This review of the literature found singing within choirs is associated with an increased risk of transmission of COVID-19, but a combination of strategies will provide the best protection from COVID-19 transmission during choir rehearsals and performances. 

Major Findings: Five Point Summary

1: Singing is not free of risk.

Louder singing and speaking has been associated with increased emissions of airborne particles.

Our review of the literature found singing within choirs is associated with an increased risk of transmission of COVID-19, but a combination of strategies will provide the best protection from COVID-19 transmission during choir rehearsals and performances.  

2: Agreement on types of transmission

Although the routes of transmission in choir settings are not fully understood, there is agreement that the routes include direct person-to-person contact, and indirect transmission through droplets and aerosols and contact with object or surfaces (fomites). 

Our recommendations are divided into three categories—Ventilation (controlling airborne particles), Hygiene (contact with infected surfaces) and Physical Space (direct person-to-person contact)—however, there is not agreement on the relative  importance of each one. 

3: Multiple Control Measures likely to be the most effective

The scientific research surrounding singing and COVID-19 is emerging and fragmented, meaning there is not yet agreement on the risks of singing and the effectiveness of control measures. 

It has emerged from the review that until further primary research specific to choir settings has been undertaken, employing as many of the control measures as possible will increase the chances that they will be effective and provide choirs in communities with low COVID-19 prevalence with the best protection from COVID-19 transmission during choir rehearsals. 

In the overseas events reported, the common feature was the absence of a number of the control measures we now understand to be effective. 

4: Ventilation

Louder singing and speaking is associated with increased emission of aerosols and individual variability of airborne particle emission is high. We need to take aerosols seriously in a choral setting—think of them like the dissipation of incense or smoke that we can see. 

Recirculated air was noted in outbreaks overseas and effective ventilation is a plausible control measure for removing infected aerosols from a space. 

It is recommended that choirs work with their venues and ventilation specialists to better understand the effectiveness of ventilation systems and provide advice on airflow.

5: Wellbeing

Wellbeing is an important part of the health mix and ACN encourages choirs to take the wellbeing of their participants into account when developing a COVID-safe strategy and to reflect on the effects of not being able to sing with other people.

Before COVID-19, we could only speculate on what life would be like without choir, and knowing we had a once-in-a-lifetime window to fine out, ACN put a single survey question to the network during 2020— “Now that you’ve have time to reflect on what life is like without choir, what do you miss?”.

The results overwhelmingly revealed that being deprived of singing with other people made a significant impact on the psychological, physical and emotional wellbeing of our choral community. 

This single expression powerfully reflects the feeling of the greater network: “Singing fills me with joy and positivity. Without singing, I am much less. I miss the physical ‘workout’ of choir – it helps keep your brain and your body fit”.

An outbreak in a choir rehearsal in Spain ^[7] illustrates the problem well for choirs. On 11 September 2020, 41 members of the River Troupe Gospel attended a rehearsal leading up to their open-air performance two days later. The choir complied with risk mitigation measures at the rehearsal including temperature checks on arrival—hand washing, physical distancing, and masks. However, the venue’s windows were closed to avoid moths and mosquitoes and the air conditioning had been switched on because it was hot. One singer tested positive on the 13th September and all choir members and their close contacts isolated from that date. Thirty of the 41 singers developed COVID-19. 

Following are the questions that informed the literature review undertaken by Rosemary Byron-Scott and the major findings under each of those questions.

The literature review informed the recommendations we have included in this Guidance.  If you are keen to have a read, you can download it here. [860KB PDF] 

Aerosols and droplets are different sizes of airborne particles that behave differently in the air and may be infected with COVID-19. Droplets fall to the ground quickly and aerosols float like invisible smoke in the air.

Figure 1: Flow visualisation of aerosols and droplets emitted during sing ‘fa’.

COVID-19 can be spread in the following ways:

• Direct close contact with a person while they are infectious—usually face to face contact for at least 15 minutes; or being in the same closed space for at least 2 hours ^[5] 
• Large droplet spread through contact with droplets from an infected person’s cough or sneeze.
• Touching objects or surfaces (like doorknobs or tables, mobile phones, stair rails, elevator buttons) that have droplets from a cough or sneeze of an infected person, and then touching your mouth, nose, eyes or face2. 
• Breathing in infected aerosol—when an infected person talks, breathes, coughs or sneezes tiny particles containing infectious agents can remain suspended in the air for minutes to hours. 

