B.1. Explanation of the GRADE appraisal of recommendations
Several factors should be taken into account to appraise the strength of the recommendations, including the available scientific evidence, the balance of benefits versus harms and burdens, differences in values, and the balance of net benefits and costs.
The scientific evidence was assessed through the systematic review designed for the purpose of this guideline (see Annex A for details).
The overall ranking of the strength of the recommendations would consider each of the abovementioned factors as follows.
The higher the quality of evidence, the more likely is a strong recommendation.
The larger the difference between the desirable and undesirable consequences, the more likely is a strong recommendation warranted. The smaller the net benefit and the lower certainty for that benefit, the more likely is a weak recommendation warranted.
The greater the variability in values and preferences, or uncertainty in values and preferences, the more likely is a weak recommendation warranted.
The higher the costs of an intervention, that is, the more resources consumed, the less likely is a strong recommendation warranted.
B.1.1. Strong versus conditional recommendations
The definitions of strong and conditional recommendations are:
strong recommendation — the panel is confident that the desirable effects of adherence to a recommendation outweigh the undesirable effects; and
conditional recommendation — the panel concludes that the desirable effects of adherence to a recommendation probably outweigh the undesirable effects, but is not confident.
B.1.2. Implications of strong and conditional recommendations
The implications of a strong recommendation are:
for patients — most people in your situation would want the recommended course of action and only a small proportion would not; request discussion if the intervention is not offered;
for clinicians — most patients should receive the recommended course of action; and
for policy makers — the recommendation can be adopted as a policy in most situations.
The implications of a conditional recommendation are:
for patients — most people in your situation would want the recommended course of action, but many would not;
for clinicians — you should recognize that different choices will be appropriate for different patients and that you must help each patient to arrive at a management decision consistent with his or her values and preferences; and
for policy makers — policy making will require substantial debate and involvement of many stakeholders.
B.2. Recommendation appraisal tables
Recommendation 1
To help prevent airborne infections, adequate ventilation in a health-care facility, in all patient-care areas, is necessary.
Population: Health-care settings
Intervention: Ventilation
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| Factor | Decision | Explanation |
|---|
| Quality of evidence | Moderate | There is moderate evidence available to suggest that insufficient ventilation is associated with an increased risk of infection (Gustafson et al., 1982; Bloch et al., 1985; Hutton et al., 1990; Calder et al., 1991). |
| Benefits or desired effects | Strong (benefits sometimes outweigh disadvantages) | Reduce the exposure to infectious droplet nuclei by patients and health-care workers.
Improved indoor air quality for patients and health-care workers. |
| Disadvantages or undesired effects | | There is a cost implication to install adequate ventilation in health-care facilities.
Proper operation and maintenance procedures need to be followed. |
| Costs | May be low or high | Low cost is possible if simple natural ventilation is used and properly designed according to local climate.
High initial cost is likely if full mechanical ventilation or high-tech natural ventilation or hybrid (mixed-mode) ventilation is used. |
| Feasibility | Conditional to climate | Mechanical ventilation and hybrid (mixed-mode) ventilation are feasible in all climates, but may be limited due to availability of resources.
High-tech natural ventilation is feasible in most climates and if designed properly, simple natural ventilation is also feasible in resource-limited countries. |
| Overall ranking | STRONG RECOMMENDATION |
| Research gap | There is a need to determine the ventilation rate requirements in health-care settings for infection control. |
Recommendation 2
For natural ventilation, the following minimum hourly averaged ventilation rates should be provided:
160 l/s/patient (hourly average ventilation rate) for airborne precaution rooms (with a minimum of 80 l/s/patient) (note that this only applies to new health-care facilities and major renovations);
60 l/s/patient for general wards and outpatient departments; and
2.5 l/s/m3 for corridors and other transient spaces without a fixed number of patients; however, when patient care is undertaken in corridors during emergency or other situations, the same ventilation rate requirements for airborne precaution rooms or general wards will apply.
The design must take into account fluctuations in ventilation rate.
