Swine Flu in San Diego

[Rolfe]

I wasn't commenting on a recommendation for or against the masks. I was commenting on Rolfe's statement, "I've just pocketed a couple of the proper disposable respirators we use at work when sampling swan casualties for possible avian influenza. These things really do keep out viruses ".

My comment was based on the fact that these respirators are issued to those of us working up close and personal with bird cadavers being checked for possible avian flu (and as the entire world knows, one of these cadavers actually turned out to be positive). Our H&S guys are absolute tyrants, so I suspect the masks do the job.

I've had to do one of these "face-fit" tests for using the respirators, and if I picked up correctly what was going on, it was shown to keep out formaldehyde vapour when fitted properly.

Rolfe.

 

[DaN K. StAnLeY]

Holy Crap! I really need to get going on my insurance

 

[Skeptic Ginger]

It's not true, at least any more: a 2-year old child just died of it in Texas.

One child with pre-existing health problems isn't enough to change the "if true" I was referring to. It doesn't change the fact the age pattern of deaths is unusual.

 

[Skeptic Ginger]

My comment was based on the fact that these respirators are issued to those of us working up close and personal with bird cadavers being checked for possible avian flu (and as the entire world knows, one of these cadavers actually turned out to be positive). Our H&S guys are absolute tyrants, so I suspect the masks do the job.

I've had to do one of these "face-fit" tests for using the respirators, and if I picked up correctly what was going on, it was shown to keep out formaldehyde vapour when fitted properly.

Rolfe.

The vapors are being absorbed by an active filter of some kind either charcoal or an ion filter mechanism. Such a category of mask would have a time limit on it because one cannot tell if the filter is saturated by sight.

However, masks with these vapor filters still only have mechanical filtration for particulates >1 micron. Some masks even say 1-5 micron size particulates. If the particulate filter size were smaller, you could not suck air molecules through the mask efficiently.

The influenza A virus, in its spherical form, is about 120 nm, intermediate in size for a virus.

Here's a fun animation demonstrating this scale. Hit the > repeatedly to go smaller and smaller and to see a micron vs a nanometer.


When it comes to PPE, OTOH, what matters is do people wearing it get infected? I am not suggesting the mask is insufficient for protecting you in the setting you use it in. And when it comes to influenza, most often it is only spread in droplets, not airborne virus particles. Evidence shows the masks are effective in most influenza hazard situations, even surgical masks. The real key is handwashing and keeping your hands, if contaminated, out of your face.

BTW, I just found a reference indicating influenza virus lives 24-48 on surfaces when the conditions are right.

 

[Ivor the Engineer]

Cool animation.

 

[Soapy Sam]

Listening to an exchange of opinions on BBC radio about this reminded me of Terry Pratchett's line that "From an arrow's point of view, chain mail is essentially a loosely connected series of holes".
On the scale of a virus, a dfust mask would resemble a mesh of open barn doors.
I wonder how much finer the non-particulate surgical type masks are?

 

[Dymanic]

On the scale of a virus, a dust mask would resemble a mesh of open barn doors.

What counts is not the scale of the virus, but the scale of the droplet carrying the virus -- unless you posit that naked virions are a significant component of the material ejected by coughing or sneezing. That may be theoretically possible, and evidence for small droplet transmission is not nonexistent; it just isn't as compelling as evidence for large droplet transmission.

If one insists on seeing protective measures as either foolproof or useless, then there really isn't much one can do to protect against influenza, short of going into total isolation. I prefer to think in terms of biasing the odds in one's favor, even if it is only slightly. Take a number of precautions -- each of which is slightly effective -- and you may end up with a level of protection you can call good enough.

 

[Skeptic Ginger]

What counts is not the scale of the virus, but the scale of the droplet carrying the virus -- unless you posit that naked virions are a significant component of the material ejected by coughing or sneezing. ....

I read a number of studies when looking at this issue earlier. In the majority, flu followed a droplet pattern. But in one or two studies it followed an airborne pattern.

I was going to hunt for the articles anyway, but you'll have to give me a minute or two.

 

[Dymanic]

I read a number of studies when looking at this issue earlier. In the majority, flu followed a droplet pattern. But in one or two studies it followed an airborne pattern.

I was going to hunt for the articles anyway, but you'll have to give me a minute or two.

I seem to recall that you and I had a rather invigorating go-to over this maybe a couple of years ago.

 

[BillyJoe]

Your 2 minutes were up a couple of hours ago.

BTW, what happened to Deetee re that 1976 vaccine?


EDIT:
WHO classification raised from phase 4 (person to person spread) to phase 5 (pandemic imminent).

 

[ElMondoHummus]

Juxtaposition imposes much meaning

can cats catch this?

i have already purchased 60 surgical masks...=)

For the cats??

