key: cord-0821176-t2j7tq92
authors: Harding, Henry; Broom, Alex; Broom, Jennifer
title: Aerosol generating procedures and infective risk to healthcare workers: SARS-CoV-2 – the limits of the evidence
date: 2020-06-01
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2020.05.037
sha: a99e393babd3c29bc0423f25258e84bdd202e0e3
doc_id: 821176
cord_uid: t2j7tq92

The transmission behaviour of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still being defined. It is likely that it is transmitted predominantly by droplets and direct contact and it is possible that there is at least opportunistic airborne transmission. In order to protect healthcare staff adequately is necessary that we establish whether aerosol generating procedures (AGPs) increase the risk of transmission of SARS-CoV-2. Where we do not have evidence relating to SARS-CoV-2, guidelines for safely conducting these procedures should consider what risk procedures would have of transmitting related pathogens. Currently there is very little evidence detailing the transmission of SARS-CoV-2 associated with any specific procedures. Regarding aerosol generating procedures and respiratory pathogens in general, there is still a large knowledge gap that will leave clinicians unsure what risk they are putting themselves in when offering these procedures. This review aimed to summarise the evidence (and gaps in evidence) around AGPs and SARS-CoV-2.

Since first being reported in December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly spread worldwide. The resulting coronavirus disease of 2019 (COVID- 19) was declared a pandemic by the World Health Organisation in March 2020 [1] . SARS-CoV-2 is considered to primarily be spread by droplet transmission and direct contact [2] [3] . Given the behaviour of similar viruses such as severe acute respiratory syndrome (SARS, also known as SARS-CoV-1), Middle East respiratory syndrome (MERS) and the influenza viruses it is very likely that it can also be spread in an airborne manner by aerosolised particles [4] [5] . It is unclear how significant the role of airborne transmission and transmission related to aerosol generating procedures (AGPs) are in the spread of SARS-CoV-2. This is a knowledge gap that leaves clinicians unsure whether procedures are safe to undertake. Lack of clarity of risk may in turn lead to preventable infections of health care workers if procedures are undertaken without appropriate protection or to worse outcomes for patients if procedures are withheld due to safety concerns. Without specific data relating to SARS-CoV-2, varying guidelines have been established based on general principles and research from SARS and other viruses.

It is likely that there is a hierarchy of AGPs in the sense that they each will convey a different degree of risk of infection transmission. As a result of this, and in the setting of limited evidence, there is disagreement between guidelines as to which procedures should be considered AGPs and how significant the associated infection risk is. Guidelines generally consider at least intubation, pre-intubation ventilation, bronchoscopy, tracheotomy, open airway suctioning, cardiopulmonary resuscitation (CPR) and non-invasive ventilation (NIV) to be AGPs. In some instances administration of nebulised medications, use of high flow nasal canulae (HFNC), use of oxygen masks, nasopharyngeal swabbing and sputum induction are considered AGPs [6] [7] [8] , while other authors have included endoscopy and transoesophageal echocardiography [9] [10] [11] . For these procedures it is generally advised that on top of standard precautions: a patient is isolated in a negative pressure room, procedures are performed by the most skilled operator available, health care workers (HCWs) should always wear gown, gloves and an N95-level mask in the patient room, and that these procedures are only undertaken when absolutely necessary [12] [13] [6] .

The aim of this review is to establish the current understanding of the risk of SARS-CoV-2 infection associated with aerosol generating procedures. Where evidence specific to SARS-CoV-2 is absent, we aimed to determine what conclusions can be made based on data related to other viral infections and to discuss the impact of this knowledge gap and guidelines developed from it.

A review of literature was performed using Pubmed, Embase, the Cochrane library and the World Health Organisation (WHO) COVID-19 database. Searches were made for all papers up until the review date of 1 st of April 2020. Searches were made for: "COVID-19" (and related terms) and "infectivity", "transmission", "airborne" or "aerosol"; "aerosol generating procedures" and "transmission" or "infectivity"; and specific AGPs ("intubation", "tracheostomy", "bronchoscopy", "airway suctioning", "non-invasive ventilation", "high flow nasal canulae", "transoesophageal echocardiography", "endoscopy" or "nebuliser") and "transmission" or "infectivity".

