Magnetic resonance imaging respirators: a randomized crossover trial to assess respiratory protection, usability, and comfort.

Objective: Many available facepiece filtering respirators contain ferromagnetic components, which may cause significant problems in the magnetic resonance imaging (MRI) environment. We conducted a randomized crossover trial to assess the effectiveness, usability, and comfort of 3 types of respirators, judged to be "conditionally MRI safe" with an aluminum nosepiece (Halyard 46727 duckbill-type respirators and Care Essentials MSK-002 bifold cup-type respirators) or "MRI safe" completely metal free (Eagle AG2200 semirigid cup-type respirators). Design and setting: We recruited 120 participants to undergo a quantitative fit test (QNFT) on each of the 3 respirators in a randomized order. Participants then completed a usability and comfort assessment of each respirator. Results: There were significant differences in the QNFT pass rates (51% for Halyard 46727, 73% for Care Essentials MSK-002, and 86% for Eagle AG2200, P < .001). The first-time fit test pass rate and overall fit factor were significantly higher for Eagle AG2200 compared with the other 2 respirators. Eagle AG2200 scored the lowest ratings in the ease of use and overall comfort. There were no significant differences in other modalities, including the seal rating, breathability, firmness, and overall assessment. Conclusions: Our study supports the utility of the Eagle AG2200 and Care Essentials MSK-002 respirators for healthcare professionals working in an MRI environment, based on their high QNFT pass rates and reasonably good overall usability and comfort scores. Eagle AG2200 is unique because of its metal-free construction. However, its comparatively lower usability and comfort ratings raise questions about practicality, which may be improved by greater user training.

Development of a rapid, multi-organisational, multi-modal assessment of a newly available disposable respirator.

BACKGROUND: A rapid large-scale evaluation of a newly available duckbill style P2/N95 respirator, the Care Essentials (CE) MSK-003, was required to determine its suitability for deployment into the Victorian healthcare service. The aims of this study were to assess the feasibility of establishing a rapid, multi-organisational and multi-modal evaluation of the respirator, and to investigate whether this respirator would meet the needs of healthcare workers. METHODS: The evaluation was a collaboration among three healthcare organisations - two tertiary hospitals in metropolitan Melbourne and a rural-based hospital. Participants were healthcare workers undertaking their routine fit tests. They were required to complete quantitative fit testing and a usability assessment survey on the CE MSK-003 respirator. The a priori performance criteria were set as fit test pass rate of >70%, plus satisfactory subjective overall comfort and performance assessments, defined as a rating of adequate, good, or very good in >90% of the cohort. RESULTS: A total of 1070 participants completed the multi-modal assessment within a month. Seventy-eight percent of participants passed their quantitative fit test. Over 90% of survey respondents reported that the CE MSK-003 was adequate, good or very good in terms of its overall comfort and performance assessments. CONCLUSION: We demonstrated that a multi-modal evaluation of a new respirator can be rapidly conducted with a high level of participation in a controlled, consistent manner across multiple organisations. The evaluation results of the CE MSK-003 respirator exceeded our predetermined (a priori) minimal criteria, making it suitable for broad distribution to healthcare organisations.

Prospective comprehensive evaluation of an elastic-band beard cover for filtering facepiece respirators in healthcare workers.

