Absurd experiment of the day: airborne transmission of colds

I have been spending much of my time recently working on a project for the National Air Filtration Association (NAFA). The goal is to review literature on the transmission of infectious diseases and explore what kinds of impacts that HVAC particle filters may have on the transmission of infectious aerosols. It’s a wonderfully interesting project that I’m happy to be working on. But it has also sent me digging into a world of literature that I previously didn’t know existed.

For example, I’ve known that there has been a long running debate about whether infectious diseases are transmitted primarily via (i) inhalation of airborne aerosols, (ii) contact with contaminated surfaces, or (iii) some imprecise mixture of the two. In digging in this field, I came across a paper today that details an amazingly absurd, yet extremely helpful, set of experiments.

Check out the following statement from Dick et al. (1987). Aerosol Transmission of Rhinovirus Colds. The Journal of Infectious Diseases. 156(3):442-448:

Twenty-seven to 34 men >18 years of age were inoculated intranasally with 560-2400 TCID50 of safety-tested RV16 [i.e., rhinovirus, or a virus that leads to the common cold] by pipette and spray on two successive days. On the third day, eight men with the most severe colds (donors) played stud and draw poker with 12 antibody-free … men (recipients) between the hours of 8 a.m. and 11 p.m.

Going on…

In experiments A-C the donors and six of the 12 recipients played cards naturally and used cloth handkerchiefs for secretion, cough, and sneeze control, whereas the remaining six recipients in each experiment wore devices that blocked completely all hand-to-head movements.

Did you catch that? A group of men were taken into a lab and injected with cold virus. Then the following day, those men were put together in a room with 12 healthy uninfected men where they played stud and draw poker all day long! The catch was that half of those healthy men were able to touch their faces and behave quite normally; the other half were restrained by these braces such that they couldn’t touch their faces!

This is such an absurd but beautifully constructed experiment to me. I don’t even know if you could get IRB approval for something like this any more. I can just imagine the conversation that led to this experiment. “What if we take a bunch of people, infect them, then make them play poker for 12 hours. Half the people they play poker with can blow their nose, touch their faces, etc., and the other half will be physically restrained — but only to the point where they can’t touch their face… they can still play cards!

In the end, their results are extremely important to the debate on airborne vs. surface transmission of disease. They reported no significant difference between the two groups, suggesting that aerosol transmission must have been the dominant route. Amazing!

Filed under: Experimental methods | Exposure measurement | Infectious disease | Particulate matter