So the risks of transmission and prevention strategies for choirs can be categorised into the following groups:

It has emerged from our review that implementation of multiple controls within a planned risk management strategy will provide the best protection from COVID-19 transmission during choir rehearsals. In simple terms, it has been recommended by many authors that employing as many of the control measures as possible, increases the chances that they will be effective—i.e. that a combination of strategies is more likely to be effective.

Choir rehearsals were reported to be associated with occurrences of the transmission of COVID-19 in other countries. The common feature was the absence of a number of the control measures we now understand to be effective. If choirs implement fewer control measures, meticulous records of attendance should be kept and choir management should be prepared to make quick contact with SA Health if a singer tests positive.

Figure 2 shows an adaption of Jones et al ^[4] risk schema to the choral setting. Further research is needed to quantify the independent effect of individual measures. However, it may serve as a visual reminder of the need to consider multiple control measures.

Figure 2: Risk of transmission of COVID-19 in choir rehearsals by control measure

The schema is qualitative and treats each control measure or risk as equal in quantity which is unlikely to be true. Masks are assumed to be surgical or non-medical rather than respirators. Other risks and controls that may be important are, for example rapid testing are not represented here.

Major finding

• Louder singing and speaking was associated with increased emission of aerosol and droplet sized particles
• Individual variability in the quantity of airborne particle emission is high. Some individuals are described as super-emitters because they can consistently emit a very large quantity of airborne particles.

Gaps in knowledge 

• Larger experimental studies of the quantities of aerosol and droplet emitted from singers/ groups of singers are needed. 
• Further research on the airborne particle emissions associated with different types of phonation used in singing is needed.

Implications

• Risk guidelines should include the risks associated with the volume of singing and, if appropriate, the use of amplification to avoid the need for loud singing.
• It is recommended that Lydia Morawska (QUT) be contacted regarding further information about mathematical modelling of choral rehearsals and performances, and evaluation of studies using mathematical models.

Major finding

• Both droplet and aerosol sized particles are big enough to carry the SARS-CoV-2 virus
• There is an agreed biological mechanism for emission of the SARS-CoV-2 virus in aerosol and droplet form from the lungs
• Theoretical modelling shows that exposure to the COVID-19 is possible within the timeframes of typical rehearsals if the environmental conditions encourage it
• Theoretical modelling suggests that increased room volume dilutes the concentration of virus

Gaps in knowledge 

• Further information about the minimum infectious dose for SARS-CoV-2 in choral settings 
• Further information about the detection of virions within aerosol in real-life settings is needed to establish its infectious potential

Implications

• Risk mitigation cannot rely solely on a directive to unwell people not to attend rehearsals.
• Effective ventilation of rehearsal venues is of critical importance
• Larger rehearsal rooms may reduce the exposure of singers to infected aerosols
• Rapid testing for active COVID-19, when available, may be useful to choirs to lower the risk of individuals, who don’t know they are unwell, attending rehearsals.

Major finding

• Virus transmission occurs through multiple routes including direct contact with people, and indirect contact with contaminated surfaces and aerosols.
• Shared food at rehearsals may be contaminated with virus either during preparation or shared consumption.
• Oral-faecal transmission of COVID-19 is possible.

Gaps in knowledge 

• The independent importance of each form of indirect transmission in choral settings has not been established 
• Further research on the infectivity of COVID-19 via fomites is needed. 

Implications

• Risk mitigation guidance should acknowledge direct and indirect transmission routes.
• Shared food should not be consumed at singing gatherings.
• Cleaning protocols should include toilets.

Major finding

• It should be assumed, due to observations of the outbreaks, that choral singing does pose a risk of infection with COVID-19. 
• Populations at risk of more severe outcomes after infection with COVID-19 included older age groups and people with co-morbid conditions.
• Transmission can occur through contact with people who have asymptomatic or pre-symptomatic disease.
• Settings with higher risk of one-to-many transmission (super-spreading) included those with large groups of singers in poorly ventilated rehearsal venues.