Abstracts were reviewed for relevance and bibliographies of relevant papers were searched for related papers which were subsequently examined. Google search engine was used to identify further literature which was not published in scientific journals and health statistics.

There are no reviews or trials investigating whether AGPs are associated with transmission of SARS-CoV-2. It has been established that there is rapid spread between humans in close proximity and that HCWs may be at increased risk of infection [14] ). In late February 2020 HCWs were reported to comprise only 3.8% of cases in Wuhan [15] , but by late March the Istituto Superiore di Sanita in Italy was reporting HCWs made up nearly 10% of Italian cases [16] . Although this is less than during the SARS outbreak of 2003 (21% HCWs) it is clear that HCWs are at a significant risk at least in some circumstances [17] .

It is not clear to what degree HCWs are being infected despite effective droplet precautions as opposed to those who are infected as a result of inadequate droplet transmission personal protective equipment (PPE). Wang et al. [18] suggest that the considerable number of early healthcare infections and deaths may have been due to a combination of: inadequate PPE due to lack of awareness early in the epidemic, large scale exposure to infected patients, shortage of PPE and inadequate infection prevention training.

There are case reports suggesting airborne transmission may be occurring [2] [19] and it has been shown that SARS-CoV-2 can survive in aerosols at least for 3 hours (with a similar reduction in titre as occurs with SARS-CoV-1) [20] . This doesn't confirm airborne transmission, but it establishes that airborne transmission is feasible and supports comparisons between SARS-CoV-2 and SARS-CoV-1 transmission routes.

Against the claim that there may be high risk of airborne transmission, Ng et al. [21] reported from Singapore regarding 41 healthcare workers (HCWs) who were exposed to a SARS-Cov-2 positive patient during AGPs (including high risk AGP procedures such as noninvasive ventilation, emergency intubation and subsequent extubation) before the diagnosis was known. Eighty five percent of these workers wore only surgical masks and none of them developed COVID-19. Another study from Hong Kong reports 71 staff and 49 patients who were exposed in hospital to a patient with COVID-19 before diagnosis. In this case the patient had received 8L/min oxygen but no other AGPS. Contacts who developed respiratory symptoms or fevers were tested for SARS-CoV-2 (a total of 52 people tested) and none were positive [22] . As further evidence is presented we will have to reassess our understanding and review guidelines. At the present time no guidelines could be established based on specific evidence of infectivity of SARS-CoV-2 during AGPs. However, there is a high likelihood that SARS-CoV-2 transmission is similar to SARS and we must presume there is a significant risk of airborne transmission with AGPs until and unless new data demonstrate otherwise.

Evidence that individual procedures may increase risk of viral transmission has predominantly arisen from the SARS outbreak of 2002-3. During that time there were reports of airborne transmission of SARS [23] and investigation into viral transmission related to AGPs [24] [25] . Subsequent investigation involving influenza virus and MERS has also occurred [5] [26] . Data relating to potential AGPs are presented in Table I which describes the findings and the quality of evidence as it pertains to transmission of SARS-CoV-2. Despite these data and ongoing investigation there is still no consensus on which procedures constitute high-risk procedures for transmission of viral infections in general or in particular.

The WHO guideline on infection prevention and control of acute respiratory infections discusses the significant knowledge gap regarding AGPs and the lack of agreement as to which procedures should be included. They base their guidance on the widely referenced systematic review by Tran et al. [27] which identifies tracheal intubation as the only procedure which is consistently associated with SARS transmission. In accordance with this meta-analysis, the WHO state that NIV, tracheotomy and manual ventilation before intubation are associated with infection transmission in a few small studies and evidence was deemed to be very low quality by the reviewers. They state that no other procedures have been found to be significantly associated with infection transmission -investigated procedures were suction of body fluids, endotracheal aspiration and other intubation associated procedures, bronchoscopy, nebulised medication administration, use of HFNC, use of and manipulation of oxygen mask or bilevel positive airway pressure (BPAP) mask, defibrillation, chest compressions, insertion of nasogastric tube and collection of sputum.

The United States' Centers for Disease Control and Prevention provide a list of procedures that they report are often considered AGPs: open suctioning of airways, sputum induction, CPR, endotracheal intubation and extubation, NIV, bronchoscopy and manual ventilation. They state that it is uncertain whether nebuliser administration and high flow oxygen delivery produce infectious aerosols. The European Centre for Disease Prevention and Control guidance from March 2020 list tracheal intubation, bronchial suctioning and sputum induction as examples of AGPs and emphasise that nasopharyngeal swabbing should also be considered an AGP [9] .

