Evidence Check - Epidemiology and transmission

Community transmission and hospital infection, stages of pandemic, immunity, vaccination.

Archive Surgical masks and oxygen therapy

Added: 19 Aug 2020

What is the evidence for wearing a surgical mask at the same time as an oxygen mask?
  • In vitro and clinical studies have demonstrated that placing a surgical mask on patients significantly reduces dispersion distance and levels of virus-infected bio-aerosol 20cm away from patients while coughing.
  • To mitigate the risk of spread of disease, a nasal cannula can be placed and covered with a surgical mask to limit the potential for environmental contamination.
  • Evidence on the percentage of supplemental oxygen that is delivered to the patient when wearing both a surgical mask and oxygen mask in the context of COVID-19 is lacking. A short report tested breathing air wearing a surgical mask on the face, second, breathing 6 l.min−1 oxygen via a Hudson mask placed over the top of a surgical mask and third, breathing 6 l.min−1 oxygen via a Hudson mask placed underneath a surgical mask, where the FIO2 measured was 0.20, 0.50 and 0.54, respectively.
  • Evidence on whether an oxygen mask can be worn over the top of a surgical mask, or underneath it includes: o A joint international consensus document recommends keeping a simple surgical face mask on patient, over nasal prongs and under any type of oxygen face mask. A short report calls for a surgical mask to be placed over the patient’s nose and mouth immediately following extubation, and for a Hudson mask to be placed on top due to the negligible difference in FIO2 when the Hudson mask is placed over a surgical mask. Chinese consensus guidelines also describe that the surgical or N95 mask is applied under the oxygen mask. While some consensus guidelines recommend placement of a surgical mask over patients being treated with high flow therapies.

Archive Face masks and COVID-19 transmission in the community

Added: 19 Jun 2020
Updated: 20 Jul 2020

What is the evidence that face masks help prevent the spread of COVID-19 in the community?
  • Context – transmission There is direct evidence of contact and droplet transmission of COVID-19. Flow physics and experimental models suggest, but have not demonstrated, airborne transmission. Epidemiological data on infection rates and transmission patterns are difficult to reconcile with long-range aerosol-based transmission. Where symptomatic patients are cared for, no studies to date have found viable virus in air samples.
  • Context – other jurisdictions Community mask use is either encouraged or mandatory in over 80 countries. Face coverings have been mandated in parts of Victoria. In countries with community transmission, the adoption of mandatory face mask use has been associated with decreasing infection rates. These decreases have not been directly attributed to face mask use, as a suite of measures is generally adopted.
  • Face mask evidence – non-COVID-19 Multiple systematic reviews examine the effect of face masks in community settings on reducing influenza like illness. Results are conflicting, with some reporting a protective effect and others no significant reduction in influenza like illness transmission. Respiratory etiquette, hand hygiene, social distancing, and isolation of cases, have a much stronger evidence base than face masks. Face masks are considered to be an additional measure, but there are concerns that masks can give a false sense of protection and may result in decreased compliance with other infection prevention practices.
  • Face mask evidence – COVID-19 There is very little evidence on use of face masks on public transport, however some reviews conclude masks may have a role in settings where social distancing is not feasible. Some experts counsel a precautionary approach despite a lack of clear evidence. Cloth masks have variable filtration depending on the fabric. A systematic review found no studies on mask use among COVID-19 negative people in community settings.

Archive Cardiac stress testing

Added: 16 Jul 2020
Updated: 17 Jul 2020

Is there evidence that cardiac stress testing is an aerosol generating procedure and what risk to healthcare workers does it carry?
  • Lists of aerosol generating procedures do not generally include cardiac stress testing. Some guides specify that cardiac stress testing is not an aerosol generating procedure, while another states that the risk is unknown
  • A nuclear cardiology service in Singapore identified exercise stress testing for myocardial perfusion imaging as a high-risk procedure for droplet production in the time of COVID-19. As such, treadmill exercise stress was discouraged over pharmacological stress, and medical and nursing staff who attended to suspect patients were required to don N95 masks with appropriate personal protective equipment (PPE)
  • During the COVID-19 pandemic, pharmacologic stress tests are preferred over exercise stress testing due to the risk of droplet production.
  • A consensus statement from various peak bodies in Australia and New Zealand, including the National Heart Foundation, note that certain cardiac investigations, including stress testing, pose significant viral transmission risk.
  • A statement from the American Society of Echocardiography states stress testing on patients with COVID-19 may lead to exposure due to deep breathing and/or coughing during exercise and that these tests should generally be deferred or converted to a pharmacological stress echocardiography. The British Society of Echocardiography notes a paucity of data with regard to the aerosol generating potential of exercise-based stress echocardiography, however the consensus opinion among UK experts is that it may be.
  • Infection control considerations for cardiac stress testing during COVID-19 include general infection control guidance as well as: patient screening, PPE, and room decontamination, including consideration of the turnaround time and percentage of airborne virus remaining in the room.