OBJECTIVE: To undertake a healthcare-based multimodal evaluation of the combination of filtering facepiece respirator (FFR) with the elastic-band beard cover technique, including quantitative fit test (QNFT) results, skills assessment, and usability assessment. DESIGN AND SETTING: We conducted a prospective study through the Respiratory Protection Program at the Royal Melbourne Hospital from May 2022 to January 2023. PARTICIPANTS: Healthcare workers who required respiratory protection and could not shave for religious, cultural, or medical reasons. INTERVENTION: Online education and personal face-to-face training on the use of FFR with the elastic-band beard cover technique. RESULTS: Among 87 participants (median beard length 38 mm; interquartile range [IQR], 20-80), 86 (99%) passed 3 QNFTs consecutively with the elastic-band beard cover under a Trident P2 respirator and 68 (78%) passed 3 QNFTs consecutively with a 3M 1870+ Aura respirator. The first QNFT pass rate and the overall fit factors were significantly higher when using the technique than without the elastic-band beard cover. Most participants displayed a high skill level in their donning, doffing, and user seal-check techniques. Of 87 participants, 83 (95%) completed the usability assessment. The overall ease of use, comfort, and overall assessment were rated highly. CONCLUSIONS: The elastic-band beard cover technique can provide safe and effective respiratory protection for bearded healthcare workers. The technique was easily taught, comfortable, well tolerated and accepted by healthcare workers, potentially allowing them full participation in the workforce during pandemics with airborne transmission. We recommend further research and evaluation of this technique in a broader health workforce.

Effects of surfactant head group modification on vertically oriented mesoporous silica produced by the electrochemically assisted surfactant assembly method.

Production of mesoporous silica films with vertically oriented pores has been a challenge since interest in such systems developed in the 1990s. Vertical orientation can be achieved by the electrochemically assisted surfactant assembly (EASA) method using cationic surfactants such as cetyltrimethylammonium bromide (C16TAB). The synthesis of porous silicas using a series of surfactants with increasing head sizes is described, from octadecyltrimethylammonium bromide (C18TAB) to octadecyltriethylammonium bromide (C18TEAB). These increase pore size, but the degree of hexagonal order in the vertically aligned pores reduces as the number of ethyl groups increases. Pore accessibility is also reduced with the larger head groups.

Post-surgical discharge opioid prescribing, use and handling after introduction of a stewardship program.

SummaryOpioids are often used to provide postsurgical analgesia but may cause harm if used inappropriately. We introduced an opioid stewardship program in three Melbourne hospitals to reduce the inappropriate use of opioids after patient discharge. The program had four pillars: prescriber education, patient education, a standardised quantity of discharge opioids, and general practitioner (GP) communication. Following introduction of the program, we undertook this prospective cohort study. The study aimed to describe post-program discharge opioid prescribing, patient opioid use and handling, and the impact of patient demographics, pain and surgical treatment factors on discharge prescribing. We also evaluated compliance with the program components. We recruited 884 surgical patients from the three hospitals during the ten-week study period. Discharge opioids were dispensed to 604 (74%) patients, with 20% receiving slow-release opioids. Junior medical staff undertook 95% of discharge opioid prescribing, which was guideline-compliant for 78% of patients. Of the patients discharged with opioids, a GP letter was sent for only 17%. Follow-up at two weeks was successful in 423 (70%) patients and in 404 (67%) at three months. At the three-month follow-up, 9.7% of patients reported ongoing opioid use; in preoperatively opioid naïve patients, the incidence was 5.5%. At the two-week follow-up, only 5% reported disposal of excess opioids, increasing to 26% at three months. Ongoing opioid therapy at three months in our study cohort (9.7%; 39/404) was associated with preoperative opioid consumption and higher pain scores at the three-month follow-up. The introduction of the opioid stewardship program resulted in highly guideline-compliant prescribing, but hospital-to-GP communication was uncommon and opioid disposal rates were low. Our findings suggest that opioid stewardship programs can improve postoperative opioid prescribing, use and handling, but the realisation of these gains will require effective program implementation.

Correct specific retention volume determination in inverse gas chromatography.

Inverse Gas Chromatography (IGC) is an important technique for characterization of solids. Determining the specific retention volume of the injected probe molecule is the basis of the analysis for all the physico-chemical properties that the technique can determine, most importantly in Heat of Sorption, Glass Transition Temperature, Gibbs Adsorption Free Energy. Two equations have been used in the literature to calculate the specific retention volume; one normalizes the retention volume to 0 °C (standard temperature), which was previously proven to be thermodynamically incorrect, while the other calculates the retention volume at the measurement temperature. Here, we compare the heat of sorption for a series of alkanes on two substrates, micro crystalline cellulose and natural graphite, calculated using these two equations. This study shows that the specific retention volume is strongly dependent on the column temperature. Using the retention volume values normalised to 0 °C consistently overestimates the heats of sorption by up to 10%. Most importantly, correcting the retention volume to standard temperature will misrepresent the effect of temperature on the retention volume and the thermodynamic parameters derived from it.