Endotracheal intubation of SARS infected patients has been consistently associated with viral transmission to HCWs [28] . Eight observational studies investigated this and Tran et al. [27] analysed these and demonstrated an odds ratio of 6.6 (95% CI 2.3-18.9) from the four cohort studies and an odds ratio of 6.6 (95% CI 4.1-10.6) from the four case-control studies.

Current evidence shows an increased risk of transmission during resuscitation but it is difficult to separate the effects of individual procedures in the resuscitation process or to separate pre-intubation ventilation from intubation itself [24] [29] . Mechanical ventilation and CPR have been investigated in some studies where they have not been shown to be associated with SARS (or other acute respiratory infection) transmission [30] [31] . In the 2009 study by Liu et al. chest compressions were associated with infection risk but HCWs involved with chest compressions were more likely to be present at time of intubation and the authors found that these variables could not be distinguished from each other [29] .

Due to the lack of strong evidence against any infection risk, and due to likelihood of associated intubation with resuscitation, measures such as CPR, manual ventilation and tracheotomy are reasonably considered to be high-risk for infection transmission.

Bronchoscopy was not associated with infection transmission in the two studies published during the SARS outbreak. In one study 10 HCWs were exposed to bronchoscopy and none developed the infection [30] while in the other, two HCWs were exposed and one developed SARS [31] . Subsequent investigation based on Influenza A H1N1 suggested an increased detection of viral aerosols following bronchoscopy and airway suctioning [32] . Bacteria have been detected in ambient air following bronchoscopic procedures but risk to HCWs has not been studied further [33] .

Open suctioning of intubated patients' airways involves disconnecting the tracheal tube from the ventilator and this or the suction itself may lead to dispersal of aerosols from within the airway. Increased number of airborne particles near patients has been detected in association with airway suctioning but increased infection risk has not been demonstrated [34] .

There is considerable disagreement about the risk of aerosolisation and transmission of viruses due to NIV. Exhaled virus or aerosols have not been detected during its use and the evidence suggesting that NIV increases risk of acute respiratory infections is not strong [35] [36] . Hui et al. [37] in their widely referenced study demonstrate that air originating in a patient's airways can be spread within a radius ~1m around during NIV use. Subsequent studies show that while incorrect fitting of masks considerably increases the spread of exhaled air, in general there is not widespread dispersion of exhaled air [38] [39] . Furthermore there is little evidence of droplet or aerosol particles even within the 1m range [40] . There are no studies which show that air or aerosols distributed by NIV masks contain viral particles or fluid from the respiratory tract. NIV has not been clearly shown to increase risk of infection with SARS or other viral diseases however there are studies and case reports that describe an association [27] [41] . Raboud et al. [30] looked at 624 HCWs exposed to 45 confirmed SARS patients who were all intubated during the Toronto SARS outbreak in 2003. They found that 26 HCWs contracted SARS and 22 of these were attributed to a single patient. SARS developed in 38% of HCWs exposed to NIV as opposed to 17% of those who did not, which was a statistically significant association however this association was not upheld by Generalised Estimating Equation logistic regression or multivariate analysis. Of note, HCW presence during ECG recording was considered a stronger risk factor than during NIV -this suggests that variables other than aerosol generation played a considerable role in HCW risk.

Loeb et al. [31] and Yu et al. [42] both also reported an association between NIV and SARS transmission but found a stronger association related to oxygen masks. It is hypothesised that NIV may provide a protective benefit by limiting dispersal of droplets as patients cough [43] . While NIV failure rates are higher in de novo ARDS than in exacerbations of chronic disease, the prevention of a patient from requiring intubation may reduce risk of disease transmission. Cheung et al. [44] reported on 105 HCWs exposed to 20 

In the one review from the SARS outbreak which documented use of HFNC it was not shown to have an effect on risk of infection transmission. Manipulation of oxygen masks was significant in one of only two studies in which very small sample sizes were used and confidence intervals were large [30] [31] .

