Oxygenation failure recalcitrant to increasing positive end-expiratory pressure is a feature of severe coronavirus disease 2019 (COVID-19) pneumonia [1]. A Chinese group used prone positioning to improve oxygenation for intubated patients with severe COVID-19 pneumonia [2]. However, prone positioning in unconscious patients is labour-intensive and is associated with various complications [3, 4]. As the incidence of severe COVID-19 pneumonia worldwide increases rapidly, many countries are also facing the problem of diminishing intensive care resources. Prone positioning ventilation is most used today in intensive care units (ICU) for patients with acute respiratory distress syndrome (ARDS) [5-7] and for prevention of ventilator-induced lung injury [8, 9]. Many mechanisms have been proposed, including relieving the dependent lung regions from the compressive force of the heart's weight [10] or increasing aeration in the originally dorsal lung regions [11]. The overall lung ventilation from dorsal to ventral areas is more homogeneous in the prone position than in the supine position. Prone positioning thus improves oxygenation whilst the other variable, perfusion, remains almost constant in both postures.

Background: The risk of environmental contamination by SARS-CoV-2 in the intensive care unit (ICU) is unclear. We aimed to evaluate the extent of environmental contamination in the ICU and correlate this with patient and disease factors, including the impact of different ventilatory modalities. Methods: Observational study where surface environmental samples collected from ICU patient rooms and common areas were tested by SARS-CoV-2 PCR, with select samples from the common area tested on cell culture. Clinical data were collected and correlated to presence of environmental contamination. Results were compared to historical data from a previous study in general wards (GW). Results: 200 samples from 20 patient rooms, and 75 samples from common areas and the staff pantry, were tested. 14 rooms had at least one site contaminated, with an overall contamination rate of 14% (28 of 200 samples). Environmental contamination was not associated with day of illness, ventilatory mode, aerosol generating procedures, or viral load. There was lower frequency of environmental contamination in ICU compared to GW rooms. Eight samples from the common area were positive, though all were negative on cell culture. Conclusion: Environmental contamination in the ICU is lower compared to the GW. Use of mechanical ventilation or high-flow nasal oxygen was not associated with greater surface contamination, supporting their use and safety from an infection control perspective. Transmission risk via environmental surfaces in the ICUs is likely to be low. Nonetheless, infection control practices should be strictly reinforced, and transmission risk via droplet or airborne spread remains.

We read with interest the research letter by NG et al. [1], which described their experience in prone positioning (PP) for awake patients with coronavirus disease 2019 (COVID-19) pneumonia, and concluded that this manoeuvre could delay or reduce the need for intensive care. We agree that the authors demonstrated safety and feasibility of PP in COVID-19 pneumonia patients. However, we humbly suggest a few crucial points be addressed before drawing conclusions on the efficacy of PP.