Assessment of Safety of a Fully Implanted Endovascular Brain-Computer Interface for Severe Paralysis in 4 Patients: The Stentrode With Thought-Controlled Digital Switch (SWITCH) Study.

Importance: Brain-computer interface (BCI) implants have previously required craniotomy to deliver penetrating or surface electrodes to the brain. Whether a minimally invasive endovascular technique to deliver recording electrodes through the jugular vein to superior sagittal sinus is safe and feasible is unknown. Objective: To assess the safety of an endovascular BCI and feasibility of using the system to control a computer by thought. Design, Setting, and Participants: The Stentrode With Thought-Controlled Digital Switch (SWITCH) study, a single-center, prospective, first in-human study, evaluated 5 patients with severe bilateral upper-limb paralysis, with a follow-up of 12 months. From a referred sample, 4 patients with amyotrophic lateral sclerosis and 1 with primary lateral sclerosis met inclusion criteria and were enrolled in the study. Surgical procedures and follow-up visits were performed at the Royal Melbourne Hospital, Parkville, Australia. Training sessions were performed at patients' homes and at a university clinic. The study start date was May 27, 2019, and final follow-up was completed January 9, 2022. Interventions: Recording devices were delivered via catheter and connected to subcutaneous electronic units. Devices communicated wirelessly to an external device for personal computer control. Main Outcomes and Measures: The primary safety end point was device-related serious adverse events resulting in death or permanent increased disability. Secondary end points were blood vessel occlusion and device migration. Exploratory end points were signal fidelity and stability over 12 months, number of distinct commands created by neuronal activity, and use of system for digital device control. Results: Of 4 patients included in analyses, all were male, and the mean (SD) age was 61 (17) years. Patients with preserved motor cortex activity and suitable venous anatomy were implanted. Each completed 12-month follow-up with no serious adverse events and no vessel occlusion or device migration. Mean (SD) signal bandwidth was 233 (16) Hz and was stable throughout study in all 4 patients (SD range across all sessions, 7-32 Hz). At least 5 attempted movement types were decoded offline, and each patient successfully controlled a computer with the BCI. Conclusions and Relevance: Endovascular access to the sensorimotor cortex is an alternative to placing BCI electrodes in or on the dura by open-brain surgery. These final safety and feasibility data from the first in-human SWITCH study indicate that it is possible to record neural signals from a blood vessel. The favorable safety profile could promote wider and more rapid translation of BCI to people with paralysis. Trial Registration: ClinicalTrials.gov Identifier: NCT03834857.

Protocol of a prospective comprehensive evaluation of an elastic band beard cover for filtering facepiece respirators in healthcare.

Individuals who are unable to be clean shaven for religious, medical or cultural reasons are unable to wear a filtering facepiece respirator (FFR), as the respirator cannot provide adequate protection against aerosol-transmissible diseases. There is currently a paucity of validated techniques to ensure the safe inclusion of bearded healthcare workers in the pandemic workforce. We propose to undertake a healthcare-based multi-modal evaluation study on the elastic band beard cover for FFR technique, examining the quantitative fit test (QNFT) results, usability and skill level of participants with repeated assessments over time. This is a prospective study conducted through the Respiratory Protection Program at the Royal Melbourne Hospital. Healthcare workers are invited to participate if they require respiratory protection and cannot shave for religious, cultural or medical reasons. An online education package on the use of respiratory protective equipment and the elastic band beard cover for FFR technique is provided. This is followed by a face-to-face session, where the participant will receive: one-on-one training; undergo a skill assessment on their donning, doffing and user seal check techniques; complete QNFTs and a usability survey. Participants will be invited to repeat the assessment within 3 months of the first session and at 12 months. This study involves multimodal and repeated assessments of an elastic band beard cover for FFRs. The findings of this study will provide information on: whether this simple technique can provide safe, consistent and effective respiratory protection; whether it will interfere with occupational activities; and whether it is comfortable and tolerable for the duration of wear. This is of significant importance to the health workforce around the world, who cannot shave but require access to respiratory protective equipment during the COVID-19 pandemic.

