Experiments on the spread of colds: 1. Laboratory studies on the dispersal of nasal secretion

Abstract

An attempt has been made to study quantitatively the mechanisms by which infectious materials may enter the body by the upper respiratory tract and be shed during a cold.The rapid clearance of tracers, spores of B. mycoides and bacteriophage type T3, has been measured after adding them in small drops to the nose, conjunctiva and mouth.Tracers placed in the nose pass rapidly down the throat, but are found in only small amounts in the saliva. They are dispersed by blowing the nose and, more efficiently, by sneezing. Nearly all are shed as coarse droplets. About 0·1% are shed in droplets small enough to remain airborne and just over half of these are in the size range likely to be trapped in the upper respiratory tract. The droplets are apparently formed mainly in the nose. The larger amounts of droplets formed in the mouth carried relatively few infectious particles.Testing by experiments in a model system it was concluded that most of the coarse droplets produced by a sneeze or by an experimental spray fall rapidly to the floor. A few of the larger droplets were trapped on a moistened microscope slide intended to mimic the possible trapping of droplets on the conjunctive. The spores in these represented only a small proportion of those found in droplets which remained airborne and were collected by an air sampler.We wish to thank Miss P. D. Ball for technical assistance and Dr J. E. Lovelock for helpful discussion in the early stages of this work. We are also grateful to Sir Victor Negus and Dr B. Wyke for discussing the physiology of the nose with us, and to Mr K. R. May for his advice on methods of air sampling. The air samplers were loaned by the Microbiological Research Establishment, Porton, and the photographs taken by the Chemical Defence Experimental Establishment, Porton.