 

[Skeptic Ginger]

I seem to recall that you and I had a rather invigorating go-to over this maybe a couple of years ago.

Could be. What was your position on the subject then?

 

[kellyb]

I can't find anything about it on the CDC site (yet, it might be in tomorrows press briefing) but an MSNBC article I read said that Mexican baby who died? His parents were completely without any symptoms whatsoever. Considering the fact that this virus is being found all over the western world now, I don't think that means it's a matter of transmissibility. It seems to imply that something similar or something with cross-reactive immunity has circulated before.

I'm not sure what to think yet, but I'm apparently in agreement with Dymanic.
Earlier I was reading over this pretty comprehensive Hilleman paper he wrote in 2002 on the facts and mysteries of influenza A in humans:

http://biomicro.sdstate.edu/WangX/Micr425/Pathogenesis/Influenza_A.pdf

And there are a few interesting points worth sharing with those who don't already know.
(I haven't checked out the original research because this is coming from Maurice Hilleman, who had a tendency to generally be correct about these things.)

It was calculated [65] that the influenza-associated mortality
in the US numbered 69,800 persons in the 1957–1958
pandemic event, and 33,800 persons in the 1968–1969 pandemic.

So, "pandemics" (shouldn't we come up with a better word for this? "Zoonotic years" or something?) aren't necessarily a lot worse (or worse at all) than regular flu seasons.

Also:

The appearance of a new HA in each pandemic virus typically
marks the dominance of the new virus and the disappearance
of the previous one. The pandemic of 1918–1919
was caused by an H1N1 virus, the origin of which is now
being explored (see Section 7.2). According to Scholtissek
et al. [26], the 1947 pandemic H2N2 virus was derived by
reassortment of H1N1 with an unidentified virus (probably
avian) in which new H2, N2, PB1 (see [27]) and PA genes
were acquired. The 1968 pandemic H3N2 virus was derived
through reassortment exchange of the H3 component for the
H2 of the parent H2N2 virus. The reappearance and worldwide
spread of virus subtype H1N1, which was the cause for
the “Russian pandemic” virus of 1977, 20 years following
its disappearance after 1957, is considered to be both aberrant
and remarkable [28,29]. Genetic analyses showed the
1977 Russian isolate [28,29] to be of near genetic identity
with the H1N1 viruses that were circulating in 1950. This
indicates that the virus had been preserved at some undefined
location, probably in frozen storage [28]

So I wonder if the presence of our currently circulating H1N1 might somehow repress the emergence of a new one? Or is 100 years not long enough to observe trends that shouldn't be strongly suspected of being mere coincidence?
Or could this new pig H1N1 "push out" the New Caledonia H1N1 circulating now? Or could we get a lot of both circulating next fall?

Another:

In these studies, it may be hoped that new and evolving
antigens of viruses may be detected in nature before they
pose problems for people [140]. The emergence of H3N2
reassortant influenza viruses in North American pigs [141]
and its rapid antigenic drift [92] provide a basis for concern.
There is also the observation of antigenic heterogeneity
among H1N1 swine influenza isolates [156] and the recent
report of death in a woman from zoonotic H1N1 influenza
of swine origin [142]. All of this demonstrates the immense
genetic flexibility of influenza viruses and the problem of
accurate prediction of events to come.
The 1997 Hong Kong avian influenza occurrence and the
response to it made H5N1 “the mouse that roared”. Cohen
[143] declared it the “flu pandemic that might have been”.

Looks like Hilleman was right, huh?

 

[Skeptic Ginger]

Your 2 minutes were up a couple of hours ago.

BTW, what happened to Deetee re that 1976 vaccine?....

Well naturally there are more studies now and I had to read them ... ALL, then there was dinner, then the Daily Show.....

So it looks like there are a few more studies documenting influenza aerosols. Figures, just when I need confidence I'm writing policies that actually are supported by the data. And of course, there is no Cochrane review on respirator use. Health care worker safety always takes a back seat to disease research.


PRO FLU IS AIRBORNE, NOT JUST DROPLET SPREAD:

Measurement of Airborne Influenza Virus in a Hospital Emergency Department.

Blachere M, et al

Size-fractionated aerosol particles were collected in a hospital emergency department to test for airborne influenza virus. Using real-time polymerase chain reaction, we confirmed the presence of airborne influenza virus and found that 53% of detectable influenza virus particles were within the respirable aerosol fraction. Our results provide evidence that influenza virus may spread through the airborne route.

Inactivation of influenza A viruses in the environment and modes of transmission: a critical review.

Weber TP, Stilianakis NI.

