by revere, cross-posted from Effect Measure

I’m just getting around to reading the Brief Report by Blachere et al., “Measurement of airborne influenza virus in 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).


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 they 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.


  1. #1 Bill Borwegen
    March 13, 2009

    I am glad to report that the following US House Report language inserted by Congresswoman DeLauro took effect this week when President Obama signed the 2009 Omnibus Appropriations Bill. Organized labor actively participated in the deliberations and issuance of the referenced IOM report that provided the basis for seeking these funds. We are hopeful that this research will lead a better understanding of the airborne transmission of the influenza virus and to the development of a new generation of advanced respirators and other personal protective equipment to increase both safety and comfort for nurses and other healthcare workers who must wear these products to protect themselves from a wide range of airborne biological threats while they work to provide quality patient care. Bill Borwegen, SEIU

    Page 76 of the House Statement:

    “According to a report issued in 2008 by the Institute of Medicine of the National Academies, there is a critical need to better understand the airborne transmissibility of pandemic flu and other pathogenic bioaerosols to protect healthcare workers and to gauge the efficacy of the currently recommended types of respirators. The bill includes $3,000,000 within the total for Personal Protective Technology for NIOSH to research modes of transmission of influenza and to evaluate filtering face piece respirators, other types of respirators, and other personal protective equipment. Further, NIOSH is urged to design and promote the next generation of personal protective equipment for healthcare workers and first responders to address the unique challenges posed by the healthcare environment.”

  2. #2 revere
    March 13, 2009

    Bill: You are completely correct. I’ve drafted a post for Effect Measure which comments on this to appear tomorrow morning.

  3. #3 Bill Borwegen
    March 13, 2009

    The langauge is pretty much verbatim what we at SEIU drafted for Congresswoman DeLauro. The original request was for $8 million, but $3 million is a good start. In this case earmarks can be a very good thing.

  4. #4 MM
    April 27, 2009

    I’m not a doctor, but I have a thought on the subject for what it’s worth. Though my friends think I’m crazy, defying conventional scientific wisdom, I’ve been skeptical about how transmittable ariborne flu viruses are in open air, esp. outdoors. So this paper caught my attention. Not to dismiss that, esp in closed areas like school classrooms for instance, but my attention is directed to the potential mode of transmission thru eating establishments, or whereever food is involved and people get together. Perhaps we are eating contaminated food more than we realize is the gist of my hypothesis here. I believe I have experienced this first hand myself being sick with influenza (not food poisoning) on a few occassions. I noticed that in many situations were the occassion is to share a meal with others, a house, a restaurant, etc, there is often at least one person sick. Often it’s the cook, the waitress bringing the plate of food, or if a potluck, or salad bar, any number of diners can transmit their germs to the community food. I also observe patrons of eating establishments, and poor manners as it is, quite often people eat with their fingers, that is they have to smack the food off their fingers, then their fingers are everywhere else. I’ve seen them dunk their fingers in salad bars as well. I’ve witnessed a whole family, adults and kids, all with a cough, and all sticking their fingers in their mouths, and then their hands touch tables, chairs, etc. I recently contacted a mild cold or flu, and I believe I can trace the source to a cook in one of the local fast foods. Last year I got a good dose of the flu and I believe I traced that to a potluck of about 30 people, and I was the last to serve myself from the food pot. Recently the cashier in the grocery store was sick I noticed, and thought that every bit of food that I buy may have some of her germs on it. To conclude, I suspect that flu and cold transmission via areas of served food may be contamintated by either cooks, servers or patrons, and that perhaps this moded is a widely underestimated mode of transmision. If that can be of any help whatsoever so much the better. Mark Miller
    April 27 2009