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Masking or Not Masking for Flu?

Bidirectional transmission of influenza A virus between pigs and people is an on-going challenge faced by the swine industry and public health. The challenge arises from the unpredictability of swine influenza infections becoming zoonotic and, in some instances, turning into a human pandemic, as was the case in 2009 when the H1N1 influenza pandemic virus emerged.

Also, the frequent spillover of human-origin seasonal influenza viruses to pigs is a main driver for flu diversity resulting in new reassortant viruses that threaten pig health, productivity and public health. Once these “new” reassortants are in pigs, they have the potential of causing disease when transmitted back to people. Despite these well-known risks, little is done at the pig-human interface to prevent these interspecies infections.

Use of personal protective equipment including disposable gloves, coveralls, goggles and face masks is recommended to mitigate exposure to flu virus in pigs. Face masks are recommended to decrease aerosol exposure. The flu virus can be found in the air and deposit in the worker’s respiratory tract.

However, levels of PPE use varies among farms and activities in part due to lack of comfort wearing them which is particularly noticeable for face masks. N-95 respirators are considered the standard for preventing exposure to viral aerosols since 95% of airborne particles are captured in the respirator. However, tight fitting of the respirators to the face of the user is necessary for particles to be removed and not by-pass the seal. Unfortunately, N-95 respirators are difficult to keep in place when performing certain chores common at the farms and environmental conditions with elevated temperatures and humidity make wearing the N-95 respirators particularly uncomfortable.

Other masks such as dust masks and surgical masks may also be used in farms. However, there is limited information available on their effectiveness on protecting workers against flu at the farms.

In a recent study sponsored by the National Pork Board, we compared levels of flu virus in nasal passages of workers wearing different types of face masks and compared the results to not wearing masks. We evaluated N-95 respirators, dust masks and surgical masks and workers wore them as they usually do as part of their routine chores. Workers were given general instructions on how to wear them but they were not fit tested.

Our results indicated that wearing a mask decreased the detection of flu virus in the workers. Participants not wearing masks had the most influenza virus detections (24.27%), which was significantly higher (p<0.01) than all the detection rates for all three masks types (10.98% surgical mask, 8:33% dust mask, 5.77% N-95 mask). However, there were no statistically differences in flu virus detection rates between the three masks types (p>0.05). Among masks, workers reported that surgical masks were the most comfortable to wear.

In summary, our results add to the evidence that flu exposure through aerosols is common in swine farms and supports the use of face masks as an intervention strategy to decrease the risk of flu virus transmission at the workers and swine interface. Understanding which face mask is more comfortable to swine workers should increase the likelihood of wearing them. Collectively results from this study should help design more effective interventions to prevent flu transmission at the human and animal interface.

[Source: National Hog Farmer 8 October 2024 by Montse Torremorell, DVM, University of Minnesota, Department Chair, Professor, Department of Veterinary Population Medicine]