Variations in the clinical pattern of experimentally induced colds

Abstract

An analysis has been made of the records of 5290 attendances at the Common Cold Research Unit, Salisbury, during the years 1946 to 1957. Materials prepared from the nasal washings of persons suffering from colds were administered to 993 volunteers, of whom 386 (38·9 %) showed definite evidence of infection within a few days. The attack rate of these experimentally induced colds was lower during the months October to March than from April to September. The difference was statistically significant as regards male but not as regards female volunteers.Six strains of virus were propagated by passage from volunteer to volunteer, in one instance up to the eighth serial transfer from the original material, without apparent loss of pathogenic properties. Comparison of the clinical effects of these strains, and of a number of miscellaneous strains, revealed several differences which were minor in character but, statistically, highly significant. These comprised differences in attack rate, severity, incubation period, duration and relative frequency of symptoms, which could not be ascribed to seasonal or other influences.It was concluded that the observed variations in the clinical pattern of the experimentally induced colds were attributable to qualitative differences in the strains of virus used.I wish to thank Sir Christopher Andrewes, F.R.S., for his unfailing help and encouragement at every stage of this investigation and all my colleagues at the Common Cold Research Unit for much useful comment and discussion. I am indebted to the Statistics Department of the Ministry of Labour and National Service for processing the records and to Mr R. G. Carpenter for assistance with some of the statistical analyses.