COLD AND COLDS 



second peak early in the New Year, and, less regularly, a third 

 lower peak about March. The New Year peak corresponds to the 

 favourite period for Influenza A epidemics. There are very many 

 differences between summer and winter, not only in temperature 

 and humidity, but in resulting changes in our habits, our dress, and 

 our diet; and it is extremely difficult to pin-point any one of these as 

 responsible for the winter increase in colds. Undoubtedly, a fall in 

 temperature precedes an outbreak of colds, but low temperature as 

 such does not do so; it is the change that matters. Milam and Smillie 

 (1931) found that onthe tropical island of St. John,the daily variation- 

 over a range of 6.5° C- was the same as the difference between the 

 summer and winter maxima (6.5° C to 8° C) ; yet colds were virtu- 

 ally absent from late May to late October. They thought that with 

 smaller temperature changes, colds were both scarcer and milder 

 than in colder climates. Van Loghem in Holland (1928) and also ob- 

 servers in North America have recorded that outbreaks of colds 

 occur simultaneously over wide areas of thecountry.lt is very dif- 

 ficult to explain this on any theory of simple per son-to- person 

 spread. The outbreaks seem rather tobe precipitated by temperature 

 changes. 



Several writers consider thatrelativehumidity is more important 

 than temperature. Hemmes et al. (1960) reported that the virus of 

 influenza, a winter infection, survived better in the air under con- 

 ditions of low than of high humidity, whereas the virus of poliomj^e- 

 litis, a summer disease, behaved in an opposite manner. Hope 

 Simpson (1958) has pointed out that with the onset of colder weather, 

 people light fires indoors, or turn on the central heating, thus 

 causing a considerable drop in relativehumidity. At just such times 

 he sees in his practice a sudden increase in upper respiratory in- 

 fections. He does not venture to suggest whether this could be due 

 to better survival of viruses in the air, as Hemmes' results would 

 indicate, or to some effect onthe host's resistance. The effect on 

 virus survival seems unlikely, for rhinoviruses or common cold 

 viruses are closely related in their fundamental properties to the 

 enteroviruses, which include poliovirus; and their stability at various 

 relative humidities resembles that of the poliomyelitis rather than 

 of the influenza virus. So on Hemmes' line of reasoning, colds 

 should be a summer disease. Further, the fall in relative humidity 

 which Hope-Simpson records as happening in the autumn, is only 



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