Minnesota Extension Advice: Do Not Exhibit Lactating Dairy Cows at Public Events Through 2024

Credit CDC 

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While the spread of HPAI H5 to humans has thus far been restricted (at least in the United States) to agricultural workers, in other parts of the world just strolling through or living near a live bird market has been linked to increased risk of infection (see Open Forum Inf. Dis.: High Prevalence of HPAI Virus In Vietnam's Live Bird Markets).

The standard advice from WHO in countries where HPAI H5 is circulating remains: 

`The public should avoid high-risk environments, such as live animal markets or farms, and avoid contact with live poultry or surfaces that might be contaminated by birds or poultry droppings . . . '.

Similar advice is offered to citizens of Hong Kong who may be traveling to China, where H5N6, H5N1, and several other avian viruses can be found:

Travellers to the Mainland or other affected areas must avoid visiting wet markets, live poultry markets or farms.

This advice is borne of two decades of experience dealing with HPAI.  While the exact route of infection isn't always determined, we've seen studies showing the ambient air at live bird markets can carry detectable virus particles. 

• In 2015 (see CIDRAP: H5N2 Roundup & Detection In Environmental Air Samples) we looked at air sampling conducted by the University of Minnesota around infected poultry farms that found evidence of airborne virus particles.
• A similar study (see J. Infection: Aerosolized H5N6 At A Chinese LBM (Live Bird Market) in 2016.
• And in 2019 we saw a study which suggested  Nature: Airborne Transmission May Have Played A Role In Spread Of U.S. 2015 HPAI Epizootic.

We've even seen evidence that insect vectors, like the common house fly (see Kyushu University: The Return Of The Fly), can become a mechanical transmitter of H5N1 influenza virus.  

The risks from infected livestock (poultry, cows, goats, etc.) - even here in the United States - is a genuine concern.  So much so, that the CDC is currently recommending that farm workers wear PPEs.

CDC PPE recommendations for Farm Workers

Over the past 3 weeks at least 10 farm workers (across 3 American farms) have been infected with HPAI H5N1.  I say `at least' because there are anecdotal reports of symptomatic workers who have refused testing, and because there may be others in the queue. 

Against this backdrop there is a vigorous debate over the risks of allowing agricultural exhibits at state and county fairs, which really kick off in middle America during August & September. 

These range from small local venues to state fairs which attract more than a million visitors. Altogether, it is a multi-billion dollar industry, and these prize animals represent the hard work and dedication of tens of thousands of exhibitors, many of whom are still in school. 

And understandably, nobody wants to be the Grinch who stole the county fair.  

As a result, we've seen a wide range of bio-safety rules promulgated by state and local authorities. Some, like from Michigan and Wisconsin, have been fairly strict.  Others, have been less rigorous, although I would note that yesterday Texas ordered Pre-Movement Testing for Exhibition Dairy Cattle.

We've previously seen the spread of swine-variant influenza viruses to the public through these types of exhibitions (see EID Journal: Shortening Duration of Swine Exhibitions to Reduce Risk for Zoonotic Transmission of Influenza A Virus).  

The CDC has long advised those who are at higher risk of serious flu complications (including children under 5, adults over 65, pregnant women, and those with certain chronic medical conditions), to avoid pigs and the swine barn altogether.

With a new, and potentially more dangerous, HPAI H5 virus now spreading in American livestock, the question becomes, how much risk is acceptable?  And how much faith can we put in the existing (and often inconsistent) biosecurity requirements? 

The risk is more than just to humans, since fairs often bring together poultry, cattle, goats, and pigs.  This `mixed species' environment provides opportunities for the spillover, and spread, of viruses - and potentially - a myriad of reassortment possibilities. 

All of which brings us to a guidance document, issued by the University of Minnesota Extension Office, which calls of the banning of lactating cattle (regardless of testing) from agricultural exhibits until 2025 (and possibility beyond). 

While this would be a bitter pill for many if adopted, the authors warn : `The risk of exposure to H5 influenza for both animals and humans at fairs and exhibitions is high'.