In simulated and experimental studies, HFNC and oxygen masks have been shown to disperse droplets and inhaled aerosols within radius up to 0.5 -0.6m. This is less than with NIV and continuous positive airway pressure (CPAP) masks, was noted to be flow rate dependent and was maximised by incorrectly fitting masks [38] [45] [46] . Loh et al. [47] recently demonstrated that use of HFNC may increase distance of droplet dispersal with coughing from an average of 2.48m to 2.91 in a study with 5 volunteers. Compared with conventional oxygen masks, HFNC use was not been associated with increased dispersal of bacterial particles in one study [48] . Specific studies with viruses have not been conducted. It remains unclear if HFNC should be considered an AGP based on its production or spread of droplets and there is insufficient evidence to confirm an associated infection risk.

Some association has been demonstrated between manipulation of oxygen masks and infection transmission, but neither were considered significant findings. Subsequent studies have not shown any association [27] [36] [49] .

Risk of transmission of SARS with nebuliser treatment received attention after a Hong Kong hospital reported widespread transmission of SARS after a patient had been treated with regular salbutamol nebulisers on the ward for 7 days [50] . Beyond the review by Tran et al. [27] there has been little subsequent research into the risk of transmission during nebuliser treatment. Tran et al. found two studies showing nebuliser use was associated with transmission of SARS, while one other did not. Their meta-analysis showed a wide confidence interval and no statistically significant effect. It is noted by Simonds et al. [39] that there is considerable dispersal of aerosolised particles from a nebuliser, but there is no research investigating whether particles originate in the patient or the nebuliser itself or whether viruses can be isolated from these particles.

Risk of contracting SARS after sputum induction was considered by one study with 42 HCWs involved with sputum collection. It was found that four of these HCWs developed SARS, which amounted to a small but not significant correlation [30] . Further research is clearly required to establish if there is any risk of airborne transmission, however the increased risk of droplet transmission related to coughing within close proximity is well understood and is likely to contribute to increased risk of infection if PPE is not adequate.

There is no evidence that endoscopy or trans-oesophageal echocardiography generate aerosols or convey an increased risk of transmission of viruses. It has only been shown that there is bacterial exposure to proceduralists during endoscopy procedures by culturing swabs taken from endoscopists' face shields after their procedures [51] . It has been suggested that endoscopic procedures for patients that are intermediate to high risk of being infected with SARS-CoV-2 should be treated with airborne precautions due to risk of viral transmission but there is no further evidence to support this [10] .

It has also been claimed that transoesophageal echocardiography (TOE) should be considered an AGP however there have been no specific studies on TOE to establish any increased risk of viral transmission. Driggen et al. [11] suggest that consideration for increased precautions should be given to procedures associated with increased risk of patient deterioration as resuscitation is associated with increased disease transmission. As discussed previously this may be reasonable but it should not be taken from this argument that TOE is an AGP or directly increases HCW infection risk.

There is almost no evidence pertaining directly to the infectivity of SARS-CoV-2 during aerosol generating procedures. Guidelines have been established mostly based on evidence related to SARS. Research on SARS and H1N1 Influenza A has established endotracheal intubation to be associated with infection transmission despite droplet infection precautions. Evidence does not confirm an association between other AGPs and infection risk when appropriate droplet PPE and precautions are used.

AGPs such as CPR, pre-intubation ventilation, tracheostomy and bronchoscopy do not currently have strong evidence to support an association with increased transmission but are generally considered high-risk procedures. These procedures are likely to increase transmission either directly or due to their close association with intubation. Other factors such as increased infectivity in more severe illness, and less stringent use of PPE in acute emergencies may also contribute. While other AGPs are often undertaken in emergencies bronchoscopy in general may be undertaken in a routine manner -given the possible increased risk of transmission and the lack of specific data on SARS-CoV-2, it is reasonable that bronchoscopy be avoided unless absolutely necessary.

Procedures such as NIV, HFNC and administration of medications by nebulisers have not been consistently associated with infection transmission. It is reasonable to limit any unnecessary usage but it is not clear that they should be withheld in patients who are likely to benefit from them. There is not enough evidence to suggest that any other procedures cause a risk of infection transmission and a definitive list of which procedures carry risk, and should be considered AGPs, has not be established. Further research is required to establish what transmission risk these procedures do carry and how clinicians can appropriately protect themselves. Guidelines should reflect the conclusions that can be made and the lack of evidence in other areas.

