ANDREWES 



noteworthy in unoccupied rooms. In crowded rooms where cross- 

 infection might be expected to occur, relative humidity is never 

 very low. 



What of temperature changes as causing changes in people's 

 habits ? Undoubtedly people tend to spend their spare time together 

 indoors in the winter and much more out of doors in summer. This 

 would tend to encourage spread of infection in winter - or so one 

 might at first sight suppose. But if one considers workers in offices, 

 factories, and shops (a considerable part of the population) , their 

 lives differ in summer and winter for only a small part of the day. 

 Many of them use crowded public transport all through the year and 

 they are perennially cheek-by-jowl in their shops, factories or of- 

 fices. Probably there is better ventilation in these surroundings in 

 the summer tims,butnothingachievedby students of air hygiene has 

 yet encouraged us to believe that respiratory infections are likely 

 to be greatly reduced by such means; nor yet by U-V irradiation, 

 chemical aerosols or other methods designed to give an equivalent 

 result. The fact is that as regards colds, the experimental evidence 

 available suggests that cross- infection takes place mainly through 

 direct hits with infectious particles at close range rather than 

 through minute droplet nuclei (Lovelock et al., 1952). So ventilation 

 could hardly be expected to play a major role. 



There are, of course, some circumstances in which particular 

 kinds of habit changes leadingto close aggregations certainly favour 

 spread of virus infections. Quite a number of viruses, som2 types of 

 adenoviruses, Coxsackie A 21 (or Coe virus), and Influenza B, all 

 cause outbreaks of respiratory infections mainly in recently col- 

 lected service recruits or in children re-assembling at boarding- 

 schools after holidays. Even here season plays a role, for the adeno- 

 virus outbreaks amongst recruits are not important during summer 

 months. 



We seem to be frustrated at every turn. Every promising clue 

 seems to peter out. Are recent advances in knowledge about colds 

 and other viruses likely to be able to help us? I think they are. First 

 of all, Tyrrell and his colleagues at Salisbury (Tyrrell et al., 19 59) 

 have found out how to cultivate viruses from a high proportion of 

 common colds in adults. These we are calling Rhinoviruses (nose- 



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