Effect Measure

I’m just getting around to reading the Brief Report by Blachere et al., “Measurement of airborne influenza virus i a hospital emergency department” (Clinical Infectious Diseases 2009:48:483-440) but it’s quite interesting. We’ve noted fairly often here that we still don’t know for sure what the main modes of transmission of influenza are, something that surprises many people. We “know” that flu can be passed from person to person via the respiratory secretions from runny noses, coughs and sneezes but we often don’t think more deeply about this. We know that viral material can remain viable on inanimate surfaces like doorknobs and arm rests for long periods (maybe days), but we don’t know how often this kind of exposure results in actual infection. As for the virus passing through the air between people, we don’t know if this is through the rather large particles easily visible with coughs and sneezes, particles which are quite heavy and settle out quickly within a few feet or most of the source and aren’t breathed deep into the lungs; or much via the much smaller aerosols that can remain suspended in the air for long periods (perhaps days) and penetrate easily into the depths of the lungs. You can see immediately how the size of the droplets might make a difference. If you go into a hospital emergency room during flu season, are you only likely to get infected if you sit next to an actively shedding flu patient in the waiting room or is the air of the waiting room full of floating flu virus? The paper by Blachere et al. set out to measure the sizes of floating aerosols containing viral material in the air of a hospital emergency department at the height of the 2008 flu season (February).

i-1f86b45c082dc0fefcda1a589d758e18-cough.jpg

The study design was straightforward but carrying it you was technically demanding. Stationary aerosol samplers were set up on tripods at various places and at various heights for six afternoons in the emergency department of the West Virginia University Hospital (Morgantown, West Virginia is also the location of an important laboratory of the National Institute of Occupational Safety and Health, NIOSH, experts in measuring contaminants in workplace air). Seven ER docs also wore personal aerosol samplers for 3 – 4 hours (each was tested for flu first to ensure they weren’t the source of any detected viral material). The aerosol samplers were able to distinguish the sizes of the particles: > 4 microns, 1 – 4 microns, and < 1 micron. Particles greater than 4 microns are still respirable if they are also less than 10 microns or so, while the other two sizes are both respirable and will remain suspended in the air for long periods. The collected material in the three size ranges then underwent PCR to see if there was genetic material indicative of flu virus (the primer was from the well conserved M1 matrix protein gene of the flu virus).

Usable data was available from four of the six sampling days and on three of the four genetic material from flu virus was detected. Almost half (49%) were from the two stages of sampling for sizes less than 4 microns, i.e., definitely in the respirable and suspended particle range. Some of the particles larger than 4 microns would also be in that category, but the data in the paper does not permit me to say how much. We know that many of the particles released in sneezes, coughs, talking and normal respiration are in the 4 – 1- micron range, however. None of the samplers in two examination rooms had positive results, but there were positive samples from the Waiting, Reception and triage Rooms, while three of the four ER docs had positive results in their personal samplers.

This is the best information we have to date about influenza A (there wasn’t enough influenza B to study) and where it is in the environment of a health care facility during flu season. But there is a great deal still to learn. Finding viral genetic material does not completely settle the issue. We don’t know if the viral genetic material detected was part of a replicable virus or not, which is critically important. And while information on humidity, temperature and barometric pressure were collected, there were not enough samples to be able to assess the effect of the environment on viral prevalence in the air. This paper shows that the difficult task of measuring and sizing viral aerosols in a health care environment is possible, in itself a major advance.

This is another small piece of a very big puzzle. We don’t have to have every last piece in place but there are large areas where we can see hardly any of the main features, and transmission was one of them. Science is usually slow, but with sufficient resources, it is steady.

Comments

  1. #1 Frank Mirer
    March 13, 2009

    I wonder about the sizing of water droplets – as water evaporates the droplets shrink until only the non volatiles are left, although there’s likely water absorbed into the non volatiles. The actual impactor sizing would be sensitive to the density of the particle, an opening which excludes >2.5 micron mineral particles I think allows >2.5 micron water droplets.

