key: cord-0863435-di1s6vy7
authors: Fennelly, Μehael; O’Connor, David; Hellebust, Stig; Murphy, Noel; Casey, Colman; Eustace, Joseph; Plant, Barry J.; Sodeau, John; Prentice, Michael B.
title: Effectiveness of a plasma treatment device on microbial air quality in a hospital ward monitored by culture
date: 2020-11-12
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2020.11.006
sha: 1ce810f5e16e03fd87ed517e6b8d902888d8ef2d
doc_id: 863435
cord_uid: di1s6vy7

We analysed the effectiveness of plasma treatment on airborne bacteria and surface counts on a 14-day intervention with plasma air treatment within a 4-bedded bay in an adult respiratory ward at Cork University Hospital. 100L air samples were collected twice daily every weekday for 4 weeks, with settle plates and surface swabs. The plasma treatment did not produce an effect on airborne bacteria and fungi which was detectable by culture. We cannot exclude that culture-based sampling may be insufficiently sensitive to detect an effect, or that the duration of the study was insufficient for plasma treatment to affect a complex environment.

The World Health Organisation (WHO) reports that 7.6 per 100 patients in high income countries acquire a healthcare associated infection (HAI) [1] . Although there are many routes to infection spread, airborne transport may be responsible for up to ten per cent of all HAIs [2] . The current COVID-19 pandemic has highlighted the need for effective and efficient removal of airborne pathogens from the air by ventilation, including in the healthcare environment [3] . Airborne microorganism culture is applied to parts of the hospital environment where patient contamination by airborne organisms is recognised to be particularly harmful, such as operating theatres. However, although air culture data has been reported for other areas only empirical airborne microorganism standards for operating theatres exist [4] .

Filtration, removal of particulates from air, is the usual method of improving indoor air quality in modern buildings. An existing heating, ventilating, and air-conditioning (HVAC) system may be augmented by a "portable air cleaner". The US Centers for Disease Control and Prevention (CDC) recognises portable HEPA (High Efficiency Particle Air) filtration devices as a means of increasing the effective number of air changes per hour (ACH) in controlled environments [5] .

The current study relates to an adult respiratory ward at Cork University Hospital. The ward is ventilated by a heat recovery ventilation system with a HEPA filter delivering 12 air changes per hour. Because the ward had been refurbished with antimicrobial devices, including plasma air treatment, which had not yet been activated, it was decided to test the effect of activating the plasma air treatment of bioaerosols. The Plasma treatment devices (Novaerus) are designed to achieve electrostatic precipitation of airborne particles into the proximity of an electrical plasma generator coil [6] . Discharge from the coil generates localised electrons, ions, reactive radicals, and ultraviolet light which are thought to underly inactivation of airborne bacteria, fungi and viruses observed in vitro with the device [7] .

Bacterial numbers cultured using air and surface sampling would be assessed. A period of at least 14 days observations without plasma treatment was compared with a period of at least 14 days with plasma treatment.

The study was carried out in a 4-bedded bay with impaction and settle plate samples taken during twice daily visits to the ward Monday -Friday over a total of 28 days. Samples were taken at 2 timepoints 11:30 and 13:00 at locations ~1 m off the floor. A MAS-100 ® microbial air sampler (MERCK, Germany) was operated with an air intake of 100 L/min for 1 minute, and settle plates left for 1 hour. Bacterial counts were assessed using tryptic soy agar (TSA) and fungal loads using Sabouraud Dextrose Agar (SDA) in 90 mm petri dishes and plates were incubated at 30°C for 5 days. Cotton swabs were used, and surface swabbing was carried out daily at specific sites not touched by patients or subject to daily cleaning ( Fig.1 ).

Swab site 1 was a horizontal shelf at a height of 1.8 m, swab site 2 was a horizontal plastic surface at a height of 1.5 m and swab site 3 was a vertical, metal sliding door housing 2 m outside the entrance to the bay. Swab tips were wetted in sterile water and applied to a 10 cm 2 area before streaking onto TSA and SDA agar plates. Bacterial counts were assessed using TSA and fungal loads using SDA in 90 mm petri dishes and plates were incubated at 30 °C for 5 days. Curam Medical (Dublin, Ireland) performed colony counts on coded (blinded)

plates.

An IRC5716-NW Gazelle DualView IP Counter 60° Master Unit footfall counter (Axiomatic Technology, Nottingham, UK) was used to continuously monitor footfall in and out of the ward bay. This was located 2.2 m above the bay entrance (Fig.1 ).

