We've talked here fairly often (see, for example, here) that the way and how far influenza virus spreads isn't understood or known precisely. That seems to be a big surprise, not only to the public but to many in the public health community who should know better. That's why I was pleased to see that this dirty little secret is finding its way into the public press (hat tip from one of our many readers in Oz, RobT):
It was a simple question: how far could a virus spluttered out of someone's mouth travel?When Professor Lidia Morawska went looking for an answer, she was staggered to find little research on this important health issue. Only three studies existed. "And the results were contradictory."
So her team at Queensland University of Technology built a machine to measure the distance a droplet moves in air before drying out, depending on whether people are coughing, spitting or laughing.
It had been thought that if you were an arm's length from an infected person you were safe, Professor Morawska says. "But we found the droplets evaporate quickly and the dried residue can travel large distances." (Sydney Morning Herald)
This doesn't mean an influenza virus can travel long distances and remain replicable. This was (apparently) a question about the fate and transport of large droplets that are coughed or breathed. At what point in the change in volume of the droplet is the virus no longer viable? Maybe the answer is very quickly or maybe it is that the virus remains viable long after the droplet reaches a size where it can remain suspended for hours or days and can be breathed deeply into the respiratory tract. You'd think we would know the answer to this by now.
But we don't.
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Humidity is much lower during flu season. Droplets would get smaller faster.
Darwin: Lots of thing have been looked at, but it wouldn't explain why we don't have flu in the southwest at other times of year or other places where the humidity is low. It is a real puzzle. See our earlier post, linked in this one.
Excellent posts -- I'd never considered these aspects of influenza transmission. The fall forecast for the southern US this year is warmer and drier and than normal. Does that increase the potential for outbreaks?
I guess my big question would be simple. How long have viruses been around and how come the medical types are just getting around to checking this one?
It sure explains a lot of things.
Revere/Tom DVM does this in your opinion with the stuff being in bird poo put that 3km exclusion zone around poultry farms into question after an outbreak. Was there anything available in print regarding the viability of the virus at the "hundreds of meters" range?
I see humidity isn't good for encapsulated viruses, yet you claim (some) dry climates may limit transmission.
Hmm. I wonder how much aerosolized viruses charge, and how they aggregate with other particles in dry environments?
In any case, if aerosolized virus transmission is shown to work, there should be a lot of interesting transport problems to look at.
Randy: This is very hard to study and the tools to study it haven't existed. That's the explanation.
Torbjorn: I don't know the role of humidity. I am just noting that for every idea there are counterexamples.
Very interesting article in the Sydney Morning Herald, thanks RobT.
Some of the article even fit in with yesterday's post on biodefense labs.
wake-up calls about the importance of biosecurity have been coming thick and fast.
highlights how human error can have disastrous consequences.
We should always be concerned about sophisticated containment labs, because there can be one moment of carelessness. Vigilance is crucial.
This line at the end of the article, "drop in the ocean", was well placed as the article's point was centered basically on spray travel: What happened to the horse industry is a drop in the ocean of what could occur with other diseases.
So now we have to wonder about the dried residue as well.
It's interesting too as mankind cannot control everything that the universe hurls at us. We'd like to think we can but in truth we cannot.
Revere-Sitting down and thinking this thru a bit am I correct in saything that "this changes everything?" If BF is technically airborne now along with all of the other nasties out there, every protocol that the HCW's have followed for years has to be changed, correct? If someone even comes thru the door of a hospital and has BF or really just about any respiratory type of viral disease, they are going to have to come up with something to keep them from honking it everywhere.
Someone with a moderately screwy disease could infect a hospital and take the whole place out. I can only imagine what someone with BF that is undiagnosed could do. Suspected cases would have to be kept out on the street and only brought inside in full isolation/quarantine and with the accompanying procedures that go with it.
This kind of sets things back on its ear for a while. I swear though, I would have thought that the medical types would have done this study sooner. Its perfect in its simplicity but so many questions get answered, and now we dont like the answer.
Randy: It's the same situation as ordinary flu. One person with flu won't infect a hospital or your house or anything else. A hospital might add some UV light to ERs or isolation areas but other than that it's another airborne respiratory virus like RSV, flu, parainlfuenza, etc. This changes nothing, really.
Equine Flu has spread from a quarantine station(!) in Sydney (means of spread unkown) to infect 12000 horses and 1200 properties in NSW alone in the last couple of months despite the best efforts of vets, public, and govt officials alike. Emergency planning and a freeze on all horse movements was in place within 4 or 5 days from the first case being notified. Interestingly, it hasn't crossed the border into Victoria as yet. It was in Qld within 2 weeks. I heard today one of the senior racing officials calling for vaccination because as far as he was concerned containment just wasn't working.
As a complete amateur but interested observer, I'm both surprised and unsurprised by this post and the comments: surprised that so little is known about the spread, unsurprised, because that lack of knowledge explains what I consider bizarre lack of planning for public volunteer involvement in coping with an epidemic. After headlines a couple of years ago, I read Crosby's history of 1918 and took away two things: 1) a hospital is the last place you want the ill to line up at the door, except for the most serious cases; and 2) the cities that had among their "leading citizens" the best organizers (who were not necessarily or even likely to be existing officials) came through the epidemic the best. Both criteria made me glad I'll be in Detroit should a pandemic happen.
mle.detroit: It will be interesting to see who will shine appropriately when the pandemic hits. Many valuable lessons to be learned and god willing, remembered and applied by those who survive.
There is concern about being in a city though.
The gangs, thieves, robbers, and those desperate enough that would do anything to survive. It could get very ugly, very quickly.
What I found interesting about this article was the idea that aerosolation of H5N1 was possible coupled with the work from several years ago that showed that the virus was viable on hard surfaces for at least 48 hours, I believe. Presumably the fomite mode of transmission would indicate that the virus would remain viable as the droplets evaporated and dispersed?
The next phase of Dr. Morawska's work seems to indicate they will be examining this issue, which addresses the core issue: Is H5N1 viable and infectious in aerosol form? Yes it's surprising this hasn't been answered to date, given the stakes.
Hope not !