    Also, particles up to 100 microns are “inhalable” – capable of being deposited in the upper airway, where their viral burden might also be infectious. I don’t know the inlet diameter on these aerosol samplers, but the typical closed face filter cassette excludes particles greater than 10-12 microns, even though these may be the large majority of the aerosol mass.

  2. #2 revere
    March 13, 2009

    Frank: You are right that the water evaporates and makes smaller particles. That is one of the ways small virus containing particles are generated. What matters it their aerodynamic behavior and that is what is being measured by the sampler. Regarding respirable versus non respirable, it makes a difference in understanding how flu is transmitted. The dynamics of infection for different inoculation sites is different: different defenses, different host cells, etc., and the kind of personal protection is also different. Even an N95 mask may not work well for very small particles, whereas a surgical or dust mask might work for the large ones. For large droplets the distance you can be infected by someone else is maybe a meter whereas for small particles just being in the room hours later might be sufficient. For reasons you suggest, measuring the size of viral particles is technically subtle, so the NIOSH folks have made an advance IMO.

  3. #3 Larry Ayers
    March 13, 2009

    Your statement “Science is usually slow, but with sufficient resources, it is steady.” is sort of a variation of the old saw “The mills of the gods grind slowly, but they grind exceedingly small.”

  4. #4 Lea
    March 13, 2009

    revere: “And while information on humidity, temperature and barometric pressure were collected,”
    How important are these?

    When I read that it reminded me of my gall bladder removal operation and how amazingly cold the operating room was.

  5. #5 revere
    March 13, 2009

    Lea: “And while information on humidity, temperature and barometric pressure were collected,”

    How important are these?

    We don’t know. Data with guinea pigs implied that low humidity was important for transmission but in the Nicaraguan study the peaks were during the summer rainy season. We just don’t know.

  6. #6 Racter
    March 14, 2009

    Yesterday, I returned to the ER where I was treated on Tuesday for a spontaneous pneumothorax. (It takes a lot to get me anywhere near such a place at this time of year, but a collapsed lung will do it). The Heimlich catheter valve they had fitted me with had done its job, and I couldn’t wait to get it removed, because it was rather uncomfortable. Actually though, I found that I could wait. For hours.

    The discomfort from the catheter was nothing compared to the discomfort of spending several hours in the same room with people who were obviously ill, but I didn’t see a choice. I could have waited outside (it was a gorgeous sunny day), but when they came to call me in, they’d figure I had bailed. The lady at the information desk looked like she needed somebody to talk to (and she looked healthy enough), so I went over and just sort of conversationally mentioned that the one piece of information I’d most like to have is why it is that an immunocompromised person like myself (due to the massive pred dump I recieved the other day) has no choice but to sit in a room with people who are sick enough that hospital staff have had to provide them with blankets to keep them from being too chilled while they wait to be treated. She thought that was a pretty good question. She didn’t have an answer, but she did have a solution: she asked my name, and offered to come outside and get me when they called. Sometimes the simplest approach is the best.

    Questions about airborne transmissibility of (say) influenza and how that is influenced by particulate size, humidity, temperature, etc — are interesting, and important. But do we really need to wait for definitive answers before taking the simplest and most obvious steps toward better infection control, such as providing separate waiting areas for infectious (or immunocompromised) patients? Seems like a no-brainer to me.

  7. #7 paiwan
    March 14, 2009

    “But do we really need to wait for definitive answers before taking the simplest and most obvious steps toward better infection control, such as providing separate waiting areas for infectious (or immunocompromised) patients? ”

    It’s important to manage the common waiting area by providing the efficient ventilation. What I mean the efficient ventilation is constantly sucking out the air and efficiently dilutes the viral load in the waiting area.

    The design should be not difficult; the cool air pump into the waiting room from four bottom corners, install heater in the room, the central top has a upside down funnel to suck out the air, warm air supposedly on the top. The edge of the funnel can install UV lights. Make sure the air in and out no mixing.

    Perhaps periodical ozone injection (under safety level) in the air inlet will help.

