key: cord-0907807-pi77smba authors: Lawton, Tom; Butler, Matt; Peters, Christine title: Airborne protection for staff is associated with reduced hospital-acquired COVID-19 in English NHS Trusts date: 2021-11-30 journal: J Hosp Infect DOI: 10.1016/j.jhin.2021.11.018 sha: cc3da4352c6126f4ff78df9aadcb9b75b31fd977 doc_id: 907807 cord_uid: pi77smba INTRODUCTION: Hospital-acquired infection with COVID-19 (HAI) has reduced from 14.3% to 4.2% over the last year, but substantial differences still exist between English NHS hospital trusts. METHODS: We assessed rates of HAI, comparing NHS hospital trusts using airborne respiratory protection (RPE, eg FFP3 masks) for all staff, as a marker of measures to reduce airborne spread, against those using mostly droplet precautions (eg surgical masks). Results/Discussion: RPE use was associated with a 33% reduction in HAI odds in the Delta wave, and 21% in the Alpha wave (p<0.00001). We recommend all hospitals make airborne mitigations a priority. Hospital-acquired infections (HAIs) are associated with poorer outcomes both for the individual and the wider health care system, and hospital-acquired COVID-19 in the NHS has been a significant driver of the pandemic. 1 National reporting and investigation of other nosocomial infections have led to a significant reduction in rates, 2 but for COVID-19 there has been little central work to understand the large variation between NHS hospital trusts. Over the last 18 months there has been substantial development in the understanding of airborne transmission, asymptomatic spread, PPE use, and regular testing for patients and staff. [3] [4] [5] UK NHS hospital trusts have common guidance as to COVID-19 pathways and isolation, 6 but resources and implementation vary between trusts. The improvements and variation still seen suggest that nosocomial spread of COVID-19 is not inevitable, but the question remains as to how best to reduce rates and keep them low. 2020 guidance stated that COVID-19 was spread by the droplet route except for a list of "aerosol generating procedures" ("AGPs"); changes in 2021 acknowledge airborne transmission but state that only droplet precautions are required for healthcare staff unless a local risk assessment suggests otherwise. 6 Some NHS hospital trusts have nevertheless chosen to protect staff against airborne transmission by allowing the use of respiratory protective equipment (RPE, eg FFP3 masks) for all staff caring for patients with COVID-19. Early in 2020, shortages of personal protective equipment (PPE) may have limited the opportunity to use higher levels of protection, but by summer 2020 PPE supplies had improved. 7 Our hypothesis is that this acceptance of airborne transmission, and the mitigation measures it entails, is associated with a reduction in the nosocomial transmission of COVID-19. Hospital-acquired COVID-19 was calculated as "probable" or "definite" hospital-acquired infections from NHS England weekly COVID-19 statistics, defined as COVID-19 diagnoses made 8 or more days after hospital admission, and before hospital discharge. The first available data were from 1st August 2020; data were separated into waves -"Alpha" from 1st August 2020 to 30th April 2021, and "Delta" from 1st May 2021 onwards. Data was downloaded from NHS England on 16th September 2021, and the last data point was 12th September 2021. The rate of hospital-acquired infection with COVID-19 ("HAI rate") was calculated as a percentage of total COVID-19 cases for each NHS hospital trust. Hospital size was calculated from NHS England overnight bed data, as the average number of acute hospital beds open overnight from July to September 2020. Hospital COVID-19 pressure was calculated as the total number of COVID-19 patients treated per acute hospital bed. RPE use was from a public dataset maintained by FreshAirNHS, compiled from news reports, public statements, and private communication. All NHS hospital trusts recorded as using RPE were contacted on 20th September 2021 to confirm their current practice, and an open call was made to other trusts who may have been missing from the dataset to come forward. For each wave in the data, an NHS hospital trust was marked as using RPE if at any point during the wave it was recorded as allowing staff to use RPE when caring for patients with COVID-19 outside the setting of "AGPs". Data were analysed in R 4.0.4 (R Core Team). Significance testing used the exact 2x2 test for patient-level analysis, and Wilcoxon rank-sum test for NHS hospital trust-level analysis. Correlations were calculated as Spearman's rank correlation coefficient. Data used in this analysis are publicly available and accompany this article. HAI rates Results for NHS hospital trust-level and patient-level analyses are given in Table 1 , and overall NHS hospital trust-level rates are shown in Figure 1 . A time series analysis of HAI rates across all acute NHS hospital trusts shows a large peak in December 2020 with average HAI rates over 20%, followed by improvement to June 2021, corresponding with the rollout of vaccines in the UK. However in this present wave up to September 2021, rates are again increasing. Discussion RPE use for all COVID-19 facing staff by English NHS hospital trusts is associated with a significant reduction in hospital-acquired COVID-19. Whilst we have used RPE use outside "AGPs" as a marker, we consider the results likely to be due to a multimodal series of interventions directed against airborne transmission in NHS hospital trusts which have prioritised action in this way. The reduction in HAI rates demonstrated is greater than would be expected directly from RPE use i.e. by preventing asymptomatically infected health care workers infecting patients, reported as 9%. 