1.The results are reported of a study cases of pneumonia, of upper respiratory indection and of family contacts of cases of pneumoia for evidence of influenza-virus infection between October 1947 and April 1949.
2. During an inter-epidemic period in relation to influenza, two sporadic cases of influenza-virus A infection were detected, one in a case of pneumo-coccal pneumonia and the other in a family contact of a case of pneumonia. These were the only instances of virus infection detected amoung 158 individuals including seventy-eight cases of pneumonia.
3. The epidemic of influenza from February to April 1949 was associated with an increase in number of notified cases of pneumonia, particularly in those over 45 years of age compared with the notifications in 1948. Deaths from pneumonia also increased, particularly in those of 65years or over.
4. During the period of influenza prevalence, direct tests of specimens in eggs and serological tests gave positive evidence of influenza prevalence, direct tests of specimens in eggs and serological tests gave positve evidence of influenza virus A infection in many instances. Twenty-six of forty-one cases of upper respiratory infection between February and April 1949 were positive for influenza A and one was a case of influenza B.
5. Eifgteen of fifty-five cases of pneumococcal and staphyococcal pneumoniaccal and staphylococcal pneumonia, eight of fifteen cases of bronchitis, one of two cases of bronchiectasis and four of six cases of congestive heart failure gave serological or cultural evidence of influenza virus A infection during the period of February to April 1949.
6. The mechanism of influenza-virus infection in relation to bacterial infection of the lower respiratory tract is discussed.