Gaps in knowledge 

• Further research is needed on the degree of additional risk due to choral singing in comparison with a gathering in the same space of the same size where there was extended loud non-singing vocalisation.
• Evaluation of the role of rapid testing for COVID-19 positive status in choristers is needed.

Implications

• Risk mitigation for choirs should be planned and diligently implemented.
• Risk mitigation cannot rely solely on advice to symptomatic singers to stay home.
• Risk mitigation cannot rely solely on the number of reported positive cases in the community
• Risk mitigation for large choirs should include control measures to limit the number of singers at a rehearsal where possible through, for example, increasing the use of sectional rehearsing
• Risk mitigation should include control measures that maximise the effective ventilation of rehearsal spaces
• Choirs should be alert to the probable increased risks of COVID-19 in autumn 2021 in South Australia

Major finding

• Effective ventilation has been shown to be a plausible and probably important control measure for removing infected aerosols from a space
• Ineffective ventilation was implicated in outbreaks in choral rehearsals
• Outdoor spaces provide effective ventilation due to maximum dilution of infected aerosol 
• The air changes per hour (ac/h) were a useful indicator of effective ventilation 
• Fresh air input to ventilation systems was important in the dilution of aerosols
• Effective ventilation, whether natural or mechanical comprised airflow directed away from singers to an external outlet
• Filtration systems that decontaminate air can be incorporated into ventilation systems

Gaps in knowledge 

• Further research on portable air cleaners suited to choirs is needed
• Studies of the effectiveness of ventilation in churches and other large venue spaces would benefit choirs

Implications

• Ventilation of rehearsal rooms is a crucial control measure for choirs 
• Choir management should understand the effectiveness of ventilation systems in rehearsal venues including during heating and air conditioning modes
• If relying on open windows and doors to ventilate a rehearsal venue, choir management should aim for fresh air to flow in a direction past individual singers directly to the outlet

Major finding

• Effective cleaning protocols are an important component of a risk mitigation strategy
• Training of staff combined with testing of cleaned environments and effective disinfectant products were important factors in successful cleaning protocols

Gaps in knowledge 

• All aspects of the evaluation of cleaning protocols merit further research

Implications

• Choir management should have an understanding of the cleaning protocols of venues used for rehearsals and performances
• Choirs should ensure a process for the cleaning of venues before and after rehearsals and performances is undertaken

Major finding

• Physical distancing of at least 2m to the front and 1.5m to the side is likely to be an effective control measure for choirs to prevent transmission through droplets emissions.
• Physical distancing is not likely to be effective in controlling aerosol transmission of COVID-19.

Gaps in knowledge 

• Further research to support physical distances of 2m to the front and 1.5m to the side for choral singing is needed.

Implications

• Physical distancing is an important control measure for choirs within an integrated risk mitigation strategy.
• Conductors should be located at least 2m away from singers 

Major finding

• Masks may provide added protection to singers when used in conjunction with physical distancing, hygiene, and ventilation control measures

Gaps in knowledge 

• Further evaluation of the benefit of masks as a preventative control measure for choirs in the context of low community prevalence of COVID-19 is needed

Implications

• If community transmission of COVID-19 was to increase in South Australia, masks worn by the majority of the choir may be an important control measure
• Masks for congregational singing and other equivalent situations may be a strategy for allowing participation in singing if used in conjunction with physical distancing, hygiene and ventilation control measures.
• Choir management should have an understanding of the effective use of masks. Singers should experiment with singing in masks.

Major finding

The use of multiple control measures within a planned risk management strategy will provide the best protection from COVID-19 transmission during choir rehearsals.

The precautionary principle would suggest implementing as many control measures as possible, prioritising effective ventilation, hand hygiene, environmental cleaning and physical distancing.

Gaps in knowledge

Scientific evaluation of combinations of multiple control measures that would best protect people in the choral singing context

Implications

If choirs implement fewer control measures, meticulous records of attendance should be kept and choir management should be prepared to make quick contact with SA Health if a singer tests positive.