PRoBE is a new research initiative to provide the knowledge to address the growing issues of pathogen spread in building systems.
PRoBE was established at Heriot-Watt University with the aim of characterising and defining the aerosolisation, transmission, and infection risk posed by building systems, particularly the building drainage system.
PRoBE is a cross-disciplinary research group of engineers, mathematical modellers and microbiologists at Heriot-Watt University. The acronym stands for Pathogen Research in the Built Environment (PRoBE). The PRoBE logo and more information can be found at the research group website (www.pathogenresearch.org.uk).
It is intended that this cross-disciplinary group will look at a range of different issues relating to infection spread in buildings. Having been established just over a year ago, the group has already had success in highlighting the complex issues in this area and brings a fresh approach to the discipline.
The Group is led by Dr. Michael Gormley and supported by Dr. Tom Aspray who is a microbiologist, and Dr. David Kelly who has worked on building drainage systems for over 10 years.
Bioaerosols can pose a significant risk to the spread of infection and disease within buildings. Research activities focus on the characterisation of bioaerosol generation and transmission, coupled closely with the development and application of advanced numerical models for the prediction of bioaerosol transport.
A significant area of research focuses on the transport of bioaerosols within the sanitary plumbing and sewerage system and their cross-transmission into the building. Laboratory tests, using Pseudomonas putida KT2440 as the pathogenic agent within a toilet flush, found that the generated bioaerosols could be spread from one floor of a building to another via the building drainage system. If a defect within the system exists such as, for example, the loss of the seal within a water trap, then the bioaerosols could enter a room on an upper floor and contaminate every surface within that room. Such a cross-transmission route depends on the following confirmed conditions:
- The sanitary plumbing and sewerage system is a reservoir of pathogenic organisms.
- Bioaerosols are generated during appliance flush.
- Airflows within the sanitary plumbing and sewerage system move both in the upward and downward directions and circulate between floors.
- Bioaerosols can be transported on the airflows that exist within the sanitary plumbing and sewerage system.
- A defect, such as an empty U-bend, allows air to move from the system into the building.
Viral Transmission in Tall Buildings
As a common feature of most global cities, tall buildings offer a number of advantages, whether it be to provide offices or homes when urban space is not available or to make an iconic statement on the world stage. However, these “cities in the sky” can also facilitate the rapid spread of infection from one person to another due to the high density of people in a single building. Using advanced numerical modelling techniques, researchers at PRoBE were able to confirm the World Health Organisation conjecture that a high cluster of cases of SARS, reported at the Amoy Gardens residences in Hong Kong in 2003, was caused by the vertical transmission of the virus between apartments via both the sanitary plumbing system and the service risers. The 321 confirmed cases of SARS and 42 fatalities suffered by the residents highlight the risk of infection spread within buildings, especially the significance of a vertical transmission route which is particularly unique to tall buildings.
By modelling air flow movement and air pressure wave propagation within the sanitary plumbing system, the PRoBE research was able to demonstrate the likely circumstances within the building that resulted in the rapid spread of the virus. The index patient (the first resident to become infected with the virus) lived on the 16th floor of the 36 storey building. Infected faecal particles were discharged into the building drainage system during the diarrhoeal phase of the infection. The flushing of the WC caused the generation of airborne bioaerosols within the system’s vertical stack. A number of dry floor drains, together with some appliances with no fitted water trap seals, provided a route for the ingress of virus-laden bioaerosols from the building drainage system and into the bathroom, driven by the transient pressures prevailing within the system, natural buoyancy, and the negative pressure created by the bathroom extract fan. After passing through the extract fan, the bioaerosols were then exhausted into the external service riser which acted as a channel to spread the virus to upper and lower apartments via open windows. This mechanism of viral spread was attributed to the infection of residents in some 11 apartments below the index patient and 27 apartments above the index patient – firmly highlighting the significant risk of vertical transmission of infection in tall buildings.
Infection Spread in Hospitals
With up to 9% of all patients in the UK contracting a Healthcare Acquired Infection and an associated annual cost to tax payers estimated at £1 billion, the control and reduction of the spread of infection in hospitals is a top priority for the NHS in the UK. Researchers at PRoBE have identified the building drainage system as a potentially significant, yet often forgotten, source of infection spread within hospital buildings.
The building drainage system is one of only a few engineered systems that interconnect all parts of a building, and it is the only one that acts a collection network for human waste. In a hospital building, this waste has a high potential for pathogenic contamination, making the building drainage system a potentially rich reservoir for pathogenic microorganisms. Failures within the system, such as empty water trap seals at appliances or wastewater backup due to blockages, can contribute to the spread of pathogens from the building drainage system into the hospital building – considerably adding to the risk of infection spread.
Research carried out by PRoBE in hospital buildings using polymerase chain reaction (PCR) tests on waste water samples confirmed that the sanitary plumbing and sewerage system is contaminated by pathogens released directly to the system by infected patients. In one example, the building drainage system tested positive for Norovirus GII over a number of weeks during an outbreak within the hospital building.
Furthermore, measurement of the conditions within the hospital sanitary plumbing and sewerage system showed average temperatures of just over 24°C and an average humidity of almost 97%. The warm and humid conditions that exist within the system not only aides pathogen survival, it also facilitates the airborne transmission of aerosolised pathogens around the system, and potentially into the hospital building, through air movement and buoyancy effects.
At the heart of the work carried out by the PRoBE group is an adherence to excellence in data collection and a rigorous approach to both engineering modelling and microbiological analysis. Molecular techniques such as PCR are used to generate mathematical equations suitable for inclusion in a 1-D method of characteristics model, AIRNET, which is currently being updated to include an algorithm for the simulation of microbial transport on building drainage airstreams.
The work of the PRoBE group is gaining momentum and has contributed to providing solutions to difficult infection spread problems so far. We are hopeful and confident that the group can go on to add to the knowledge base we have started with the aim of providing improved public health for all buildings in the future.
Dr. Michael Gormley, November 2015