OBJECTIVES: The relative importance of airborne, droplet and contact transmission of influenza A virus and the efficiency of control measures depends among other factors on the inactivation of viruses in different environmental media. METHODS: We systematically review available information on the environmental inactivation of influenza A viruses and employ information on infectious dose and results from mathematical models to assess transmission modes. RESULTS: Daily inactivation rate constants differ by several orders of magnitude: on inanimate surfaces and in aerosols daily inactivation rates are in the order of 1-10(2), on hands in the order of 10(3). Influenza virus can survive in aerosols for several hours, on hands for a few minutes. Nasal infectious dose of influenza A is several orders of magnitude larger than airborne infectious dose. CONCLUSIONS: The airborne route is a potentially important transmission pathway for influenza in indoor environments. The importance of droplet transmission has to be reassessed. Contact transmission can be limited by fast inactivation of influenza virus on hands and is more so than airborne transmission dependent on behavioral parameters. However, the potentially large inocula deposited in the environment through sneezing and the protective effect of nasal mucus on virus survival could make contact transmission a key transmission mode.

THIS ONE USES CONFUSING TERMINOLOGY BUT THEY INCLUDE A DEFINITION. They use the terms 'droplet transmission' and 'contact transmission' interchangeably.

Quantifying the routes of transmission for pandemic influenza.

Atkinson MP, Wein LM.

Motivated by the desire to assess nonpharmaceutical interventions for pandemic influenza, we seek in this study to quantify the routes of transmission for this disease. We construct a mathematical model of aerosol (i.e., droplet-nuclei) and contact transmission of influenza within a household containing one infected. An analysis of this model in conjunction with influenza and rhinovirus data suggests that aerosol transmission is far more dominant than contact transmission for influenza. We also consider a separate model of a close expiratory event, and find that a close cough is unlikely ( approximately 1% probability) to generate traditional droplet transmission (i.e., direct deposition on the mucous membranes), although a close, unprotected and horizontally-directed sneeze is potent enough to cause droplet transmission. There are insufficient data on the frequency of close expiratory events to assess the relative importance of aerosol transmission and droplet transmission, and it is prudent to leave open the possibility that droplet transmission is important until proven otherwise. However, the rarity of close, unprotected and horizontally-directed sneezes-coupled with the evidence of significant aerosol and contact transmission for rhinovirus and our comparison of hazard rates for rhinovirus and influenza-leads us to suspect that aerosol transmission is the dominant mode of transmission for influenza.

Notice that while they claim aerosols are likely, they stick to the conclusion droplet spread should be assumed until further studies are done. From the standpoint of facing a risk, I'd think it should be the other way around.


N95s SPECIFICALLY ADDRESSED USING A TEST VIRUS, RESULT, N95 NOT SUFFICIENT:

Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks?

Bałazy A, Toivola M, Adhikari A, Sivasubramani SK, Reponen T, Grinshpun SA.

BACKGROUND: Respiratory protection devices are used to protect the wearers from inhaling particles suspended in the air. Filtering face piece respirators are usually tested utilizing nonbiologic particles, whereas their use often aims at reducing exposure to biologic aerosols, including infectious agents such as viruses and bacteria. METHODS: The performance of 2 types of N95 half-mask, filtering face piece respirators and 2 types of surgical masks were determined. The collection efficiency of these respiratory protection devices was investigated using MS2 virus (a nonharmful simulant of several pathogens). The virions were detected in the particle size range of 10 to 80 nm. RESULTS: The results indicate that the penetration of virions through the National Institute for Occupational Safety and Health (NIOSH)-certified N95 respirators can exceed an expected level of 5%. As anticipated, the tested surgical masks showed a much higher particle penetration because they are known to be less efficient than the N95 respirators. The 2 surgical masks, which originated from the same manufacturer, showed tremendously different penetration levels of the MS2 virions: 20.5% and 84.5%, respectively, at an inhalation flow rate of 85 L/min. CONCLUSION: The N95 filtering face piece respirators may not provide the expected protection level against small virions. Some surgical masks may let a significant fraction of airborne viruses penetrate through their filters, providing very low protection against aerosolized infectious agents in the size range of 10 to 80 nm. It should be noted that the surgical masks are primarily designed to protect the environment from the wearer, whereas the respirators are supposed to protect the wearer from the environment.

CON, DROPLET SPREAD IT IS, NOT AIRBORNE (Apparently now in the minority of the study results, Psst, don't anyone tell CDC, it is not a PC point of view since there is no practical solution.) :

Transmission of influenza A in human beings.

Brankston G, Gitterman L, Hirji Z, Lemieux C, Gardam M.

