environmental controls

5.1 General considerations

Environmental controls are the second line of defence for the prevention of nosocomial transmis- sion of MDR-TB. When employed in conjunction with administrative controls, environmental controls can be effectively used to reduce the concentration of infectious particles to which HCWs or patients are exposed. Environmental controls are therefore most important in areas where there may be exposure to highly concentrated infectious particles, such as wards containing large numbers of infectious MDR-TB patients, sputum induction areas, bronchoscopy suites, laboratories performing culture and susceptibility testing, and autopsy rooms.

A variety of environmental controls can be used to reduce the number of aerosolised infectious particles in the work environment. Although some environmental controls do not require a large ex- penditure of resources, most are expensive and technically complex. Implementation of these control measures should be guided by the assessment of risk as well as available resources.

The administrative control measure of physically separating suspected or known infectious MDR-TB patients from others is an essential first step prior to the implementation of environmen- tal control measures. This can be achieved by placing infectious patients in a separate room, ward, or

building. Most environmental control measures are easier to implement and maintain if their use can be limited to part, rather than all, of a large facility.

International guidelines should be used when drawing up institutional infection control plans

World Health Organization

Appropriate signage is an administrative measure used to identify high risk areas

The best way of reducing high concentrations of infectious particles in the work environment is through ventilation, ie. the movement of air to ensure dilution and air exchange. Ventilation may be achieved as follows:

• Using air currents generated from outdoor winds; • By convection using indoor sources of heat;

• By mechanical fans that pull air in a directional manner; • By various types of mechanical ventilation.

Ideally, fresh air is constantly pulled through a room and safely exhausted to the outside, such that the air is changed several times every hour (Figure 14.1.).

Isolation rooms for infectious MDR-TB patients is highly desirable, but not feasible in most resource-poor settings

Centres for Disease Control and Prevention

Direcction of airflow under the door: Positive pressure Airflow Airflow

Bed Bed Bed Bed Bed

Air

Conditioner

Module 14 Infection control • Page 173 Where the establishment of adequate ventilation is not feasible for climatic or other reasons, alterna- tive means of reducing the concentration of infectious particles include the use of ultraviolet germicidal irradiation (UVGI) to kill infectious organisms or air filtration methods to remove infectious particles. However, these latter methods are of limited effectiveness unless combined with methods to mix and move the air.

Environmental control measures may include:

• Open windows that maximise natural ventilation and dilute the air (the simplest and least

expensive technique).

• Overhead fans, which are already present in many settings, and may be used to further enhance

natural ventilation in settings where windows can remain open.

• Exhaust fans that provide directional air flow in areas where open windows and overhead fans

are not sufficient. Directional air flow refers to the introduction of a ‘clean’ air stream into the space occupied by the infectious patient to dilute the concentration of airborne tubercle bacilli and thereby reduce the risk of transmission. These fans, which are usually placed in windows, are designed to move air containing infectious particles to the outside and replace it with air coming from “clean” parts of the facility or from the outside.

• Exhaust ventilation systems that provide at least six air changes per hour and prevent contami-

nated air from escaping into ‘clean’ parts of the facility may be considered where risk is deemed extremely high and the financial means exist. The most common way in which such ventilation can be established is through the use of negative pressure ventilation, in which a room is kept at negative pressure relative to the surrounding area and air is drawn into the room from the corridor and exhausted directly outside.

• Adjunctive measures such as the use of high efficiency particulate air (HEPA) filters or ultravio- let germicidal irradiation (UVGI) may be helpful but should not be relied upon as substitutes for the environmental controls mentioned above. Their usefulness is limited unless air move- ment is adequate to ensure contact of infectious particles with these devices, and it is difficult to assess their effectiveness in field use.

• HEPA filters should be replaced only by properly trained staff. A very high risk exists if un- trained staff try to change HEPA filters

5.2 Natural ventilation

Natural ventilation was the only form of environmental infection control for TB until relatively recently.

Natural ventilation can be used in medical wards or other sites in health facilities in temperate or tropical climates where windows can be left open. Natural ventilation can occur when a room or ward is of open construction with free low of ambient air through open windows (in one side and out the other). Maximizing natural ventilation patterns for the hospital, clinic, ward or room may be the simplest and least costly approach to achieving better ventilation. Various strategies may be employed:

• Waiting areas, examination rooms, and wards should be ‘opened’ to the environment (eg. es- tablished in covered open areas or in areas with open windows). Additionally, windows may be installed that would allow for more ventilation. Windows should be placed to the open environ- ment and not to other wards.

• Ceiling fans may be used to facilitate air mixing and movement. Since diluting and exchanging rather than just mixing the air is the objective, ceiling fans should be used in conjunction with open windows.

• Because of the increased risk of creating more highly concentrated infectious aerosols during coughing, sputum collection should be done in a well-ventilated area, preferably outdoors and well away from other persons. Care should be taken to assess these areas to assure that there is good air movement since some areas immediately adjacent to buildings or on porches or veran- das may have poor air movement.

In many situations, it is not possible to establish cross-ventilation. Closed rooms that contain air with aerosolised infectious particles present a particular risk. A room with an open window at one end provides air exchange near the window; however, little air is exchanged a short distance from the window. In such settings, having another window in the room open or keeping a door open may improve air exchange, but having open windows and doors does not guarantee good dilution ventilation.