There are substantial gaps in evidence for the SARS-CoV-2 pandemic around transmission routes, HCWs risk, and safety of AGPs. Indeed there is a paucity of evidence with regard to infection risk associated with AGPs in general. These evidence gaps have not only produced a vacuum in knowledge of best practice, they have quickly fostered cultures of uncertainty amongst HCWs across many contexts. This has resulted in a range of consequences including likely increases in infective risks (through variation in practices and potential unnecessary depletion of finite resources) and lack of capacity to provide care when needed (due to fear of contagion).

In many respects, like other facets of the COVID-19 pandemic, the contagion is not only viral, but is behavioural. In this context, it is driven by unprecedented levels of professional uncertainty which offer the very real threat of widespread sub-optimal practices. As shown in other contexts, such as Ebola [59] [60], MERS [61] SARS [62] , the precarity that is experienced by HCWs in the midst of such an evidence vacuum produces, among other problems, highly localised practices (i.e. that are too stringent, or indeed, too lax), workplace absenteeism, and even withdrawal from providing treatment in frontline settings. In this sense, gathering best evidence around issues such as AGPs, which are currently being heavily debated within the context of COVID-19, provides a means of both mitigating uncertainty and acknowledging uncertainty as an important challenge for HCWs during this pandemic.

When considering the threats to HCWs it is also worth emphasising that the task ahead is not simply a matter of producing evidence across all relevant procedures which may offer risks of transmission, but promoting understanding of the impact of some level of uncertainty, and ensuring we are able to offset the potential for the parallel health service 'contagion' of anxiety around transmission risk through consistent messaging, consistent policies and practices, well-resourced PPE, and streamlined national and international guidelines.

Aerosol generating procedures are an important consideration for HCWs during the COVID-19 pandemic. There is not any evidence demonstrating an increased infection risk related to AGPs in SARS-CoV-2, but in related viruses a risk has been shown associated specifically with intubation of infected patients and it is possible that other AGPs convey a risk as well. There is a significant knowledge gap in this area and the risk HCWs face has not been established. Guidelines are necessary to ensure HCWs are aware of this fact and that their practice is consistent, appropriate and safe.

Healthcare worker risk may be increased further by clinical practice guidelines themselves which, written in the context of an evidence gap and of high professional anxiety, may cause wastage of protective equipment and resources, and prevent useful clinical interventions or otherwise influence individual patient treatment. We must mitigate uncertainty and anxiety not only by research to provide further evidence on which to guide practice, but by providing consistent and transparent guidelines and advice, and ensuring HCWs have appropriate PPE readily available. fourth study showed no infections in 105 HCWs exposed to NIV although they didn't assess risk in nonexposed workers. Air dispersal was detected to ~1m but no significant increase in aerosol production was shown. No significant effect on infection risk was seen (4 infected of 42 exposed).

Very low -Conclusions extrapolated from SARS -Very small study -Wide confidence interval -No evidence regarding nasopharyngeal swabbing [30] Endoscopy and transoesophageal echocardiography One prospective study investigating bacterial growth from facemasks used during endoscopies.

Significantly increased colony forming units detected post endoscopy compared to controls.

Very low -Conclusion extrapolated from study of bacteria -Indirect study with regard to aerosol transmission [51] 

World Health Organisation. WHO Director-General's opening remarks at the media briefing on COVID-19 -11

What we know so far: COVID-19 current clinical knowledge and research

COVID-19 may transmit through aerosol

Nosocomial Transmission of Emerging Viruses via Aerosol-Generating Medical Procedures

Infection prevention and control measures for acute respiratory infections in healthcare settings: an update

World Health Organisation. Rational use of personal protective equipment (PPE) for coronavirus disease

Staff safety during emergency airway management for COVID-19 in Hong Kong

Practical recommendations for critical care and anesthesiology teams caring for novel coronavirus (2019-nCoV) patients

European Centre for Disease Prevention and Control. Infection Prevention and Control for COVID-19 in Healthcare Settings n

COVID-19) outbreak: what the department of endoscopy should know

Cardiovascular Considerations for Patients, Health Care Workers, and Health Systems During the COVID-19 Pandemic

Infection prevention and control of epidemic-and pandemic-prone acute respiratory infections in health care n

Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19) in Healthcare Settings n