Planning for the next influenza pandemic is occurring at many levels throughout the world, spurred on by the recent spread of H5N1 avian influenza in Asia, Europe, and Africa. Central to these planning efforts in the health-care sector are strategies to minimise the transmission of influenza to health-care workers and patients. The infection control precautions necessary to prevent airborne, droplet, and contact transmission are quite different and will need to be decided on and planned before a pandemic occurs. Despite vast clinical experience in human beings, there continues to be much debate about how influenza is transmitted. We have done a systematic review of the English language experimental and epidemiological literature on this subject to better inform infection control planning efforts. We have found that the existing data are limited with respect to the identification of specific modes of transmission in the natural setting. However, we are able to conclude that transmission occurs at close range rather than over long distances, suggesting that airborne transmission, as traditionally defined, is unlikely to be of significance in most clinical settings. Further research is required to better define conditions under which the influenza virus may transmit via the airborne route.

AND ANOTHER INTERESTING RELATED MEASURE OF AIRBORNE TRANSMISSIBILITY:

Human HA and polymerase subunit PB2 proteins confer transmission of an avian influenza virus through the air.

Van Hoeven N, et al

The influenza virus genes that confer efficient transmission of epidemic and pandemic strains in humans have not been identified. The rapid spread and severe disease caused by the 1918 influenza pandemic virus makes it an ideal virus to study the transmissibility of potentially pandemic influenza strains. Here, we used a series of human 1918-avian H1N1 influenza reassortant viruses to identify the genetic determinants that govern airborne transmission of avian influenza viruses. We have demonstrated that the 1918 HA gene was necessary for efficient direct contact transmission, but did not allow respiratory droplet transmission between ferrets of an avian influenza virus possessing an avian polymerase subunit PB2. The 1918 PB2 protein was found to be both necessary and sufficient for airborne transmission of a virus expressing the 1918 HA and neuraminidase. Also, it was found that influenza viruses that were able to transmit efficiently in ferrets were able to replicate efficiently at the lower temperature (33 degrees C) found in the environment of mammalian airway. These findings demonstrate that the adaptation of the HA and PB2 proteins are critical for the development of pandemic influenza strains from avian influenza viruses.

 

[Dymanic]

CONCLUSION: The N95 filtering face piece respirators may not provide the expected protection level against small virions.

RECOMMENDATION (mine): If you can't avoid possible exposure altogether (best), then wear the mask, and don't expect it to provide 100% protection.

 

[Perpetual Student]

Intentionally or unintentionally, the media typically lacks perspective in reporting on catastrophes, diseases, etc. Regarding swine flu:

There is one confirmed US death (a boy with other "complications") so far.

Now, here is the daily average mortality by some selected causes in the US:

Car Accidents: 122
Other Accidents: 158
Homicide and firearm injury: 165

That's a small proportion of the 6,706 daily deaths (year 2002 figures) in the US. To provide some perspective, I chose the above causes because they are generally not related to aging and disease. So, if we add up all those figures and multiply by 365 we get 162,425 annual deaths out of a total of nearly two and a half million deaths per year.
We have a very long way to go for this swine flu to become a serious concern for most of us.
That is not to say that effective measures should not be taken by governments to prevent a pandemic. I am saying that the media coverage lacks perspective.

 

[casebro]

Here's another thought:

The Spanish Flu epidemic of 1918 killed off those with the "cytokine storm gene". Those of us alive now are more immune to that aspect of diseases. Evolution at it's finest.

 

[Dymanic]

Here's another thought:

The Spanish Flu epidemic of 1918 killed off those with the "cytokine storm gene". Those of us alive now are more immune to that aspect of diseases. Evolution at it's finest.

The "cytokine storm" thing is still largely theoretical. Not sure a lot of people realize that. It's a nice fit to the available data and all, but there simply is not enough evidence to determine with any real degree of certainty whether that phenomenon was in fact the cause of the skewed age distribution curve in the Spanish Flu demographics. Smacking down the aggressive immune response with systemic corticosteroids appears tempting as a treatment option, and it has been tried, but for the most part without much success. Every time we master one lesson learned from influenza and move on to the next one, the first thing we learn is that half of what we learned during the last lesson was wrong.

 

[Puppycow]

I wonder if the labratory-confirmed deaths were also tested for AIDS?

Also, what were their ages and other medical conditions. I've only heard some vague assertions, but no data.
Wikipedia says that there are 12 confirmed deaths so far.

 

[Sparky]

Too many of us have been vaccinated against related strains for one thing.

I had the swine flu shot in the 70s, and if I were exposed I would likely have a much milder case.

I received a flushot when I was in the hospital for neck surgery at the end of March. I still came down with the flu (strain unknown) 2 weeks ago 2 days after my friend did. The worst symptoms passed in a day and I was back to work 2 days later.

Several of my co-workers have battled it since with no lasting effects. Since we live and work in San Diego, we were mildly concerned. Needlessly, it seems.