Archive COVID-19 transmission risk on aircraft

Added: 25 Jun 2020

There are few instances of confirmed transmission of COVID-19 on aircraft. 12 in Zhejiang, China, one possible instance in France.(1-3)
  • There are few instances of confirmed transmission of COVID-19 on aircraft. 12 in Zhejiang, China, one possible instance in France.(1-3)
  • Studies using computational fluid dynamics show a theoretical increased risk of transmission if seated in close proximity to an index case. Evidence from observational studies is inconclusive.(6)

Archive Hydrotherapy and COVID-19

Added: 17 Jun 2020
Updated: 18 Jun 2020

What evidence is available regarding the safe use of pools for hydrotherapy or aquatic physiotherapy during COVID-19?
Guidance regarding COVID-19 from physiotherapy societies, government and international bodies recommends:(1-5)
  • Current guidance from Centers for Disease Control and Prevention (CDC) notes there is no evidence to suggest that COVID-19 can be spread to humans through the use of recreational waters such as swimming pools.(1)

Archive Nosocomial COVID-19 infections

Added: 5 Jun 2020

Is there evidence of transmission of COVID-19 to and from healthcare professionals?
What strategies are available to reduce risk of nosocomial infections of COVID-19?
  • There are documented outbreaks of nosocomial spread of COVID-19, including infections in healthcare workers.
  • There are multiple reports of healthcare workers infected with COVID-19, as well as accounts of healthcare workers as a source of infection. However, the direction of transmission can be difficult to determine.
  • The Centre for Evidence Based Medicine reported on 15 April 2020 that 13.8% of COVID-19 positive cases in the UK were critical key workers in the National Health Service and other sectors. In China, more than 3,300 healthcare workers were infected (4% of the 81,285 reported infections), while in Spain on the 25 March nearly 6,500 medical personnel were infected, 13.6% of the country’s 47,600 total cases. As of 20 April 2020, there were 112 persons associated with the outbreak in north-west Tasmania, including 72 healthcare workers.
  • In Lombardy, over-referral led to significant numbers of unwell people presenting to hospital, with subsequent spread within the facility. Healthcare workers then had a higher risk of exposure and became vectors of onwards transmission.
  • Factors identified as contributing to nosocomial spread include: staff continuing to work despite showing symptoms, contact time, workplace activities, shortcomings in infection control practices, incomplete or delayed identification of close contacts of confirmed cases, high levels of staff mobility between different healthcare facilities, transfer of undiagnosed infectious or incubating patients between healthcare facilities.
  • Use of personal protective equipment (PPE), staff surveillance, infection prevention, control and monitoring, isolating suspected or confirmed COVID-19 cases, social distancing in hospitals, real-time monitoring of staff, setting up infection control teams, measuring body temperature or testing staff, roster changes and team grouping are strategies described to mitigate the risk of nosocomial infection in healthcare workers.
  • Modelling from the Imperial College COVID-19 response team found PCR screening of healthcare workers could reduce transmission of COVID-19 by a further 16-23%, on top of self-isolation based on symptoms, if results were available within 24 hours.
  • Healthcare workers are at different risk of infection based on factors such as setting, clinical role and their interactions with others.
  • There is a relationship between the stage of the pandemic and risk, e.g. in China most infections among healthcare workers occurred during the early stage of the outbreak, before protective measures were implemented.

Archive COVID-19 infectivity and transmission in children

Added: 4 Jun 2020

What is the evidence on the infection rate, infectivity and transmission of COVID-19 in children?
  • Publications have generally found a lower attack rate in children compared to adults.
  • Prevalence of COVID-19 infection is reported to be lower in children than in adults, however prevalence can be difficult to determine in children as most present with mild or no apparent symptoms.
  • There is preliminary evidence that children and young people have lower susceptibility to COVID-19, with a 56% lower odds of being an infected contact compared with adults.

Archive Sanitising and covering large medical imaging equipment

Added: 8 May 2020
Updated: 20 May 2020

Which method is most effective in sanitising large medical imaging equipment for COVID-19?
Which method is most effective in covering or protecting large medical imaging equipment for COVID-19?
Which method is most effective in sanitising linear accelerators and radiotherapy bunkers for COVID-19?
  • There is a variety of options for disinfectants to use on medical imaging equipment. Most guidelines suggest compliance with equipment vendor guidance to find the safest disinfectant for each piece of equipment.
  • Regulatory agencies (such as the Therapeutic Goods Agency) publish lists of approved disinfectants (Table 4).
  • Specific disinfectants for machines during COVID-19 have included: isopropyl alcohol 70%, diluted bleach solution (6mg chlorine releasing disinfectant tablet to 1,000ml water), 2,000mg/L chlorine-containing disinfectant
  • 500 to 1,000mg/L chlorine containing disinfectant
  • and alcohol-containing disposable disinfectant wipes.

Daily Evidence Digest

Rapid evidence checks are based on a simplified review method and may not be entirely exhaustive, but aim to provide a balanced assessment of what is already known about a specific problem or issue. This brief has not been peer-reviewed and should not be a substitute for individual clinical judgement, nor is it an endorsed position of NSW Health.

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