The full report goes into their rationale, and is well worth reading in its entirety.   I'll have a postscript when you return.  

Extension advice: Do not exhibit lactating dairy cows at public events through 2024
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Extension advice: Do not exhibit lactating dairy cows at public events through 2024

July 24, 2024

This article has specific recommendations for animal exhibitions in 2024 in Minnesota due to the outbreak of H5N1 in dairy and poultry operations across the state and country. It also contains information about the spread of influenza A viruses relevant to the general public and people involved in farm animal operations.

Given the high risk posed by lactating dairy cattle to other cattle, the rest of the exhibition community, and the public, lactating dairy cattle should not attend exhibitions including county and state fairs, until 2025 or beyond.

          (Continue . . . )

Short of HPAI H5 suddenly transmitting efficiently in humans, the `next-worse-case' scenario would be for the virus to begin spreading in pigs.  There, it could find a plethora of better-adapted swine flu viruses with which to reassort, substantially increasing the risk of a pandemic. 

While unfortunate for the exhibitors, given the stakes, I find it hard to argue with the advice to exclude lactating cattle from state and county fairs.  Whether these recommendations will be adopted widely, remains to be seen. 

There are, of course, other ways H5N1 might succeed in sparking a pandemic. But given what we know about HPAI, it makes little sense to make it any easier for the virus. 

UKHSA Raises Risk Assessment On HPAI H5N1 In Humans

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Six months can be a long time when discussing the rapidly changing threats from emerging infectious diseases.  Last January the UK's Health Security Agency released a risk assessment that reassuringly placed the HPAI H5N1 virus in a pre-pandemic level 3 category. 

They wrote:

Assessment

The avian influenza outbreak in the UK is assessed as at risk level 3*. The apparent transmission between mink is of significant concern but there is no clear evidence that this has continued in mammalian species since the initial outbreak. The UK assessment is consistent with the international picture with the same or similar viruses detected in multiple regions, evidence of mammalian spillover, but very few detected human infections.

At present, there are no indicators of increasing risk to human health, however this is a low confidence assessment. The risk assessment is dynamic and requires regular review during this period of unusually high levels of transmission in birds with mammalian spillover.

Two months later we learned of the outbreak of HPAI in American cattle - and of its rapid spread across the nation - which led to a revised risk assessment from the UKHSA in May, where they stated: 

Situational assessment: the outbreak is currently at level 3 (with high confidence) and may have risen to level 4 (low confidence)

Over the past 3 weeks we've seen a 4th H5 human infection linked to dairy cattle exposure, and 9 more linked to infected poultry. Considering that up until 3 months ago, the U.S. had only reported 1 (weakly positive) case, that represents a significant increase. 

We've also seen recent reports suggesting `sustained and efficient' transmission of the virus - a highly specific phrase which is not used lightly - both in cattle, and to a lesser degree in marine mammals. 

Yesterday the UKHSA released an updated risk assessment which raises - incrementally - their risk assessment from level 3 to level 4 (moderate confidence). The full report (including their rationale) runs 11-pages, so I've only posted some excerpts below.  

Follow the link to read the full assessment.  I'll have a brief postscript after the break. 

Influenza A(H5N1) 2.3.4.4b B3.13: UScattle outbreak update 

Human health evidence review and situational assessment 17 July 

UKHSA, APHA, FSA, and Defra

Overview

The UK Health Security Agency (UKHSA) is working with the Animal and Plant Health Agency (APHA), the Department for Environment, Food and Rural Affairs (Defra), Food Standards Agency (FSA), and the public health agencies of the 4 nations to monitor the risk to human health from emerging influenza viruses.

A previous assessment of this situation was published in May 2024.

