In June 2007, the World Health Organization (WHO) released new guidelines entitled Infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care — WHO interim guidelines (WHO, 2007). In this guideline, natural ventilation was considered among the effective environmental measures to reduce the risk of spread of infections in health-care settings.
The purpose of this latest guideline is twofold:
to promote natural ventilation design for infection control in health care (
Part 1); and
to describe the basic principles of how to design, construct, operate and maintain an effective natural ventilation system for infection control (
Part 2).
This guideline is primarily developed for engineers and architects who design or operate health-care facilities. The guideline is also useful for health-care workers, particularly infection-control professionals who work in health-care facilities. The guideline recognizes that the hospital designers, operators and health-care workers need to work together for effective infection control.
This guideline applies to diseases that can be transmitted through fine droplets or through droplet nuclei. The guideline describes how an airborne precaution room and its adjacent areas can be designed to provide natural ventilation control of infections. However, this guideline does not include thorough descriptions for other infection-prevention and control measures.
The development of this guideline involved:
a two-day multidisciplinary consensus meeting on the scope and main elements on use of natural ventilation for infection control (May 2007);
a systematic review of the literature covering the association between ventilation and infection, and natural ventilation solutions (March-December 2008) (see
Annex A for details);
WHO external panel review and outline of the main recommendations (November-December 2008); and
WHO internal and external peer review (January-May 2009).
The main recommendations are listed in the following box.
Main recommendations
To help prevent airborne infections, adequate ventilation in health-care facilities in all patient-care areas is necessary.
Overall ranking: Strong 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 hybrid (mixed-mode) natural ventilation should be considered, and then if that is not enough, mechanical ventilation should be used.
Overall ranking: Conditional recommendation
- 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.
Overall ranking: Conditional recommendation
- 4.
For spaces where aerosol-generating procedures associated with pathogen transmission are conducted, the natural ventilation requirement should, as a minimum, follow Recommendation 2. Should the agent be airborne, Recommendations 2 and 3 should be followed.
Overall ranking: Conditional recommendation
These four recommendations were developed by the systematic review external panel using the GRADE appraisal system during the panel's meeting in Geneva in November 2008 (see Annex B). In areas where vector-borne disease is endemic (e.g. malaria, dengue), the use of natural ventilation should not affect in any way the usage policy or practice of mosquito nets.
Only basic principles of design, construction, operation and maintenance are described in this guideline, and the designers will need to consult engineering design guides and textbooks for technical details of natural ventilation. The readers are reminded about the limitations of natural ventilation when there is a lack of natural forces, such as winds and breezes, especially for the delivery of the high airflow rates recommended in this guideline for airborne precaution rooms. Users are reminded not to rely solely on this guideline for design guidance for their naturally ventilated facilities.
Naturally ventilated hospitals or airborne precaution rooms need to be designed properly for natural ventilation to provide the recommended ventilation rates, otherwise, factors such as the lack of directional control of airflow may lead to a potential for transmission of infection. Interested readers should obtain or consult the referenced technical documents when contemplating renovation or construction using natural ventilation.
This guideline will be reviewed five years after its publication to include new data on the association between natural ventilation rates and infection.
Implementation plan
The guideline is a new area so there is no adaptation plan available.
A follow-up project has already started and covers “low-cost health-facility design with naturally ventilated infection-control characteristics”. It aims at providing design assistance for naturally ventilated, low-cost health facilities in low-income settings. More information regarding this may be found at http://www.who.int/csr/natvent.
WHO intends to provide sample designs, plans and guidance for the renovation and construction of health facilities to be posted on a web page for free downloading. This will build on the current guideline to encourage and facilitate the provision of low-cost healthcare facilities with infection-control characteristics, in low-income countries, that use affordable and sustainable means and (if feasible) natural ventilation.
