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INF ECTION P R EVENTION


rates of nosocomial transmission. Yet, as research is showing,6


there have been high


levels of nosocomial infections rates in UK hospitals for SARS-COV-2 – as high as 25% in some areas.7


Of course, these high rates of nosocomial infection are not just limited to SARS-COV-2. In his groundbreaking paper ‘The Airborne Transmission of Infection in Hospital buildings: Fact or Fiction?’ Beggs began questioning some of the conventional views around aerosol transmission.8


This of course


included Tuberculosis but also aspergillus, pseudomonas, acinetobacter and MRSA. In his conclusion he notes, ‘Many micro- organisms remain viable in the aerosolised state even though they are non-culturable, with the result that true air bio-burden counts are usually underestimated.’9 Other research has gone on to show that respiratory droplets are mostly ‘less than 100µm in diameter and these evaporate rapidly in the surrounding environment and become droplet nuclei, which suspend in the air or are transported by airflow.’10 This of course ties in with Wells’ original research from 1934. It is aerosols that present the prime transmission danger within the built environment and sadly a huge number of current ventilation systems are not installed to a sufficient standard or in a way that enables sufficient protection. Let us look at filter grades and types. European regulations for general filtration changed from EN779 to ISO16890 in 2018 (See Table 1).


The majority of existing healthcare rooms with ventilation have filtration at either G4 or F9.11


This means that for a single air pass, the efficiency that can be expected for stopping a virus is either near non-existent (G4) or around 40%. This is without taking into account documented issues such as ‘entrainment’ where air can flow against the current (i.e. in the wrong direction). Simply changing the filter grade isn’t feasible in most areas because a higher-grade filter is denser and therefore requires greater pressure to force air through it.


Most systems have been built to be ‘fit for purpose’ and therefore cannot cope with even slight changes to filter density – something which can be attested to by


EN779 Grade General


G1 to G4 Medium


M5 to M6 Fine F7 to F9


ISO16890 Grade Efficiency


ISO Coarse ISO ePM10


Supplemental air cleaning should be seriously considered for all ward areas. With the increased awareness of aerosol generating procedures, such as CPAP, endoscopy and dentistry, this obviously applies for SARS- COV-2. It should also apply for all other pathogens such as influenza A, measles, C.diff and aspergillus.


many staff who have complained that their air conditioning isn’t working during recent hot summers. To really deal with room bio- loading, due to aerosols, we need to look at supplementary systems and, in some cases, also pressure differential. The traditional ‘HEPA’ filter has been based on a standard known as EN1822, which is now being superseded by ISO29463. HEPA stands for ‘High Efficiency Particulate Air’. This isn’t one grade but a range of grades which then leads to a higher grade known as ULPA. All of the material for these filters (not the filters themselves)


ePM1 (1µm) ePM2.5 (2.5µm) ePM10 (10µm) Efficiency


/


Efficiency /


5%-35% to 10%-45% to 10% -40% 20%-50%


ISO ePM2.5, ePM1. 40% to 90% 65%-95% Table 1: Basic European Filter Grades 72 l WWW.CLINICALSERVICESJOURNAL.COM


Efficiency /


40%-70% to 60%-80%


80%-100%


is tested at 0.3µm. However, there is no assurance with either of these grades that the filter is working correctly. It is for this reason WHO specifically advocates testing all systems independently,12


something we


do for all of our own systems using a higher standard (EN14644 part 3).


When it comes to airborne disease, we know that the best option is to have very low levels of the pathogen circulating; the lower the better. Thus, to offer an assurance that no airborne pathogen is passing through a filter system to contaminate the air environment, the minimum level is H14 or ISO45H. Despite this, the only areas recommended for H14 filters under HTM 03-01 are pharmacy aseptic suites and category 3 or 4 containment rooms.13 Supplemental air cleaning should be seriously considered for all ward areas. With the increased awareness of aerosol generating procedures, such as CPAP, endoscopy and dentistry, this obviously applies for SARS-COV-2. It should also apply for all other pathogens such as influenza A, measles, C.diff and aspergillus. It is interesting that the food and


JANUARY 2021


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