Current evidence review

1. Animal outbreak

There is ongoing transmission of influenza A(H5N1) in the US, primarily through dairy cattle but with multispecies involvement including poultry, wild birds, other mammals (cats, rodents, wild mammals) and humans (1, 2). There is high uncertainty regarding the trajectory of the outbreak and there is no apparent reduction in transmission in response to the biosecurity measures that have been introduced to date. There is ongoing debate about whether the current outbreak should be described as sustained transmission given that transmission is likely to be facilitated by animal farming activities (3). However, given that this is a permanent context, the majority of the group considered this outbreak as sustained transmission with the associated risks.

The available genomic data show a single expanding clade, genotype B3.13, consistent with ongoing transmission through dairy cattle and spillover into other mammals and birds.

2. Human cases

There is evidence of zoonotic transmission (human cases acquired from animals). There is likely to be under-ascertainment of mild zoonotic cases (4). There have been ten human cases detected associated with the current US outbreak, 4 in dairy workers at separate farms and 6 in poultry workers exposed during a single depopulation event at which a large number of workers were symptomatic (1).

 

Environmental factors may have contributed to increased viral exposure at this site (5). Human case genomes where available are within the cattle outbreak clade although the first human case in Texas is distinct (3). The sequence from this case (EPI_ISL_19027114) does contain the HA L131Q and T211I mutations present in all B3.13 sequences, but not contain the PB2 M631L, PA K497R or the NA N71S mutations observed in the main cattle outbreak clade. It contains PB2 E627K and D441N mutations, K142E in PA, and S7L and Q40R in NS1 that are not observed in other B3.13 sequences.

The ongoing cattle outbreak in dairy cattle with spillover to poultry farms means that there could be large numbers of human exposures and increased opportunity for zoonotic cases. However, there are insufficient data to assess whether the rate of zoonotic infection is unusually high.

(SNIP)

4. Evidence relevant to human transmissibility

Despite the increased activity of the bovine virus polymerase with the PB2 M631L and PA K497R mutations in human and other mammalian cells, the lack of human receptor binding supports the virological observations that bovine virus (EPI_ISL_19014384), like earlier clade 2.3.4.4b viruses that circulated in the UK, replicates and spreads poorly in human airway epithelium at 33°C (similar to temperatures in human nasal passage) (10). Preprint data finds respiratory inoculation is possible in experimentally infected heifers and published data suggests inefficient respiratory transmission in the ferret model (8, 16, 17).

5. Characteristics of genotype B3.13

There are insufficient data to assess whether the genotype B3.13 was already fitter in birds or mammals at the point of spillover (that is, had a predisposition to cause a mammalian outbreak) and therefore it is difficult to assess whether other genotypes seen in Europe could cause similar outbreaks given similar opportunity. In vitro data shows that other influenza A viruses with internal genes derived from avian viruses including those of clade 2.3.4.4b replicate efficiently in bovine cells (10). Widespread transmission in marine mammals is also noted in South America, involving a slightly different genotype (18).

With the current evidence we should not assume that the risk of a mammalian outbreak is limited to clade B.3.13.

6. Risk of reassortment

There is an ongoing elevated risk of reassortment with other influenza viruses given the range of animal and human infections occurring. There is also early in vitro data suggesting that human seasonal influenza viruses can replicate in bovine cells (10). This implies that reassortment resulting in exchange of genes between the bovine virus, avian influenza viruses and fully human adapted influenza viruses could also occur in cattle, as it does in pigs.

Current situational assessment

Levels are indicators that a zoonotic influenza virus outbreak may be an increasing human health threat, either because the opportunities for it to evolve are increasing or because there is evidence that it has already begun to evolve. All levels are pre-pandemic events. The current situational assessment is shown in Table 1 alongside accompanying evidence, updated from the previously published situational assessment (May 2024).

            (Continue . . . )


Risk assessments are - by necessity - based on older, often fragmented, and usually rapidly changing information.  As such, they are always going to be behind the curve.  

They can be useful, however, since they can show changes in our levels of concern over time. And it is clear that concerns over HPAI H5 are rising around the globe. 

In addition to raising the pre-pandemic level, this report also acknowledges that it isn't just the bovine B3.13 genotype - currently spreading in North America - that poses a zoonotic threat.  This is a palpable shift from the UK HAIRS Risk Statement On Avian Influenza (H5N1) In Livestock released in late May.