    My experiences in dealing with aquatic viral infections have taught me that the worst condition in a confined tank is the diseased vector. See a shrimp pond has birds standing in the pond side (Bird is smart to spot the dead shrimp and flying down to pick the weak or dead shrimp.) The day’s evening the whole pond’s shrimp will be wiped out. Viral infection and contagion is very very speedy in water borne when the diseased vectors exist.

    I think that the waiting room is a dangerous place. And it needs new design.

  8. #8 Don Milton
    March 14, 2009

    Nice to see some discussion on my current favorite research topic. You may be interested in a paper we pulished in PLoS ONE last summer showing that 1/3 of flu patients in a small sample in Hong Kong have detectable viral RNA in the fine particles they exhale. We also recently showed in another PLoS ONE paper that viral aerosols (in this case vaccinia — yes done with “Biodefense” dollars) can be very efficiently inactivated in air using upper room UVC. Some emergency rooms (e.g. Brigham and Women’s in Boston) use upper room UVC air disinfection in the waiting areas. However, to my knowledge none take advantage of the added effect of using ceiling fans shown in the PLoS ONE paper. Next time you go to the ER, look and see if there are any of those strange louvered fixtures casting a beam of UVC across the top of the room. They may be much more effective than just simple ventilation.

  9. #9 revere
    March 14, 2009

    Don: Thanks for the reference. We’ve discussed the possible use of UV for flu here before, although I’ve not seen any data on its efficacy for this (just TB and now your vaccinia cite). Do you have any views on the viability of the virus when detected in this way?

  10. #10 paiwan
    March 14, 2009

    1. UV is a very powerful disinfecting tool, especially UVC designed for germicidal. The only problem is maintenance, the bulb surface is easy to have dust or (mold is water), constant cleaning by scrubbing, nowadays have automatic cleaning device.

    2. I think that air flow thru ventilation is better than circulation ventilation; circulation ventilation is mixing the air, so the virus is evenly distributed and disinfected by UVC for instance, while the one- way flow thru is effectively reducing the viral load. Our body temperature is high, so exhaled air from lung is higher than the room air and it will ascend. With the constant addition of cool air from the bottom, the room air will be one way flow thru. The top UVC installation will kill germ and prevent it comes down viable. What do you think?

    3. Ozonation is also very powerful. Some restaurants install in food storage and preparing areas and reduce the food contamination diseases greatly. So, it deserves the research into this tool.

  11. #11 daedalus2u
    March 15, 2009

    paiwan, if you look at the papers linked to in Don Milton’s comment, the limits of air treatment external to the room become clear. The cost of air changes is roughly proportional to the number of changes per hour (that reflects heat load or air conditioning load). Adding UV units put a big multiplier on the attenuation of viral load, equal to large multiples of air changes per hour. Some pretty simple baffles might greatly improve this.

    Maintaining stratified air flow is pretty difficult. Any kind of movement of people in a room is going to cause mixing. I think that increasing the mixing to bring particulates into the exposure zone of the UV is a much better approach.

    There are compounds that when exposed to UV produce oxidative conditions on their surface. Titanium dioxide is such a compound. Organic compounds on such a surface exposed to UV will be oxidatively consumed. Most dust is organic. These compounds absorb UV, so their use on bulb surfaces would have to be quite limited. I think using UV for water treatment is difficult because inorganic compounds from the water can precipitate. Iron oxide for example, which very strongly absorbs UV.

  12. #12 LindaK
    March 15, 2009

    This discussion prompts me to ask a question I’ve had for a while now. It’s not specific to flu, but flu and colds. When, relative to onset of symptoms, is a person contagious? Does it wax and wane?

    I’m visiting a friend who is sick with a nasty cold and am wondering about the timing of being contagious.

  13. #13 paiwan
    March 15, 2009

    daedalus2u/ Don:

    The fan in addition to upper room UVC make the difference. Thanks for the comment.

    I stay in tropical area; I have not counted on the heating cost in this case.

