1. In two R.A.F. recruit stations between November 1958 and March 1959, there were 2603 admissions to Sick Quarters with respiratory illness. Throat swabs from 1129, and paired sera from 1197 were tested for certain respiratory viruses.
2. From the serological results it was estimated that 19% of the admissions were associated with influenza A infection, 7% with influenza B, 26% with adenovirus, 1% with para-influenza Type 1, 1% with para-influenza Type 3 and 8% with Coe virus, but as 21% of the identified infections were multiple the proportion of illness associated with one or more of these infections was only 50%. Thirty-four per cent of the Coe virus infections and 56% of the para-influenza virus infections were multiple.
3. Virus isolation test results led to a similar estimate of the frequency of adenovirus infection (23%) but to a lower estimate for Coe virus (3%) and for the para-influenza viruses, no systematic attempt was made to isolate influenza viruses. Reasons are given for thinking that most of the admissions associated with Coe virus infection in 1958, but few of those in 1959, were caused by this agent. The proportion of illnesses attributable to viruses of the para-influenza group was probably about 1%.
4. The main symptoms associated with Coe virus infection were upper respiratory. Hoarseness was rather more prominent than in other infections but the height and duration of fever and the frequency of febrile symptoms were less. The few illnesses associated with para-influenza virus infection had no obvious distinguishing features.
1. Blood specimens were taken from 205 recruits on their arrival at a recruit camp in January 1960 and immediately before their departure in March; 764 men in ten operational stations were bled in January and a sample of 260 were bled again in March.
2. The respiratory illness admission rate was 25% in the recruits and 4% in the trained men; 49% of the recruits showed a rise in antibody to one or more respiratory virus antigens compared with 2% in the other group. The high rate of infection in recruits was mainly due to adenovirus (36%) and Coe virus (20%).
3. It was estimated that about a third of the adenovirus infections and an eighth of the Coe virus infections were responsible for illness requiring admission. There was no indication that either infection caused any appreciable number of less severe illnesses not requiring admission.
4. Evidence from this survey and the earlier one suggests that the presence of neutralizing antibody to Coe virus does not prevent infection, though it appears to lower the probability of illness.