Unique epidemiological and clinical features of the emerging 2019 novel coronavirus pneumonia (COVID-19) implicate special control measures

Characteristics of and Important Lessons From the Coronavirus Disease 2019 (COVID-19) Outbreak in China

Integrated Surveillance of COVID-19 in Italy

World Health Organisation. Summary of probable SARS cases with onset of illness from 1

Exploring the reasons for healthcare workers infected with novel coronavirus disease 2019 (COVID-19) in China

Tracheal Intubation in Critically ill Patients with Noval Coronavirus Disease

Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1

COVID-19 and the Risk to Health Care Workers: A Case Report

Risk of nosocomial transmission of coronavirus disease 2019: an experience in a general ward setting in Hong Kong

Evidence of Airborne Transmission of the Severe Acute Respiratory Syndrome Virus

Possible SARS Coronavirus Transmission during Cardiopulmonary Resuscitation

Review of Aerosol Transmission of Influenza A Virus

Aerosol Generating Procedures and Risk of Transmission of Acute Respiratory Infections to Healthcare Workers: A Systematic Review

Airborne transmission and precautions: facts and myths

Risk factors for SARS infection among hospital healthcare workers in Beijing: a case control study

Risk Factors for SARS Transmission from Patients Requiring Intubation: A Multicentre Investigation in Toronto

SARS among Critical Care Nurses

Influenza Aerosols in UK Hospitals during the H1N1 (2009) Pandemic -The Risk of Aerosol Generation during Medical Procedures

Bacteria emitted in ambient air during bronchoscopy-a risk to health care workers?

Aerosol Distribution During Open Suctioning and Long-Term Surveillance of Air Quality in a Respiratory Care Center Within a Medical Center

Non-invasive respiratory support for patients with novel coronavirus pneumonia

Evaluation and Treatment Coronavirus (COVID-19)

Exhaled Air Dispersion Distances During Noninvasive Ventilation via Different Respironics Face Masks

Exhaled air dispersion during high-flow nasal cannula therapy versus CPAP via different masks

Evaluation of droplet dispersion during non-invasive ventilation, oxygen therapy, nebuliser treatment and chest physiotherapy in clinical practice: implications for management of pandemic influenza and other airborne infections

Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of

Noninvasive mechanical ventilation in high-risk pulmonary infections: a clinical review

Why Did Outbreaks of Severe Acute Respiratory Syndrome Occur in Some Hospital Wards but Not in Others?

Should noninvasive ventilation be considered a high-risk procedure during an epidemic?

Effectiveness of Noninvasive Positive Pressure Ventilation in the Treatment of Acute Respiratory Failure in Severe Acute Respiratory Syndrome

Exhaled air dispersion and removal is influenced by isolation room size and ventilation settings during oxygen delivery via nasal cannula

Assessment of the potential for pathogen dispersal during high-flow nasal therapy

The impact of high-flow nasal cannula (HFNC) on coughing distance: implications on its use during the novel coronavirus disease outbreak

Comparison of high-flow nasal cannula versus oxygen face mask for environmental bacterial contamination in critically ill pneumonia patients: a randomized controlled crossover trial

High-flow nasal therapy in adults with severe acute respiratory infection

A Major Outbreak of Severe Acute Respiratory Syndrome in Hong Kong

Risk of bacterial exposure to the endoscopist's face during endoscopy

Transmission of Severe Acute Respiratory Syndrome during Intubation and Mechanical Ventilation

Which preventive measures might protect health care workers from SARS?

Investigation of the influencing factors on severe acute respiratory syndrome among health care workers. Beijing Da Xue Xue Bao Yi Xue Ban

Factors associated with transmission of severe acute respiratory syndrome among health-care workers in Singapore

Illness in Intensive Care Staff after Brief Exposure to Severe Acute Respiratory Syndrome

A Case-Control Study on the Risk Factors of Severe Acute Respiratory Syndromes Among Health Care Workers

Cluster of SARS among Medical Students Exposed to Single Patient, Hong Kong

Fear, duty and the moralities of care: The Ebola 2014 threat

Ebola outbreak preparedness planning: a qualitative study of clinicians' experiences

Middle East respiratory syndrome coronavirus (MERS-CoV): what lessons can we learn

Fear and Stigma: The Epidemic within the SARS Outbreak

None declared