas must be settled, wherever possible, outside in open air where bacilli will naturally be dispersed by wind rather than in a closed room where the concentration of bacilli will be high.
In cold regions, sputum collection should be performed in very well ventilated indoor rooms (at least 20 ACH) or in well ventilated rooms (at least 12 ACH) equipped with a UVGI system.
Another option for sputum collection areas in cold climate regions is to assign a specific room of small size (1 m2) with one single glass door opening outside. Keep the door largely open for 5 minutes between each patient. The small volume of air in this room facilitates rapid ventilation.

All laboratories should undergo a risk assessment, and IC measures should be adapted accordingly. In any case, limit the access to all TB laboratories.
The use of ventilated workstation (Appendix 7) is strongly recommended for smear preparation (microscopy and test Xpert). In laboratories where culture are carried out, biological safety cabinets type II must be used.
Laboratories must have easy to clean working surfaces (avoid wood) to allow proper disinfection. They should also have large windows to let in sunlight and allow natural ventilation if the laboratory has no mechanical ventilation.
Water-filters should be used to avoid contamination by saprophyte mycobacteria that are sometimes present in the water.

Ref Notes

UVGI inactivate bacilli. Natural light dries the droplet but does not inactivate bacilli.