8 The data presented demonstrate that the measures associated with RPE implementation, likely involving improvements to ventilation and air filtration, are associated with a 21% and 33% relative reduction in odds of hospital-acquired COVID-19 for the Alpha and Delta waves respectively. We have made efforts to have accurate data on RPE use; it is possible that we are unaware of some NHS hospital trusts using RPE officially or unofficially. This would tend to reduce the effect size so our results may underestimate the true impact. Our findings are in keeping with modelling suggesting that screening and effective PPE use are effective interventions to reduce nosocomial COVID-19 transmission. 9 Our finding that high NHS hospital trust COVID-19 pressure was associated with lower HAI rates is novel, but the effect size is relatively small and is potentially because a high COVID-19 occupancy means there are few patients without COVID-19 able to catch it. It also suggests that community rates are not the main driver of hospital-acquired COVID-19 once considered as a percentage of cases. Our combined patientlevel and NHS hospital trust-level analyses ensure that small hospitals having large outbreaks do not skew the analysis, but care must be taken in interpretationthe patient level numbers do not represent risk for a COVID-19 negative patient subsequently catching it in hospital, but the proportion of COVID-19 positive patients in hospital who probably caught it there. The greater relative reduction in HAI rates seen with the Delta wave in NHS hospital trusts implementing RPE likely reflects the underlying hierarchy of controls being more effective from April 2021, coinciding with updates to national infection prevention and control guidance which emphasised their use. 6 In the later wave, NHS hospital trusts were seemingly better able to isolate cases through enhanced staff and patient testing, achieving reductions in HAI rates in all trusts irrespective of airborne mitigations. Once all NHS hospital trusts are appropriately implementing the hierarchy, this increased homogeneity would cause differences like airborne mitigations to have a larger relative effect on reducing nosocomial transmission. At the peak in December 2020, high HAI rates could have been driven by a variety of factors including overcrowding as England's COVID-19 hospitalisations rose rapidly, leading to a breakdown in the ability to cohort patients. The drop in HAI at the January peak of hospitalisations may have represented the early vaccine rollout, other mitigations, or simply there being fewer patients without COVID-19 in the hospitals to catch it. Whilst vaccines and other mitigations have reduced rates of hospital-acquired COVID-19, there is room for improvement as further mitigations directed against airborne transmission are rolled out. Whilst it is relatively quick to deploy FFP3 respirators outside of AGP areas, it is much slower to audit ventilation and deploy air filtration units, and even slower to upgrade hospital estates to include more side rooms including negative pressure isolation rooms. However it is important to recognise that even hospitals with majority side room provision have still seen nosocomial spread (personal communication, C Peters), The potential role of ventilation and air flows in these types of wards is in keeping with detailed investigations of quarantine hotel outbreaks in Australia. Recent data highlight that over 4% of hospital COVID-19 cases are still nosocomial, and by only including patients who became positive after more than 7 days this is likely to be an underestimate particularly for Delta, where the peak of infectivity is earlier than previous lineages. 10 Also, patients who have acquired infection but are not yet shedding the virus by their last test before discharge will likewise not be counted; this is a limitation of our underlying data. Equally, healthcare workers themselves have been at risk of contracting COVID-19 in hospitals and this is not covered by our data; other work has shown that airborne mitigations can reduce the risk to staff. 4 The time series data show that COVID-19 HAI rates have been worsening since July 2021, lending an urgency to finding ways to further improve. SAGE advice from early 2021 suggests a range of ways to mitigate airborne transmission of COVID-19 in hospitals, and more general advice has existed longer. 11 We recommend all hospitals to adopt appropriate airborne aerosol mitigations to protect staff and patients. Scientific Advisory Group for Emergencies. PHE and LSHTM: The contribution of nosocomial infections to the first wave Great Britain, Parliament H of C. Reducing healthcare associated infections in hospitals in England: report Ten scientific reasons in support of airborne transmission of SARS-CoV-2 Efficacy of FFP3 respirators for prevention of SARS-CoV-2 infection in healthcare workers Screening of healthcare workers for SARS-CoV-2 highlights the role of asymptomatic carriage in COVID-19 transmission COVID-19 infection prevention and control guidance -Version 1.2. London: PHE; 2021 The supply of personal protective equipment (PPE) during the COVID-19 pandemic. London: National Audit Office Superspreaders drive the largest outbreaks of hospital onset COVID-19 infections Interventions to control nosocomial transmission of SARS-CoV-2: a modelling study Viral infection and transmission in a large, well-traced outbreak caused by the SARS-CoV-2 Delta variant How can airborne transmission of COVID-19 indoors be minimised?