When natural ventilation alone cannot satisfy the recommended ventilation requirements, alternative ventilation systems such as a hybrid (mixed-mode) natural ventilation system should be used, and then if that is not enough, mechanical ventilation should be used.
Population: Health-care settings
Intervention: Natural ventilation
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| Factor | Decision | Explanation |
|---|
| Quality of evidence | Low | There is no direct evidence available to suggest the direct impact of natural ventilation on disease transmission, though there is strong engineering evidence that natural ventilation can achieve a very high ventilation rate and it is suggested that a high ventilation rate can reduce airborne infection (Menzies et al., 2000). |
| Benefits or desired effects | Moderate (benefits sometimes outweigh disadvantages) | Suitable for mild or moderate climates.
Lower capital, operational and maintenance costs.
Capable of achieving very high ventilation rate.
Large range of control of environment by occupants. |
| Disadvantages or undesired effects | | Easily affected by outdoor climate.
More difficult to predict, analyse and design to ensure airflow direction control.
Reduces comfort level of occupants when hot, humid or cold.
Inability to establish negative pressure in isolation areas, but may be provided by proper design; depends on situation. |
| Costs | May be low and high | Low cost if simple ventilation is used and properly designed with suitable climate.
Can be higher if hybrid (mixed-mode) ventilation or high-tech natural ventilation is used. |
| Feasibility | Conditional to country settings | Natural ventilation is less feasible in extreme climates (extreme cold, hot, noisy, polluted). |
| Overall ranking | CONDITIONAL RECOMMENDATION |
| Research gap | There is a need to determine the natural ventilation requirements in terms of variable ventilation rate and variable airflow direction for infection control in health-care settings. |
Recomendation 3
When designing naturally ventilated health-care facilities, overall airflow should bring the air from the agent sources to areas where there is sufficient dilution, and preferably to the outdoors.
Population: Health-care settings
Intervention: Airflow control in natural ventilation
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| Factor | Decision | Explanation |
|---|
| Quality of evidence | Low | There is moderate evidence available to suggest that incorrect airflow direction is associated with an increased risk of infection (Gustafson et al., 1982; Bloch et al., 1985; Hutton et al., 1990; Calder et al., 1991). |
| Benefits or desired effects | Moderate (benefits sometimes outweigh disadvantages) | Possibly minimized transmission risks between rooms. |
| Disadvantages or undesired effects | More challenging in design and operation of the natural ventilation systems. |
| Costs | May be low and high | Low cost if simple natural ventilation is used and properly designed with suitable climate.
Can be higher if a hybrid (mixed-mode) ventilation system or high-tech natural ventilation is used or additional engineering measures are used to control airflow direction. |
| Feasibility | Conditional to design and control | Natural ventilation is less feasible in providing airflow control and requires careful engineering and architectural design. |
| Overall ranking | CONDITIONAL RECOMMENDATION |
| Research gap | There is a need to study engineering and architectural methods for airflow control in naturally ventilated buildings. |
Recommendation 4
For spaces where aerosol-generating procedures associated with pathogen transmission are conducted, the natural ventilation requirement should, as a minimum, follow . Should the agent be airborne, and should be followed.
Population: Health-care settings
Intervention: Room ventilation for spaces with aerosol-generating procedures
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| Factor | Decision | Explanation |
|---|
| Quality of evidence | Very low | There is indirect evidence available to show that aerosol-generating procedures are associated with an increased risk of infection and ventilation may play a role. |
| Benefits or desired effects | Moderate (benefits sometimes outweigh disadvantages) | Possibly reduced infection risk. |
| Disadvantages or undesired effects | Reduces comfort level of occupants when hot, humid, or cold. |
| Costs | May be low and high | Low cost if simple natural ventilation is used. Can be higher if a hybrid (mixed-mode) ventilation system or high-tech natural ventilation is used. |
| Feasibility | Conditional to country settings | Natural ventilation is less feasible in extreme climates (extreme cold, hot, noisy, polluted). |
| Overall ranking | CONDITIONAL RECOMMENDATION |
| Research gap | There is a need to determine the minimum ventilation requirements for natural ventilation in terms of variable ventilation rate and airflow direction control for aerosol-generating procedures. |
