Enumeration of air-borne bacteria in hospital.

An investigation of the "normal" bacterial content of the air of a large general hospital is described. In many different places within five different areas 70 to 200 settle-plate or slit-sampler bacterial counts were carried out. Average counts were most often of the same order as or lower than other published results and were proportional to human activity. The use of the logarithms of the counts showed no advantage, and conventional statistics should be applied with caution in evaluating such studies. Slitsampler and settle-plate counts of all bacteria showed no correlation, whereas those of Staph. aureus were correlated. There is a lack of parallelism between hospital infection and air bacteria counted by current methods, which are, therefore, not suitable for routine use.