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Airborne infection in hospital

1982; Elsevier BV; Volume: 3; Issue: 3 Linguagem: Inglês

10.1016/0195-6701(82)90042-1

1532-2939

G.A.J. Ayliffe, E. J. L. Lowbury,

Indoor Air Quality and Microbial Exposure

Before the era of microbiology certain diseases were thought to be caused by noxious exhalations (‘miasmata’) arising from putrescent organic matter. Gregory (1788), for example, placed miasmata at the head of his list of ‘general causes of fever’, and also included among these causes ‘a certain state of the air which produces epidemical fevers, from causes not always ascertained’. The transfer of infection through the air, which had been recognized on epidemiological grounds, gained support at the beginning of the microbiological era from Pasteur’s demonstration that the sterilized contents of narrow-necked flasks became contaminated by bacteria admitted with air which was sucked in through the neck; the bacteria could be kept out by a cotton wool plug. Pasteur also showed that bacteria were abundant in the air of populated environments but scanty in mountain air or uninhabited rooms. The airborne transfer of bacteria and other microbes from an infected person or some other source, causing disease in previously uninfected persons, can occur only if the pathogens are expelled to the exterior in sufficient numbers, if they are able to survive in a virulent condition outside the body for an appreciable time, and if they are then able to gain access to and multiply in the susceptible tissues of a potential host. Tubercle bacilli were recognized in the early days of bacteriology to have such properties; Cornet reported in 1889 that they could survive in dried sputum and held that tuberculous infection was transmitted on dust particles arising from dried sputum (Wilson and Miles, 1975). Flugge (1899) held that droplets expelled from the respiratory tract were important vehicles; such droplets could be projected by a sneeze to a distance of several feet before they fell to the ground, and might cause infection if inhaled by someone within range. A third way in which microbes were envisaged to cause airborne infection was when they were carried as droplet nuclei (Wells and Wells, 1936), i.e. particles consisting of the residue left after evaporation of water from minute droplets which remained suspended in air. Dispersal may be promoted by sneezing and, to a lesser degree, by coughing (Lidwell, 1974); few organisms are dispersed during ordinary breathing or talking (Duguid, 1946). The numbers of organisms dispersed by different people when talking is variable, but a sneeze could disperse as many as 105-lo6 droplets.