A common problem in settings that rely on natural ventilation is that patients or staff close the win- dows during cooler weather or at night. There is likely to be variability of air flow patterns due to varying weather patterns or to the presence of other structures blocking air currents. Where natural ventilation is used, air movement can be easily assessed using smoke tubes or similar measures. If inadequate addition- al mechanical or other measures may be needed, especially in areas where risk of transmission is high.

Managua. “Ventilation and sunshine are very important in the house.”

Module 14 Infection control • Page 175 5.2.1 Mechanical ventilation

Mechanical ventilation should be used in situations where natural ventilation does not produce

adequate airflow to reduce the concentration of infectious droplet nuclei. Mechanical ventilation is es-

pecially recommended in areas in which there may be high concentrations of infectious aerosols, such as: • Wards or rooms containing large numbers of infectious MDR-TB patients;

• Bronchoscopy suites; • Sputum induction areas;

• Laboratories handling concentrated sputum specimens and cultures; • Autopsy or mortuary rooms.

If mechanical ventilation is used, it is important to use equipment with sufficient power to facilitate air entry into, and exhaust from, the room or area. In other words, if no air is allowed to enter the area, then it will be impossible to exhaust air. It is also important to attempt to direct air movement so that infectious particles produced by coughing patients are exhausted away from others.

Directional air flow from a ‘clean’ area, across the HCW, across the patient, and to the outside should be maintained. The area where air is entering should be located away from the air intake to avoid ‘short-circuiting’ whereby newly exhausted contaminated air is drawn back into the room through the air intake. It should be noted, however, that if patients are highly mobile, the potential benefit of directional airflow will not be realised.

The simplest form of mechanical ventilation is exhaust fans, which are generally placed in windows and move air from inside a room to the outdoors. If exhaust fans are used, it is important to ensure that airflow is adequate, and also that air flows across the room (not in and out the same window or vent). This can be monitored through the use of smoke tubes or other devices designed to assess direction of airflow.

Window fans that move air from inside the room to the outdoors are the least expensive and most

feasible method of providing mechanical ventilation. In most circumstances, they can serve to effectively dilute air containing infectious particles. They may also be more acceptable to staff and patients than keeping windows consistently open, although they too may decrease the temperature of the room.

Mechanical ventilation is not without its limitations:

• Ventilation rates in rooms may vary depending on whether doors or windows are open or closed as well as the situation in other rooms on the same ventilation system.

• Systems may not function properly as a result of poor maintenance, electrical power failures, or poorly planned renovations.

• Poorly designed or maintained mechanical ventilation systems may provide false reassurance to health care workers. In addition, they can also be a source of indoor air quality problems that may affect the health of HCWs and patients.

5.2.2 Monitoring of ventilation and ventilation systems

Ventilation systems should be evaluated regularly to determine that they are func- tioning properly. The simplest evaluation includes the use of visible smoke (eg. using ‘smoke tubes’) to monitor proper airflow di- rection. More sophisticated tests utilising a flow velometer or tracer gas analyses also can be used to determine airflow rates and calcu- late the number of air exchanges per hour. Evaluations should be conducted periodically and documented in a maintenance record.

Many countries have their own ventila- tion standards, which should consider those published by ASHRAE, the American Society of Heating Refrigeration and Air Condition- ing Engineers (http://www.ashrae.org/)

5.2.3 Ultraviolet germicidal irradiation (UVGI)

Laboratory studies show that M. tuberculosis is killed if the organisms are exposed to UVGI suf- ficiently. For this reason, UVGI has been recommended by some as an inexpensive environmental control measure. For it to be effective, however, contaminated air must come in contact with the light rays, which may be a major problem in areas where air circulation is poor, and its effectiveness may be limited in areas where the humidity is high or in dusty areas. Furthermore, skin and eye reactions may occur in HCWs and patients from overexposure if the UVGI is not installed and maintained prop- erly. A final major limitation to the use of UVGI is the inability to assess its effectiveness in the field, especially given the various types of available products, positions in rooms, and variability of room air mixing in various settings.

If UVGI is installed a regular program of maintenance is essential. Responsibility should be as- signed to ensure that the lamps are dusted periodically and changed at regular intervals. It is also impor- tant to periodically assess airflow to ensure that air flow patterns maximise M. tuberculosis UVGI killing. The quality of UVGI lamps is very important. Usually a good one will last 5 000 to 10 000 hours (7 - 14 months). After that, the irradiance drops off rapidly. Ideally, irradiance should be measured with a ra- diometer. In addition, care must be taken to minimize risk to HCWs and patients who, if inadequately protected, may complain of skin and eye irritation. Maximum permissible exposure times for selected effective irradiance levels are available (refer to the Centers for Disease Control and Prevention website for more information: htttp://www.cdc.gov/).

Upper room UVGI is intended to be used while rooms are occupied, not to sterilize empty rooms, as is commonly done in some parts of the world. It is much more important to decontaminate air while the infectious source and other occupants are present, and upper room UVGI is designed to do that without significant radiation risks.

A growing number of manufacturers of fixtures designed for upper room use now exist in low- income countries and can provide products at lower cost. However, there are currently no standards and the buyer still needs to obtain advice from someone knowledgeable on the subject.

In addition to UVGI designed for upper room use, germicidal UV is sometimes used in ventilation ducts or in fan-driven air sterilizing devices mounted on ceilings or walls, or portable units that can be moved from room to room. Their efficacy is limited by the number of air changes they can produce, especially in large spaces.

Ventilation measurements performed by a team of environmental specialist

Module 14 Infection control • Page 177 Laboratories that process specimens that may be MDR-TB especially need strict environmental controls. These aspects are addressed in other documents.