MRSA vs Hospital Dust

How effective are the current maintenance and cleaning of ventilation and air-conditioning systems in combating MRSA and other HCAI in  British hospitals?

Meticillin resistant Staphylococcus aureus (MRSA) is a prevalent bacterium of UK hospitals, which together with other organisms, remains a cause for concern over increasing incidences of healthcare-associated infection (HCAI). According to Dancer (1999)  MRSA is Gram-positive bacterium which can be transmitted through cross-contamination and direct contact; it thrives at relatively non-humid environment as compared to Listeria and Salmonella and feeds on flakes of dead dry human skin. It can withstand desiccation at a higher temperature 18-37 degrees celsius which makes it resistant to drying and  is thus a frequent component of hospital dust. If we accept that MRSA is a frequent component of hospital dust it is highly probably that it circulates through the air supply and extract via ventilation  and AC systems which poses a major air-borne risk of cross-infection vis-a-vis there is a  greater potential  of  spreading   air-borne MRSA and other  hazardous  HCAI via these  systems  primairly due  re-circulation of hospital dust which potentially include dry sweeping and anti-static mopping as much as polishing buffers.

By the same token there is a plethora of empirical evidence to suggest that increasing air- tightness will lead to health problem which historically  appears to have been significantly substantiated with the emergence of Sick Building Syndrome (SBS) after the 1970's oil crisis.

As hospitals are becoming more airtight and warmer to comply with Building Regulations, this undoubtedly has compromised indoor air qualities significantly.  Both indoor relative humidity (RH) and  air temperature could have wider effects on the colonization and spread of air -borne infection in ducting and supply and extract diffusers.

Clearly, maintaining   RH significantly  below 35% reduces the potential for microbial growth in buildings (Kilcoyne, 2006; Maksion & Swan 2006). Environmental conditions can affect the survival and persistence of microorganisms on surfaces of the indoor environment.  For instance humidity levels are known to influence microbial survival and growth such as mould, mildew and bacteria inside ductwork and ventilations diffusers leading to high concentration of the production of allergens, odour and toxins in the ambient environment. Non-humid and dry environments appear to be optimal for MRSA to thrive given that the comfort zone 21° C to 24° C is well within the MRSA survival temperature range of 18-37° C. What measures can be undertaken to reduce the impact of indoor temperature and relative humidity (RH) on the survival of MRSA and other harmful pathogens given the aforementioned comfort zone temperature and RH requirements?  It becomes increasingly apparent that the risk of cross-infection to patients from ward through the extract and the supply system will be significantly greater than patient to patient transfer and cross-contamination.

Air space per person

Air supply per person

Air changes per hour (ACH)


17 litre/s











Table 1.  Recommended minimum fresh air supply


This might prove to be particularly detrimental to patients in higher risk areas in hospital  such as  isolation rooms, intesive theraphy unit (ITU) Bone Marrow Transplant (BMT) and AE.  Equally, the changes in energy efficiency regulations require buildings to be 'better sealed' and 'more airtight'. The new Part F of Building Regulation have been designed to ventilate buildings having air permeability down to 3m³/h/m² at 50 Pa, allowing designers to plan to ‘worst case' as Buildings Regulations document Part L allows air permeability up to 10 m³/h/m². As hospitals are becoming more air-tight and warmer, they are more likely to require mechanical ventilation and air-conditioning systems but are these  systems  adequately designed for infection control? and  how significant this can  be given that most patients spend up to 90% of their time indoor?

A vicious circle!

Several maintenance and cleaning regimes and protocols have been developed and introduced over the last five years to ameliorate and mitigate the impact of air-borne infection in  heating, ventilation and air-conditioning systems (HVAC) as part of other infection control measures  in British Hospitals. These include, inter alia, deep cleaning, steaming, fumigation, UV, multi- layer filtration and air purifiers amongst many others. Apart from a few anecdotal evidence there is a very limited evidence- based research  to assess the efficacy and robustness of these interventions in reducing air-borne infection in various hospital areas.

How effective and robust are these methods and protocols in controlling the spread of MRSA in  ventilation and AC systems. How effective are the current positioning of supply and extract grilles in promoting effective contaminant dilution and removal of infection agent particularly in high risk areas like isolation rooms and ITU? We know that isolation rooms now locate extract close to the patient at the bed head providing an easy route to spread of infection whereas the majority of all other systems locate supply and extract grilles in the ceiling which is quite paradoxical and essentially contradictory in terms of infection control impacts. Does this promote effective contaminants dilution and removal or does it exacerbate  the situation further vis-à-vis impairing indoor air quality by adversely increasing the circulation of infectious agents in indoor hospital areas? Is there adequate access to maintain and clean ductwork which runs in some hospitals for miles? How robust is air-handling units (AHUs) cleaning? What improvements can be made to maximise MRSA  and other infection control through hospital dust and filtration? What role can facilities managers (FMs) play in implementing and  monitoring  the problem of such increasing  complexity on a daily basis in the light of the wealth of MRSA knowledge-base generated over the past few years?

After years of negligence, hospitals indoor air quality is becoming increasinginly infectious and hazardouss to patients and users alike. What went wrong and how could that possiblyt allowed to happen in both old and flagship British hospitals?

Whilst much emphasis on cleaning of  hard surfaces, floors and walls been given  in varying hospital environments  very limited  and fragmented emphasis has been expended  on  cleaning ventilation and AC systems. Most are   highly oudated  and inaccessible  which significantly hinders operation  and reduce cleaning and  maintemance  protocols effectiveness.  Extract and supply grilles as much as ductwork, air nhanding units, extract fan and discharge are becoming more prone to contamination harbouring deadly bugs. Apart from  significantly higher risk to patients they become increasingly a major medium for air-borne infection.

It is imperative that all ducted systems should be subject to regular yet rigorous  periodic inspection  and intial assessmnent using a dust thickness technique outlined in the HVCA guide TR19 to measure dust accummulation. Both photographic and visual  aids of cleanliness can be used to  support analytical techniques. Certificates of inspection and cleaning must and should be made available for ventilation and air-conditioning systems in the same way legionnella logs are prepared for water systems and asbestos registers for asbestos materials.

Cost-benefit-analysis must preclude any process involved to ensure that the costs of inspection will outweigh significant maintenance and cleaning expenditure on duct cleaning and AHUs replacement on the long-term. What about the cost to patients care and NHS the ultimate beneficiaries of such interventions.

Equally hospitals indoor air quality is  largely accentuated by prescrpitive indoor relative humidity and temperture requirements and air-tightness and air-infilteration thresholds dictated by part F and L of Building Regulations. A radical rethink is most urgently needed to save life.

Dr Ghasson Shabha, MRSA project Co-ordinator, School of Property, Construction and Planning (PCP), Birmingham City University.

0121 331 5184
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