Quantitative fit-test concordance of a pair of similar-fit 3M Aura respirator models, 3M 9320A+ and 3M 1870+: A randomized crossover study.

OBJECTIVE: Some manufacturers provide information on similar-fit model pairings of filtering facepiece respirators (FFRs), suggesting that fit-test outcome of one model helps predict the other. This guidance may be useful during crisis capacity when FFR supplies and/or fit tests are constrained. The purpose of this study was to compare quantitative fit-test (QNFT) results and concordance between a pair of similar-fit 3M Aura FFRs: the 3M 9320A+ and 3M 1870+. METHODS: All participants completed online training and a QNFT with both respirators. The order of the respirator being examined first was randomly allocated. The outcomes included QNFT pass rate, concordance between the 2 models, overall and individual fit factors, and percentage of male and female participants who passed or failed the QNFT. RESULTS: We recruited 1,000 participants (668 females and 332 males). The QNFT pass rate, overall fit factors, and individual fit factors were significantly higher for the 3M 9320A+ than the 3M 1870+ FFR. The concordance between the models was "fair" (κ coefficient, 0.38). Male participants who passed a QNFT with either of the FFRs had 96% chance of passing the QNFT for the alternate model. Female participants who passed the 3M 1870+ had 97% chance of passing the QNFT for the 3M 9320A+ model. However, ∼1 in 12 females who passed the QNFT for the 3M 9320A+ failed the QNFT for the 3M 1870+ FFR. CONCLUSIONS: Similar-fit paired FFR models may provide a consequentially different level of respiratory protection, especially for women. Our findings are important for FFR stockpiling and fit-testing strategies, especially during crisis capacity.

HALO CleanSpace PAPR evaluation: Communication, respiratory protection, and usability.

OBJECTIVE: To evaluate a relatively new half-face-piece powered air-purifying respirator (PAPR) device called the HALO (CleanSpace). We assessed its communication performance, its degree of respiratory protection, and its usability and comfort level. DESIGN AND SETTING: This simulation study was conducted at the simulation center of the Royal Melbourne Hospital. PARTICIPANTS: In total, 8 voluntary healthcare workers participated in the study: 4 women and 4 men comprising 3 nursing staff and 5 medical staff. METHODS: We performed the modified rhyme test, outlined by the National Institute for Occupational Safety and Health (NIOSH), for the communication assessment. We conducted quantitative fit test and simulated workplace protection factor studies to assess the degree of respiratory protection for participants at rest, during, and immediately after performing chest compression. We also invited the participants to complete a usability and comfort survey. RESULTS: The HALO PAPR met the NIOSH minimum standard for speech intelligibility, which was significantly improved with the addition of wireless communication headsets. The HALO provided consistent and adequate level of respiratory protection at rest, during and after chest compression regardless of the device power mode. It was rated favorably for its usability and comfort. However, participants criticized doffing difficulty and perceived communication interference. CONCLUSIONS: The HALO device can be considered as an alternative to a filtering face-piece respirator. Thorough doffing training and mitigation planning to improve the device communication performance are recommended. Further research is required to examine its clinical outcomes and barriers that may potentially affect patient or healthcare worker safety.

Human-machine collaboration using artificial intelligence to enhance the safety of donning and doffing personal protective equipment (PPE).

