I’ve written this post in preparation for Wednesday’s IPS Journal Club (register here). The paper that I have chosen for the Journal Club is this one in the Journal of Infection Prevention, comparing the risk of SARS-CoV-2 dispersal through the air with an inhaler vs. nebuliser.

Why I chose this article:

• There has been a huge amount of debate about the transmission dynamics of SARS-CoV-2 through the air. (The latest suggestion from WHO on terminology around this topic is helpful.)
• The concept of “aerosol generating procedures” is disputed by some, but form part of national and international guidance on the management of respiratory viruses (e.g. CDC, WHO, English National IPC Manual).
• There has been a lot of debate as to whether delivering medicine via nebuilsation can generate infectious aerosols.

Design and methods:

• Study undertaken in Kansas City, USA.
• 11 patients were treated using both meter-dose inhaler or a breath-actuated nebuliser in a randomised crossover sequence.
• Air and surface samples were collected at baseline (i.e. before treatment), during treatment (air sampling), and after treatment (surface sampling).
• Aerosol sampling was undertaken using both cascade impactors and settle plates; surfaces were sampled using swabs.

Key findings:

• The amount of SARS-CoV-2 RNA detected from patients varied by study point (i.e. baseline, treatment 1, and treatment 2), with samples from three patients only containing detectable SARS-CoV-2 RNA in a single period.
• Overall, 4.3% (17/397) of total environmental samplings contained detectable SARS-CoV-2 RNA.
• Related to this, the amount of viral RNA detected was low in the positive samples, with a mean of 0.14 viral RNA copies/µL.
• There was no significant difference in environmental contamination in the baseline vs. inhaler vs. nebuliser period.
• There was no association between viral shedding and patient characteristics (i.e. patient viral load, vaccination status, coughing, length of hospital stay, supplemental oxygen usage) or environmental factors (i.e. temperature, humidity, number of room entries).

Strengths and limitations:

• This was a randomised controlled trial, including a cross-over to account for within-participant variation.
• Environmental samples included both air (by two different methods) and surfaces, with a high number of samples collected.
• Patients monitored for cough – although this showed no relationship between patient coughing and viral shedding, it was a nice addition to the protocol.
• Only 11 patients were included, which seems a bit low.  
• The primary endpoint (change in viral load from baseline) could not be analysed due to low frequency and level of SARS-CoV-2 RNA detection.
• There was quite a substantial difference in air change rate between the different rooms used (some had 4 and some had 12 air changes per hour).
• Around two thirds of the patients were treated with Remdesivir, which would have affected viral shedding.
• No viral culture was undertaken, and the detection of SARS-CoV-2 RNA is not the same as detecting viable SARS-CoV-2 virus.

Points for discussion:

• This was a strong study design, but how could it have been improved? It’s tempting to say by including more patients, but given the low level of SARS-CoV-2 RNA detection in the environment, this probably wouldn’t have helped.
• What does this add to our understanding of SARS-CoV-2 transmission through the air? SARS-CoV-2 RNA was detected from all but one sample location in the room, suggesting that there is widespread dispersal of SARS-CoV-2 RNA. This extended to the extract vents of the air handling system! However, both the frequency and the amount of SARS-CoV-2 RNA that was detected was low, and whilst viral culture was not performed, these low levels of SARS-CoV-2 are unlikely to be sufficient to initiate an infection in a recipient.
• Would these results hold true for all inhalers and nebulisers?

What this means for IPC:

• The findings from this study suggest that neither inhalers nor nebulisers are a risk of increasing the dispersal of SARS-CoV-2 through the air.  
• This implies that no additional precautions are required (over and above the usual PPE worn to care for a patient with SARS-CoV-2) when patients are being treated with nebulisers or inhalers.