The enemy within

In spite of concerted efforts to maintain a clean clinical environment, hospital acquired infections (HAI) remain a key concern in connection with any hospital stay. A significant number of patients contract HAIs and tragically a percentage of these cases are fatal. Aside from the fundamental detrimental effect on patient wellbeing, the average HAI hospital cost per patient is estimated to be in excess of £30,000. Strategies from hand washing to more transparent reporting have helped to reduce this threat but not eradicate it, and indeed it may get worse: A recent Lancet special editorial warns of superbugs in the looming 'post antibiotic' age. 

 

Battling cooling coil biofilm

When we bring ambient air into our buildings and cool it by passing it over a cooling coil, the dew point drops and moisture from the air is deposited on the coil matrix creating the perfect environment for mould to grow. Add to this the particles that get past our primary filters, and soon we have an established biofilm colony. Some of the most common microorganisms found growing in the biofilm include MRSA, Pseudomonas, Penicillin and Aspergillus.

 

Coils are seldom cleaned more than once a year yet the mould colony can double in size every four hours. This allows the biofilm virtually unhindered opportunity to grow. Although many hospital systems may use 100% fresh air, after passing through the coil, the fresh air becomes contaminated where it collects microorganisms growing in the biofilm of the coil and drain pan before effectively and rapidly dispersing them throughout the building’s air system.

Some might argue that HEPA filters provide protection. HEPA filters are rated to 99.997% efficiency. In a cubic foot of air you can have 100,000 micro particles; therefore with air in the duct travelling at 800ft per minute, you can have 8,000,000 particles. If only 0.003% break through the HEPA filter you can have 24,000 micro particles per minute.

Microorganisms affect both patient and health workers and contribute to the high staff absenteeism found in healthcare organisations. Clinical trials conducted in Britain, Europe and the US confirm that 80-90% of bacterial contaminants found in post surgery wounds come from colony forming units (cfu) which are present in the air of operating theatres. 

The US GSA (General Services Administration), the Centre for Disease Control (CDC), ASHREA (the American Society of Heating, Refrigeration and Air Conditioning Engineers) the Hong Kong Government and the Royal Navy recommend the use of UVC. ASHRAE and ISO are developing standards for the use of UVC in air-conditioning. Our Department of Health in their Health Technical Memorandum 03-01 advise: "cooling coils will need to be periodically cleaned or decontaminated”. We would suggest that you need to clean the coils daily and that continuous cleaning would be preferable. So how do we treat the issues of biofilm growth within the coil?

 

Using UVC light

A popular approach to cleaning is to manually treat the coil through high pressure (HP) cleaning, vacuuming and biocide treatment. With HP cleaning, poor accessibility means that effective cleaning requires complete coil removal. A modern coil design has up to 14 plates per inch of coil, with very little space between the plates. HP cleaning is unable to penetrate the coil to its core and typically compacts the biofilm even further into the coil where it continues to flourish and begins regeneration.  

The use of a vacuum to clean coils only removes the biofilm from the coil’s outer surface. Even when using biocides it is difficult to penetrate the coil to the core. There is also the risk of potential harm if the chemical bi-products get into the building airstream where it can affect the health of occupants.

We recommend the irradiation of the coil with high powered germicidal UVC (C Band) light. This treatment offers continuous cleaning of the system including effective cleaning of the whole coil (to the full depth of the matrix) and treatment of the condensate and drain pans. We have application specific case studies and 18 years of experience proving that high output UVC is extremely effective at stopping the dissemination of viruses, bacteria and mould throughout air conditioning systems.

 

We have also proven that we can reduce downstream biofilm fouling of the ductwork as the coil is the main food source for this fouling. We can extend the life of HEPA filters through the same process. One warning:  Not all UVC systems are equal and most do not work well in the cold air of air-conditioning. Insist on high output verified by independent tests such as the US EPA.