Zoonotic threats advance and retreat, often without warning, and so we could find ourselves back at level three in the fall, still at level four, or somewhere decidedly worse.   

While these risk assessments can't predict the future, they can help us decide where best to put our prevention and preparedness efforts. 

Assuming, of course, that those who are in charge of such things are actually paying attention. 

CDC Statement On Three Confirmed H5N1 Infections At Colorado Poultry Farm

Recommended PPE For Farmers 

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In a follow-up to the announcement earlier this afternoon from the Colorado Health Department, we have the following statement from the CDC on the three latest confirmed H5N1 cases among poultry workers. 

CDC Confirms Three Human Cases of H5 Bird Flu Among Colorado Poultry Workers

STATEMENT

Media Statement - Three additional human cases of highly pathogenic avian influenza (HPAI) A(H5) (“H5 bird flu”) virus infection have been confirmed by the Centers for Disease Control and Prevention (CDC) in association with a second poultry farm in Northeast Colorado/Weld County.

For immediate release: July 25, 2024

CDC Media Relations

(404) 639-3286

http://www.cdc.gov/media

July 25, 2024 – Three additional human cases of highly pathogenic avian influenza (HPAI) A(H5) (“H5 bird flu”) virus infection have been confirmed by the Centers for Disease Control and Prevention (CDC) in association with a second poultry farm in Northeast Colorado/Weld County. Colorado previously announced one of them as a presumptive positive case on Saturday, July 20. The three confirmed cases occurred in people who were working directly with infected poultry at a commercial egg layer operation that had reported an outbreak of H5 bird flu among poultry.

All three people have mild illness and have been offered the antiviral drug, oseltamivir, for treatment. State and local officials continue to monitor poultry workers on farms with infected poultry. This is a different farm in Colorado from the one where on Friday, July 19, CDC confirmed two additional human cases of H5 bird flu, which brought the total human cases associated with that first poultry farm to six. With the addition of these three new confirmed human cases, the total number of human cases associated with the current poultry outbreaks in Colorado is nine. A CDC multidisciplinary, bilingual field team is currently deployed to support Colorado’s response to ongoing poultry outbreaks of H5 bird flu in the state.

Confirmation of these three additional cases brings the total number of human cases of H5 bird flu reported in the United States since April 2024 to 13. Prior to 2024, the only previous human case of H5N1 bird flu in the United States was reported among a poultry worker in Colorado in April 2022. Counting that case, there have been 14 total human cases of H5 bird flu in the United States since 2022.

Based on available data, CDC’s current assessment is that the risk to the general public from H5N1 remains low. As we learn more, we will continue to assess the situation and provide updates. These preliminary results again underscore the risk of exposure to infected animals. There are no signs of unexpected increases in flu activity otherwise in Colorado, or in other states affected by H5 bird flu outbreaks in cows and poultry. Human infections with this novel influenza A virus (and others) are concerning because of the potential to cause severe, widespread disease. To date, we have not seen genetic changes in the virus that would make it more likely to transmit between humans, but we are closely monitoring it.

CDC’s recommendations related to H5 virus have not changed at this time. Findings from the investigation will inform whether guidance changes are needed. The investigation will include looking into compliance with the recommended use of personal protective equipment. Historically, most human cases of bird flu infection have happened in people who are not wearing recommended personal protective equipment. An analysis of the virus sequences from this outbreak also will be important to determine if a change in the risk assessment is warranted.

CDC Recommendations

• People should avoid unprotected exposures to sick or dead animals, including wild birds, poultry, other domesticated birds, and other wild or domesticated animals (including cows).

• People should also avoid unprotected exposures to animal feces (poop), bedding (litter), unpasteurized (“raw”) milk, or materials that have been touched by, or close to, birds or other animals with suspected or confirmed A(H5N1) virus.