OBJECTIVES: To compare the accuracy of monitoring personal protective equipment (PPE) donning and doffing process between an artificial intelligent (AI) machine collaborated with remote human buddy support system and an onsite buddy, and to determine the degree of AI autonomy at the current development stage. DESIGN AND SETTING: We conducted a pilot simulation study with 30 procedural scenarios (15 donning and 15 doffing, performed by one individual) incorporating random errors in 55 steps. In total, 195 steps were assessed. METHODS: The human-AI machine system and the onsite buddy assessed the procedures independently. The human-AI machine system performed the assessment via a tablet device, which was positioned to allow full-body visualization of the donning and doffing person. RESULTS: The overall accuracy of PPE monitoring using the human-AI machine system was 100% and the overall accuracy of the onsite buddy was 99%. There was a very good agreement between the 2 methods (κ coefficient, 0.97). The current version of the AI technology was able to perform autonomously, without the remote human buddy's rectification in 173 (89%) of 195 steps. It identified 67.3% of all the errors independently. CONCLUSIONS: This study provides preliminary evidence suggesting that a human-AI machine system may be able to serve as a substitute or enhancement to an onsite buddy performing the PPE monitoring task. It provides practical assistance using a combination of a computer mirror, visual prompts, and verbal commands. However, further studies are required to examine its clinical efficacy with a diverse range of individuals performing the donning and doffing procedures.

The psychological impact on perioperative healthcare workers during Victoria's second COVID-19 wave: A prospective longitudinal thematic analysis.

The COVID-19 pandemic has had a profound psychological impact on our frontline healthcare workers. Throughout the entire second COVID-19 wave at one major tertiary hospital in Melbourne Australia, longitudinal qualitative data between perioperative staff members, and analyses of intrapersonal changes were reported. Inductive analysis of three open-ended questions generated four major themes: Organisational Response to the Pandemic, Psychological Impact, Changes in Feelings of Support Over Time and Suggestions for Changes. Understanding the challenges, perception and suggestions from this longitudinal study allows us to provide a range of support services and interventions to minimise the long-term negative psychological impact and be better prepared should another similar situation arises again.

Optimizing twin sampling tube stabilization improves quantitative fit test results for flat-fold duckbill filtering facepiece respirators.

INTRODUCTION: When performing quantitative fit testing (QNFT) on filtering facepiece respirators using an ambient aerosol technique, a twin sampling tube is connected between the condensation nuclei count machine and the probed respirator. To achieve high quality and repeatable QNFT results, robust sampling tube stabilization is required. METHODS: In this prospective randomized crossover study, conducted in December 2021 to February 2022, we compared the commonly used hand-hold technique with the manufacturer-recommended lanyard technique in stabilizing the sampling tube during QNFT on a Halyard N95 respirator. Outcomes included QNFT pass rates, overall and individual fit factors, and concordance between the two techniques. RESULTS: A total of 228 out of 316 participants (72.2%) passed the QNFT with the hand-hold technique, compared to the lanyard technique (166/316, 52%, P < .001). The most significant drop in the fit factors with the lanyard technique occurred during head movement side-to-side and up-and-down. The concordance between the 2 techniques was fair (Kappa coefficient = 0.39). CONCLUSION: Our study demonstrates that the method of sampling tube stabilization during QNFT has a significant impact on fit test pass rates, with a potential for false negative fit tests due to inadequate tube stabilization. Further research is required to examine the generalizability of these results to other respirators and fit testing apparatuses.

Prediction of peptides retention behavior in reversed-phase liquid chromatography based on their hydrophobicity.

Hydrophobicity is an important physicochemical property of peptides and proteins. It is responsible for their conformational changes, stability, as well as various chemical intramolecular and intermolecular interactions. Enormous efforts have been invested to study the extent of hydrophobicity and how it could influence various biological processes, in addition to its crucial role in the separation and purification endeavor as well. Here, we have reviewed various studies that were carried out to determine the hydrophobicity starting from (i) simple amino acids solubility behavior, (ii) experimental approach that was undertaken in the reversed-phase liquid chromatography mode, and ending with (iii) some examples of more advanced computational and machine learning models.

