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Quiz time…. Airborne Contagious Diseases

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How many airborne contagious diseases exist?  No one knows the precise answer to that question, so let me give you an easier one.  How many airborne contagious diseases are recognized by the CDC?1 Let me give you your options:
a. 3
b. 30
c. 300
d. 3,000

What do you think? The answer is actually a!  Now for a follow-up question.

What are the three recognized airborne contagious diseases?
a. Legionnaires disease, pontiac fever, and hypersensitivity pneumonitis
b. Aspergillosis, valley fever, and histoplasmosis
c. Influenza, common cold, SARS
d. Chicken pox, tuberculosis, and measles

The right answer is d!  That may surprise you.  Answers a and b include airborne diseases that are not contagious.  I’d bet most people guessed c.  Although these agents will travel through the air for a short time, their transmission is not classified as being airborne strictly speaking. More on that in a minute.  The correct answer is d because chicken pox, tuberculosis and measles are all contagious and have an airborne transmission route.

Are you still upset, thinking that c is a valid answer?  We need to distinguish between large droplet transmission and airborne transmission.  Large droplets are generated when an infected individual talks, coughs or sneezes.  The large droplets are traditionally thought to be greater than 5 microns in diameter and travel less than a meter.  True airborne transmission occurs when the infectious agents travel on smaller particles, less than 5 microns, for greater distances.  These small particles are called droplet nuclei.  They form when the saliva or sputum they were traveling on evaporates.  They are therefore the dried residual of respiratory droplet.

The current mainstream thought is that influenza, common cold and SARS are transmitted through large droplets, and chicken pox, tuberculosis and measles are transmitted through droplet nuclei.  I will say this… there is some compelling evidence that influenza, common cold and SARS may all be able to travel in the air beyond a meter.

If you got the two quiz questions correct, let me know in the comments section!  Have a great weekend!

  1. Center for Disease Control and Prevention, 2007 Guideline for Isolation Precautions-Preventing Transmission of Infectious Agents in Healthcare Settings []

By Ian Cull

I'm I.A.N. the Indoor Air Nerd. I'm a speaker and consultant on indoor air quality issues. To learn more about me, click "about" at the top of this page.

One reply on “Quiz time…. Airborne Contagious Diseases”

November 2010;

Measurements of Airborne Influenza Virus in Aerosol
Particles from Human Coughs
William G. Lindsley1*, Francoise M. Blachere1, Robert E. Thewlis1, Abhishek Vishnu2, Kristina A. Davis3,
Gang Cao1, Jan E. Palmer4, Karen E. Clark4, Melanie A. Fisher3, Rashida Khakoo3, Donald H. Beezhold1
1 Allergy and Clinical Immunology Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, West Virginia, United
States of America, 2 Department of Community Medicine, West Virginia University, Morgantown, West Virginia, United States of America, 3 Department of Medicine, West
Virginia University, Morgantown, West Virginia, United States of America, 4 Well WVU Student Health, West Virginia University, Morgantown, West Virginia, United States
of America

Influenza is thought to be communicated from person to person by multiple pathways. However, the relative importance of
different routes of influenza transmission is unclear. To better understand the potential for the airborne spread of influenza,
we measured the amount and size of aerosol particles containing influenza virus that were produced by coughing. Subjects
were recruited from patients presenting at a student health clinic with influenza-like symptoms. Nasopharyngeal swabs
were collected from the volunteers and they were asked to cough three times into a spirometer. After each cough, the
cough-generated aerosol was collected using a NIOSH two-stage bioaerosol cyclone sampler or an SKC BioSampler. The
amount of influenza viral RNA contained in the samplers was analyzed using quantitative real-time reverse-transcription PCR
(qPCR) targeting the matrix gene M1. For half of the subjects, viral plaque assays were performed on the nasopharyngeal
swabs and cough aerosol samples to determine if viable virus was present. Fifty-eight subjects were tested, of whom 47
were positive for influenza virus by qPCR. Influenza viral RNA was detected in coughs from 38 of these subjects (81%).
Thirty-five percent of the influenza RNA was contained in particles .4 mm in aerodynamic diameter, while 23% was in
particles 1 to 4 mm and 42% in particles ,1 mm. Viable influenza virus was detected in the cough aerosols from 2 of 21
subjects with influenza. These results show that coughing by influenza patients emits aerosol particles containing influenza
virus and that much of the viral RNA is contained within particles in the respirable size range. The results support the idea that the airborne route may be a pathway for influenza transmission, especially in the immediate vicinity of an influenza patient. Further research is needed on the viability of airborne influenza viruses and the risk of transmission.

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