• CDC has interim recommendations for prevention, monitoring, and public health investigations of A(H5N1) virus infections in people. CDC also has updated recommendations for worker protection and use of personal protective equipment (PPE). Following these recommendations is central to reducing a person’s risk and containing the overall public health risk.

Colorado: 3 Confirmed Human H5 Infections at 2nd Poultry Farm

https://www.cdc.gov/flu/pdf/avianflu/avian-flu-transmission.pdf

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Today Colorado's Health Department announced 3 confirmed cases of HPAI H5 among poultry workers on the 2nd farm (one case was reported as presumed positive on Monday), bringing to 10 the number of cases (1 cattle linked, 9 poultry linked) reported by that state over the past few months. 

No details are provided on these 2 new cases, with the thrust of the announcement focused more on the unveiling - later today - of a new data table for tracking cases.  We should get more details tomorrow, however, from the CDC weekly roundup. 

The brief statement follows.

State health officials to publish data table for human cases of avian flu in Colorado

Coloradans can find twice weekly updates on avian flu in humans on the CDPHE website

Denver (July 25, 2024) — The Colorado Department of Public Health and Environment — in coordination with the Colorado Department of Agriculture and State Emergency Operations Center — is reporting three confirmed cases of avian flu in humans at a second farm in Weld County, bringing the total number of cases to three at that particular farm. Public health officials first reported news of the virus at a second farm last Saturday. This update brings Colorado's total number of confirmed avian flu cases in humans to 10 — nine cases at two poultry farms and one case from a dairy farm.

Later today, the Colorado Department of Public Health and Environment will launch a data table to track cases of avian flu in humans. The table will be updated on the CDPHE website by 4 p.m. every Tuesday and Thursday.

The biweekly update will include the number of presumptive positive human cases, number of confirmed human cases, approximate number of people tested, and a link to the Colorado Department of Agriculture for the number of impacted dairy and poultry farms.

The Colorado Department of Agriculture provides data on avian flu in poultry and dairy cattle, which is updated weekly or as data is confirmed.

The CDC continues to state that the risk of avian flu to the general public is low. So far, we have not seen evidence of person-to-person transmission. Epidemiologists both here in Colorado and at CDC are monitoring for genetic variations in the virus and changes in transmission patterns.

It seems likely that more cases will turn up in the days and weeks ahead.

Stay tuned. 

HK CHP Monitoring Another Fatal H5N6 Infection (Anhui, China)

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It's been more than 3 years since Anhui province has reported an H5N6 case (link), but today Hong Kong's CHP is reporting on a fatal case (70, F) who fell ill following a visit to a live poultry market in the middle of June and died on July 8th. 

While getting reliable, and timely, reports out of China can be a challenge, this is only the 3rd case reported on the Mainland this year.  The other two cases were from Fujian Province, and all three have proved fatal. 

It is certainly possible that there are cases that are either not being detected by local surveillance, or are simply not reported.  The ECDC chart below shows we are a far cry from where we were in 2021 (n=35 cases). 

But these reports - along with Cambodia's recent surge in clade 2.3.2.1c H5N1 virus infections - remind us that HPAI H5 continues to explore multiple evolutionary paths, and that we may see others emerge over time.

CHP closely monitors human case of avian influenza A(H5N6) on Mainland
 
The Centre for Health Protection (CHP) of the Department of Health is today (July 25) closely monitoring a human case of avian influenza A(H5N6) on the Mainland, and again urged the public to maintain strict personal, food and environmental hygiene both locally and during travel.

The case involves a 70-year-old female living in Hefei in Anhui Province, who had visited a live poultry market before the onset of symptoms. She developed symptoms on June 17 and was admitted to a hospital for treatment on June 19. She passed away on July 8.

From 2014 to date, 92 human cases of avian influenza A(H5N6) have been reported by Mainland health authorities.

"All novel influenza A infections, including H5N6, are notifiable infectious diseases in Hong Kong," a spokesman for the CHP said.