A randomised crossover trial of two flat-fold cup respirators: BYD DE2322 N95 versus Care Essentials MSK-002 P2.

BACKGROUND: The use of respiratory protection remains important in protecting health care workers from airborne pathogens such as viruses. Respirator supply is constantly changing with new models regularly becoming available. Health services should consider a broad range of factors when procuring respirators, including the results of quantitative fit testing in a representative sample of the workforce. Subjective comfort factors and compatibility with a variety of workplace tasks, such as suitability for staff use near magnetic resonance imaging (MRI) environments where relevant, should also be considered. This article compares the quantitative fit factors and user assessments for two styles of flat-fold cup respirators, Care Essentials (CE) MSK-002 P2 and BYD DE2322 N95. METHODS: Quantitative fit tests (QNFT) were performed on 300 participants on each model of respirator in this randomised crossover trial. Participants then completed a questionnaire on their assessments of each respirator. RESULTS: The Care Essentials MSK-002 had a significantly higher quantitative fit test pass rate than the BYD DE2322 (57% vs 18%, p < 0.001). There was no concordance between fit test pass rates for each model. Additionally, the Care Essentials MSK-002 achieved significantly higher scores on each of the responses in the subjective usability survey. CONCLUSION: It is recommended that the Care Essentials MSK-002 be made available for health care use due to higher QNFT pass rates, higher subjective usability assessment scores, plus its potential for use in MRI environments when compared to the BYD DE2322.

Successful synthesis of a glial-specific blood-brain barrier shuttle peptide following a fragment condensation approach on a solid-phase resin.

Successful manual synthesis of the TD2.2 peptide acting as a blood-brain barrier shuttle was achieved. TD2.2 was successfully synthesised by sequential condensation of four protected peptide fragments on solid-phase settings, after several unsuccessful attempts using the stepwise approach. These fragments were chosen to minimise the number of demanding amino acids (in terms of coupling, Fmoc removal) in each fragment that are expected to hamper the overall synthetic process. Thus, the hydrophobic amino acids as well as Arg(Pbf) were strategically spread over multiple fragments rather than having them congested in one fragment. This study shows how a peptide that shows big challenges in the synthesis using the common stepwise elongation methodology can be synthesised with an acceptable purity. It also emphasises that choosing the right fragment with certain amino acid constituents is key for a successful synthesis. It is worth highlighting that lower amounts of reagents were required to synthesise the final peptide with an identical purity to that obtained by the automatic synthesiser.

Greener Cleavage of Protected Peptide Fragments from Sieber Amide Resin.

Following the successful introduction of two benign solvents for cleaving protected acid peptide fragments from 2-chlorotrityl chloride (2-CTC) resin, there is a need to green the cleavage process for obtaining protected peptide amide fragments. In this work, p-xylene and toluene are introduced as greener alternates to dichloromethane (DCM) for preparing protected peptide amide fragments from a Sieber amide resin. The N-dealkylation is a demanding chemical reaction, requiring that the cleavage protocol be optimised to ensure complete cleavage from the resin. After a 30 min reaction time, only 66 % of the final peptide product was retrieved even with the conventional dichloromethane solvent. Therefore, 120 min was considered sufficient to fully cleave the peptide from the Sieber amide resin. This work reaffirms the fact that greening strategies are far from detrimental, with green alternatives often outperforming their replaced counterparts.

Influence of Tie-Molecules and Microstructure on the Fluid Solubility in Semicrystalline Polymers.

