While the ways that influenza can be transmitted have been pretty well described (direct contact, airborne large-droplets, airborne small aerosols & fomites), the relative risks of becoming infected by each mode - which undoubtedly varies by environments and scenarios - is less well understood.
The mechanics of influenza transmission are likely different in an office, than in a classroom, a hospital waiting room, or aboard a train or an airplane.During a severe flu season - or more importantly, during a pandemic - understanding how flu is transmitted in various environments will be crucial in designing `barriers' to help limit transmission.
In the past we've looked at some of the modes of flu transmission, including:
Study: The Role Of Aerosols In The Spread Of InfluenzaICAAC Video: How Quickly A Virus Can Spread In A Building,
Formidable Flu Fomites
Pre-Symptomatic Transmission Of H1N1 Influenza In the Ferret Model
we looked at an experiment on fomite transmission, which they described as:
Using tracer viruses, researchers found that contamination of just a single doorknob or table top results in the spread of viruses throughout office buildings, hotels, and health care facilities. Within 2 to 4 hours, the virus could be detected on 40 to 60 percent of workers and visitors in the facilities and commonly touched objects. Simple use of common disinfectant wipes reduced virus spread by 80 to 99 percent.We've even seen evidence that viruses may be aerosolized via a more circuitous route (see NIOSH Video: Adventures In Toilet Plume Research). We followed up this report with new studies last February (see Toilet Bowl Sunday).
But I digress . . .We've a new study, published today in the International Journal Environmental Research & Public Health, that attempts to quantify how an influenza A virus might be transmitted in a specific office setting (12 × 8.4 × 2.7 m with 39 students) over a 5 day period.
Since there are ethical (not to mention recruiting) problems involved in exposing an office full of people to a live flu virus, a number of assumptions, and substitutions for a virus, had to be made.
The authors describe their methods as:
In this study, we simulated influenza A transmission in a graduate student office by considering three routes: long-range airborne, fomite and close contact (short-range airborne and droplet spray). All student behaviour, including close contact and surface touches in the office, was recorded by video-camera from 9 a.m. to 9 p.m., from 11 to 15 September 2017. The data included more than 3500 close contacts between students and more than 127,000 surface touches. Influenza A transmission was simulated in the office via three routes based on realistic behaviour obtained from these recorded data.
First a link, the abstract, and some excerpts from a fairly lengthy (and math heavy) study (bolding mine) - then I'll return with a postscript.
Transmission of Influenza A in a Student Office Based on Realistic Person-to-Person Contact and Surface Touch Behaviour
Nan Zhang and Yuguo Li *
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
Received: 2 June 2018 / Revised: 3 August 2018 / Accepted: 7 August 2018 / Published: 9 August 2018
(This article belongs to the Special Issue Health-Related Emergency Disaster Risk Management (Health-EDRM))
Influenza A viruses result in the deaths of hundreds of thousands of individuals worldwide each year. In this study, influenza A transmission in a graduate student office is simulated via long-range airborne, fomite, and close contact routes based on real data from more than 3500 person-to-person contacts and 127,000 surface touches obtained by video-camera.
The long-range airborne, fomite and close contact routes contribute to 54.3%, 4.2% and 44.5% of influenza A infections, respectively. For the fomite route, 59.8%, 38.1% and 2.1% of viruses are transmitted to the hands of students from private surfaces around the infected students, the students themselves and other susceptible students, respectively.The intranasal dose via fomites of the students’ bodies, belongings, computers, desks, chairs and public facilities are 8.0%, 6.8%, 13.2%, 57.8%, 9.3% and 4.9%, respectively. The intranasal dose does not monotonously increase or decrease with the virus transfer rate between hands and surfaces.
Mask wearing is much more useful than hand washing for control of influenza A in the tested office setting. Regular cleaning of high-touch surfaces, which can reduce the infection risk by 2.14%, is recommended and is much more efficient than hand-washing.
Influenza A transmission in a graduate student office is simulated via long-range airborne, fomite, and close contact routes based on realistic data of human behaviours. The long-range airborne, fomite and close contact routes contribute to 54.3%, 4.2% and 44.5% of influenza A infections, respectively.
For the fomite route, 59.8%, 38.1% and 2.1% of viruses are transmitted to the hands of students from private surfaces around the infected students, the students themselves and other susceptible students, respectively. The private surfaces of infected students are highly contaminated.
The quantity of virus (TCID50) is much higher on the private surfaces around the infected student (approaching 800 times) than around susceptible students. Keyboards, headphones, desktops, mice and mobile phones are the five most-contaminated private surfaces around the infected student.
Public surfaces are dirtier than the private surfaces of susceptible students. The intranasal dose via fomites of the students’ bodies, belongings, computers, desks, chairs and public facilities are 8.0%, 6.8%, 13.2%, 57.8%, 9.3% and 4.9%, respectively. The intranasal dose does not monotonously increase or decrease with the virus transfer rate between hands and surfaces, and a specific value setting can optimally limit influenza A virus transmission via fomites
(Continue . . . )
Mask wearing is much more useful than hand washing for control of influenza A in the tested office setting, and the total risk can be reduced from 8.75% to 0.45% if an N95 mask is tightly sealed by infected students. Regular cleaning of high-touch surfaces, which can reduce the infection risk by 2.14%, is recommended and is much more efficient than hand-washing.
As the authors point out, there are a lot of assumptions made (particularly, since no actual flu virus was used or measured), and no shortage of limitations, in this study. To wit:
This study has various limitations. All students are assumed to stay in the office at all times except at lunch and dinner time, virus generation is overestimated, and a higher infection risk of susceptible students is calculated. The virus transfer rate between surfaces and hands is influenced by many factors, such as force, area and touch duration.
We assumed that each touch between a specific surface and a hand has the same transfer rate. Most particles are deposited on the desktop when the infected student talks, coughs or sneezes, and we did not consider that some private things such as mice, keyboards and cups share the virus on the desk. Therefore, the quantity of virus (TCID50) on the desk is overestimated.
Moreover, in our simulation, some parameters such as transfer rate between hand and various surfaces are not based on influenza virus due to data unavailability. Heterogeneity exists in the study, and it may result in some errors. The differences in human behaviour by gender are ignored, and relative positions, heights and angles between two students during close contact are not considered.
A future study should collect some samples in the office if any students are infected with influenza A. We can then compare the real virus distribution data with our simulation data to verify the accuracy of our model.Despite these formidable limitations, this study does suggest that the airborne route is more of a transmission risk than fomites, and that the use of N95 masks could help reduce transmission more than hand washing.
The issue of N95 mask use by the public during an influenza pandemic opens a big can of worms, as they will almost certainly be in very short supply, and will be needed desperately for Health Care Workers who will be in daily direct contact with infectious patients.N95 masks, used improperly - or without prior fit-testing (see Survival Of The Fit-tested) - are unlikely to provide any better protection than paper surgical masks, even if you can get them.
Neither provide guaranteed protection, and are only part of a layer of protective steps you should take, including avoiding exposure, washing hands frequently, and getting the flu vaccine when it is available.But for those who'd like to have the option of using surgical masks during the next pandemic (or severe flu season) - buying them now, while supplies are plentiful and their cost is minimal (< .10 each) - is probably your best course of action.
Just don't expect them to be a panacea for a pandemic.