Travellers to the Mainland or other affected areas must avoid visiting wet markets, live poultry markets or farms. They should be alert to the presence of backyard poultry when visiting relatives and friends. They should also avoid purchasing live or freshly slaughtered poultry, and avoid touching poultry/birds or their droppings. They should strictly observe personal and hand hygiene when visiting any place with live poultry.

Travellers returning from affected areas should consult a doctor promptly if symptoms develop, and inform the doctor of their travel history for prompt diagnosis and treatment of potential diseases. It is essential to tell the doctor if they have seen any live poultry during travel, which may imply possible exposure to contaminated environments. This will enable the doctor to assess the possibility of avian influenza and arrange necessary investigations and appropriate treatment in a timely manner.

While local surveillance, prevention and control measures are in place, the CHP will remain vigilant and work closely with the World Health Organization and relevant health authorities to monitor the latest developments.

The public should maintain strict personal, hand, food and environmental hygiene and pay attention to the following issues to prevent avian influenza:

• Avoid touching poultry, birds, animals or their excrement, or contaminated environment;
• When buying live chickens, do not touch them and their droppings. Do not blow at their bottoms. Wash eggs with detergent if soiled with faecal matter and cook and consume the eggs immediately. Always wash hands thoroughly with soap and water after handling chickens and eggs;
• Eggs should be cooked well until the white and yolk become firm. Do not eat raw eggs or dip cooked food into any sauce with raw eggs. Poultry should be cooked thoroughly. If there is pinkish juice running from the cooked poultry or the middle part of its bone is still red, the poultry should be cooked again until fully done;
• Wash hands frequently, especially before touching the mouth, nose or eyes, before handling food or eating, and after going to the toilet, touching public installations or equipment such as escalator handrails, elevator control panels or door knobs, or when hands are dirtied by respiratory secretions after coughing or sneezing; and
• Wear a mask if fever or respiratory symptoms develop, when going to a hospital or clinic, or while taking care of patients with fever or respiratory symptoms.

​The public may visit the CHP's pages for more information: the avian influenza page, the weekly Avian Influenza Report, global statistics and affected areas of avian influenza, the Facebook Page and the YouTube Channel.

Ends/Thursday, July 25, 2024

Recent studies (see mSphere: An HPAI H5N6 Virus With Remarkable Tropism for Extra-respiratory Organs in the Ferret Model) suggest the H5N6 virus continues to adapt to mammalian hosts, while 2 years ago the Lancet published Resurgence of H5N6 Avian Influenza Virus in 2021 Poses New Threat to Public Health.

All of which makes the lack of information coming out of China less than reassuring. 

BMJ: Personal Protective Effect of Wearing Surgical Face Masks in Public Spaces

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Although we've seen ample evidence that the consistent wearing of surgical masks and/or N95 respirators in high risk areas (crowds, poorly ventilated indoor spaces, etc.) can significantly reduce the risk of respiratory infection, there remains a high level of resistance to donning them. 

I live in what would be described as a `retirement' community, but I rarely see anyone wearing a mask in public (unless I'm looking in a mirror). 

Masks are admittedly inconvenient, and can be uncomfortable (particularly in the summer), but at my age (> 70) I consider wearing them far less onerous than a week in bed with COVID, or worse, being hospitalized.  

Others may look at their individual risks, and come to a different conclusion. 

Unfortunately, the internet is filled with memes declaring that `Masks don't work', erroneously citing a 2023 Cochrane study in order to prove their point. 

In March of last year Karla Soares-Weiser, Editor-in-Chief of the Cochrane Library, issued a statement (see Cochrane Statement On Misinterpretations Of Their Mask Study) clarifying the study's findings.  

But memes are no slave to facts, and so people continue to post (and believe) them.

With COVID rising once again and the fall respiratory season not far off, people will once again need to evaluate the risks and rewards of wearing a mask in public. 

Today we've a new clinical trial that finds that wearing even a surgical mask in public can reduce the risks of respiratory infection.  While the impact was modest (a 29% reduction in symptomatic infections), it is a relatively simple and low-cost intervention. 