    The number of patients in the emergency/ waiting room is another contributing factor; therefore optimal ACH could be calculated and adjusted.

    I am still curious about the feasible inclusion of ozone with UVC, say if the worst scenario of infection happens- like smallpox or H2H. Perhaps you’ve known that during SARS attack in Taiwan, medical people had died of being infected.

  14. #14 revere
    March 15, 2009

    LindaK: The answer will be different for different viruses and probably for different populations. There is good evidence that people can be shedding flu virus for as much as 24 hours before onset of symptoms, although the degree of shedding is less than when the person is coughing and sneezing, as should be obvious. Since there are several viruses causing “colds” I have no set answer nor do I know if we know. How long? It is probably reasonable to think that as long as someone is coughing, sneezing, etc., they are shedding virus, although the amount of viral load will probably decrease with time. How contagious they are is not well characterized. Not much help, but now you know we don’t know.

  15. #15 LindaK
    March 15, 2009

    Thanks, revere! I’ll go wash my hands again :-)

  16. #16 Maggie Brown
    March 16, 2009

    In the meantime, there are other preventative measures (besides vaccinations) to help stop the spread of the flu. And so far this year, there have been serious consequences. As young children are the #1 spreaders of germs, there is a great program out there called Germy Wormy Germ Awareness for Germ Transportation Vehicles, ages 2 – 7. It really works to teach children in a mom-invented and drug-free way to both avoid AND keep from spreading germs. Parents, schools and daycare centers are raving about it!
    http://www.germywormy.com Give kids a PLACE to give their germs instead of you!

  17. #17 paiwan
    March 16, 2009

    Revere:

    This post has pointed some implications in preventing flu infections in the public room (confined space). Perhaps it would become mandatory to have UVC and fan installed in crowded space, for instance long distance air-conditioned bus. In fact, the office exceeds certain number of people shall consider the installation. The cost is negligible, but the effect is substantial.

    The new personal lifestyle should be thoughtful enough to prevent to receive flu patient, phone greeting is enough. The patient receives the visitors, if necessary, should be not in the bedroom, and shall be a place with good ventilation, a good remainder though.

  18. #18 paiwan
    March 16, 2009

    I have an actual case for advices.

    My partner works in an international NGO project based in Phuket, Thailand. The project is a regional supporting office to help Burmese workers who are working in Phuket. The service items are in various, general clinic, special for TB treatment, HIV care and others. The doctors all are recruited from Burma.

    The problem here is the office design. It combines with clinic and offices. The site has two separate buildings called A. and B., but only 5 meters distance. A Building has three stories; ground floor is clinic where the patients are waiting, and the doctors in separate room but the same floor. The second floor is where doctors stay as administration for accounting, report and computer. The third floor is the general administrations which mix international staff.

    B. Building has only one floor where they use for TB patients treatments and waiting space which has only one wall, so the ventilation is very good.

    My partner told me that one of her colleague has been infected by TB who has happened to be the TB project staff and need to drive the patients coming to the clinic and home.

    The A Building’s 2nd and third floor have air-conditioned, I have noticed that staff have pretty higher rate of flu. Are there any recommendations that I could release to them and help them improving. This NGO usually is frugal in budget, but sometimes maybe put the first line project staff in risk.

  19. #19 paiwan
    March 16, 2009

    Addedum: The clinic is free charge for Burmese workers.

  20. #20 albatross
    March 16, 2009

    Does anyone know if the commercially-available HEPA filters for room air do any good with airborne viruses? Those are usually sold/recommended for allergies, but it seems like they might help with decreasing the concentration of virus floating around in a waiting room.

  21. #21 Lea
    March 17, 2009

    Don’t know albatross but personally I’d use ANY type of air filtration, including the HEPA ones.
    Since it’s obvious, at this point in time, that we can only count on our own self-knowledge I’d say it would be a good way to go. At least give it a shot.

  22. #22 anon
    March 21, 2009

    did height of tripod play a role ?

  23. #23 revere
    March 21, 2009

    anon: Not enough data.

Current ye@r *