Predicting the absorption of gases and liquids in semicrystalline polymers is of critical importance for numerous applications; the mechanical and transport properties of these materials are highly dependent on the amount of solutes dissolved in their bulk. For most semicrystalline polymers which are in contact with an external fluid, the observed uptake of the solute is found to be lower than that predicted by treating the amorphous domains of the polymer as subcooled polymer melts at the same thermodynamic state. This observation has recently led to the hypothesis that the amorphous domains effectively behave as polymer liquids subject to an additional "constraint pressure" which reduces the equilibrium solubility in the domains. We present a new statistical mechanical model of semicrystalline polymers. The constraint pressure emerges naturally from our treatment, as a property of the interlamellar amorphous domains caused by the stretching and localization in space of the tie-molecules (polymer chains linking different lamellae). By assuming that the interlamellar domains exchange monomers reversibly with the lamellae, the model allows one to simultaneously predict the increase of constraint pressure at low temperatures and the variation of the lamellar thickness as a function of temperature─a phenomenon known as premelting. The sorption isotherms of a range of fluids in different polyethylene and polypropylene samples are determined experimentally and the data is compared with calculations of the new model using the SAFT-VR Mie EoS. In order to accurately predict the absorption close to the vapor pressure of the penetrant, we find that it is essential to include the "free", unconstrained amorphous domains in the description, resulting in a multiscale model with two adjustable parameters (the fractions of tie-molecules and free amorphous domains) that characterize the morphology of a given semicrystalline polymer sample. The trends observed for the adjusted parameters qualitatively match other estimates reported in the literature.

Strategies for Improving Peptide Stability and Delivery.

Peptides play an important role in many fields, including immunology, medical diagnostics, and drug discovery, due to their high specificity and positive safety profile. However, for their delivery as active pharmaceutical ingredients, delivery vectors, or diagnostic imaging molecules, they suffer from two serious shortcomings: their poor metabolic stability and short half-life. Major research efforts are being invested to tackle those drawbacks, where structural modifications and novel delivery tactics have been developed to boost their ability to reach their targets as fully functional species. The benefit of selected technologies for enhancing the resistance of peptides against enzymatic degradation pathways and maximizing their therapeutic impact are also reviewed. Special note of cell-penetrating peptides as delivery vectors, as well as stapled modified peptides, which have demonstrated superior stability from their parent peptides, are reported.

N95 respirators: quantitative fit test pass rates and usability and comfort assessment by health care workers.

OBJECTIVES: To compare the performance of four N95 respirator types with respect to quantitative fit test pass rate and health care worker-rated usability and comfort. DESIGN, SETTING, PARTICIPANTS: Health care workers who participated in the respiratory protection program at the Royal Melbourne Hospital, 1 October 2020 - 31 May 2021. Participants underwent quantitative N95 respirator fit testing (at least three of four types: semi-rigid cup, flat-fold cup, duckbill, and three-panel flat-fold types), and were invited to complete an online usability and comfort assessment for respirators for which their fit test results were passes. MAIN OUTCOME MEASURES: Fit test pass rate, and user-rated overall comfort and assessment ratings (five-point Likert scales), by N95 respirator type. RESULTS: A total of 2161 health care workers underwent quantitative fit testing (women, 1586 [73.4%]; nurses, 1271 [58.8%]). The overall fit test pass rates were 65.0% for the semi-rigid cup respirators (1029/1583 tests), 32.4% for the flat-fold respirator (660/2035 tests), 59.2% for the duckbill respirators (2005/3387 tests), and 96.4% for the three-panel flat-fold respirator (1876/1946 tests). 378 health care workers completed the comfort and usability survey. Overall comfort and assessment ratings each differed by respirator group (P < 0.001); the median overall comfort (4; IQR, 3-4) and overall assessment values (4; IQR, 3-5) were highest for the three-panel flat-fold respirator and lowest for the semi-rigid cup respirators (comfort: 2 [IQR, 1-3]; assessment: 2 [IQR, 2-3]). CONCLUSIONS: The three-panel flat-fold N95 respirator outperformed the three alternative types with regard to fit test pass rate and user-rated comfort and usability. To maximise respiratory protection for health care workers, these factors should be considered when making respirator procurement decisions.