I've reproduced the abstract and summary below, but you'll want to follow the link to read the report (and its limitations) in its entirety.  I'll have a postscript after the break. 

CCBYNC Open access

Research
Personal protective effect of wearing surgical face masks in public spaces on self-reported respiratory symptoms in adults: pragmatic randomised superiority trial

BMJ 2024; 386 doi: https://doi.org/10.1136/bmj-2023-078918 (Published 24 July 2024)
Cite this as: BMJ 2024;386:e078918
Article
Related content
Metrics
Responses
Peer review

Runar Barstad Solberg, scientist1,Atle Fretheim, professor and research director12, Ingeborg Hess Elgersma, scientist1, Mette Fagernes, senior adviser3, Bjørn Gunnar Iversen, senior medical officer3, Lars G Hemkens, senior scientist456, Christopher James Rose, statistician17, Petter Elstrøm, senior scientist1Author affiliations
Correspondence to: R B Solberg runar.solberg@fhi.no (or @Runar_Solberg on X)Accepted 29 May 2024

Abstract

Objective To evaluate the personal protective effects of wearing versus not wearing surgical face masks in public spaces on self-reported respiratory symptoms over a 14 day period.

Design Pragmatic randomised superiority trial.

Setting Norway.

Participants 4647 adults aged ≥18 years: 2371 were assigned to the intervention arm and 2276 to the control arm.

Interventions Participants in the intervention arm were assigned to wear a surgical face mask in public spaces (eg, shopping centres, streets, public transport) over a 14 day period (mask wearing at home or work was not mentioned). Participants in the control arm were assigned to not wear a surgical face mask in public places.

Main outcome measures The primary outcome was self-reported respiratory symptoms consistent with a respiratory infection. Secondary outcomes included self-reported and registered covid-19 infection.

Results Between 10 February 2023 and 27 April 2023, 4647 participants were randomised of whom 4575 (2788 women (60.9%); mean age 51.0 (standard deviation 15.0) years) were included in the intention-to-treat analysis: 2313 (50.6%) in the intervention arm and 2262 (49.4%) in the control arm. 163 events (8.9%) of self-reported symptoms consistent with respiratory infection were reported in the intervention arm and 239 (12.2%) in the control arm.

The marginal odds ratio was 0.71 (95% confidence interval (CI) 0.58 to 0.87; P=0.001) favouring the face mask intervention. The absolute risk difference was −3.2% (95% CI −5.2% to −1.3%; P<0.001). No statistically significant effect was found on self- reported (marginal odds ratio 1.07, 95% CI 0.58 to 1.98; P=0.82) or registered covid-19 infection (effect estimate and 95% CI not estimable owing to lack of events in the intervention arm).

Conclusion Wearing a surgical face mask in public spaces over 14 days reduces the risk of self-reported symptoms consistent with a respiratory infection, compared with not wearing a surgical face mask.

Trial registration ClinicalTrials.gov NCT05690516.

(SNIP)

Conclusion

Wearing surgical face masks is superior to not wearing surgical face masks in reducing the risk of respiratory symptoms over 14 days. The effect size was moderate, but wearing a face mask is a simple intervention with low burden and of relatively low cost and is one of several public health and social measures that may be worth considering for reducing the spread of respiratory infections.

What is already known on this topic

• The effectiveness of face masks as a protective measure against infection is uncertain

• Observational studies suggest that face masks reduce the risk of respiratory tract infections

• (and its limitations)Findings from randomised trials are, however, highly uncertain owing to methodological limitations such as insufficient statistical power

What this study adds

• Our pragmatic trial provides evidence that wearing surgical face masks in public spaces reduces the incidence of self-reported respiratory symptoms consistent with respiratory infections in real world settings

• Unlike most earlier trials of face mask, our study was sufficiently powered

• Similar trials can and should be conducted for other public health and social measures

       (Continue . . . .)

 

While I personally would opt for a KN95/N95 mask over a surgical mask (assuming I had the choice), a nearly 30% reduction in illness is nothing to sneeze at.