Teaching Hospitals Application ECM 4 (b) 07/03/17.

Plasma treatment units comprised one Novaerus NV800 at the bay entrance and four wallmounted NV200 (Novaerus Ltd, Dublin, Ireland), locations marked in Figure 1 , numbers installed advised by the manufacturer. The claimed air passage rates are 220 (NV800) and 80 (NV200) m 3 /hr respectively.

P-values were calculated with a t-test (parametric) or Mann-Whitney U test (non-parametric) using the Benjamini-Hochberg method to control false discovery rate.

There was no significant difference in CFU counts for impaction or settle plate samples for either the 11:30 or the 13:00 sampling intervals between the plasma treatment and control non-treatment period (Table I) . Like the MAS-100 and settle plate samples, the swab samples taken at 3 different areas showed no significant difference for either sampling intervals between the plasma treatment and control non-treatment period. The swabs taken within the ward (swab 1 and swab 2) resulted in higher CFU/m 3 than the swab 3 sample just outside the ward, but the latter was of a vertically oriented metal surface, rather than a horizontal painted or plastic surface. Recorded means, Table I , for swab 1 and swab 2 were higher at 11:30 than 13:00, suggesting that the overnight accumulation was collected with the first 11:30 sample.

The mean and summed half-hourly diurnal footfall counts did not vary between observation periods and no significant difference (P<0.01) was found between plasma treatment and control periods, for any time of day. Mean footfall counts were lowest overnight 00:00 -04:30 and peaked in the mornings at 07:00 (41±10 per half-hour (phh)) with the plasma treatment unit on and at 08:00 (42±15 phh) with the units off. Lesser peaks followed at 11:30 (35±12 phh) and 15:00 (29±12 phh), 13:00 (20±12 phh) and 18:00 (20±9 phh). The consistent diurnal footfall pattern reflected regular ward events where the largest number of staff were active on the ward when the day shift nursing staff (6) (7) (8) (9) arrived for handover at 07:45. Beds were usually made 08:30-10:00.

Footfall counts did not show significant correlation with MAS-100 (r(34) = +0.17, P > 0.05) or settle plate counts (r(34) = +0.05, P > 0.05).

This study characterised the indoor air in a hospital respiratory ward using plate count cultures of air and surface samples over 20 weekdays. Movement activity (known to have a significant effect on indoor air in itself [8] , and a correlate of occupancy) was likewise continuously monitored remotely by an infra-red people counter at the entrance to the bay.

This confirms the practicality of modern monitoring technology in assessment of the hospital environment.

Over the sampling periods the cultures with the MAS-100 varied greatly exhibiting a standard deviation of ± 341 CFU/ m 3 around a mean of 542 CFU/ m 3 (Table I) , similar to high sample variations observed by O'Brien et al. [9] . Likewise, the surface swab samples reported large standard deviations in all sample areas (Table I) .

The effect of activating plasma treatment units on ward air using culture was observed.

Testing of air samples by impact and settle plates found no significant change in CFU counts with plasma treatment at either of the two time points studied, 11:30 and 13:00 (P > 0.01) (Table I) . Similarly, surface swab samples taken from 3 different areas showed no significant difference at any area for either sampling time-intervals between the plasma treatment and control non-treatment period.

Infra-red footfall counts did not correlate with CFU in cultures of samples collected. A previous study of an intensive care unit linking occupancy with airborne bacterial culture numbers [10] required intensive sampling (every 15 minutes for 10 hours), which would be difficult to sustain over a 4-week study.

The data collected during this study does not support efficacy of these plasma air treatment units in disinfection as determined by culture (colony counts). The fact that interval cultures could not detect an air-modifying effect of devices capable of airborne bacterial and fungal inactivation in vitro may be due to the complexity of the hospital environment tested, containing multiple (albeit typical) bioaerosol sources, and including activity-related peaks at the bay entrance. Before concluding that this method of air disinfection is ineffective in this environment, further study involving the use of units with higher air passage rates (m 3 /hr), and a longer study duration of plasma treatment is required.

J o u r n a l P r e -p r o o f 

World Health Organization Report on the burden of endemic health care-associated infection worldwide

Hospital-acquired infection-airborne or not?

World Health Organization. Transmission of SARS-CoV-2: implications for infection prevention precautions: scientific brief

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Effect of a novel air disinfection system on airborne micro-organisms in a hospital outpatient clinic

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