The isolation of an indifferent streptococcus (Number 344) from the lung of a fatal case of primary atypical pneumonia has recently been reported (1) and its biological properties described. Convalescent sera from more than onehalf of the cases of atypical pneumonia which were tested agglutinated this strain in final dilutions ranging from 1:10 to 1: 160 whereas agglutination in low titers occurred only rarely in the acute phase sera of such cases, in sera of normal individuals, or in acute or convalescent sera from persons with other respiratory diseases. The results of the streptococcal agglutination tests in atypical pneumonia correlated in many instances with the results of cold hemagglutination tests and with complement fixation tests with mouse lung antigen (2). In a number of cases, however, positive results were obtained with only one or two of these tests. Similar strains were also isolated from other cases.The authors did not feel that their evidence warranted the conclusion that the bacterium is a factor in the etiology of primary atypical pneumonia. Nevertheless, the fact that the positive findings were restricted largely to cases of atypical pneumonia is of some interest. The present paper deals with the results of serological tests in cases of atypical pneumonia and of other conditions using streptococcus 344 and another similar strain (E. S.) isolated in this laboratory. Tests for cold hemagglutinins were also done in all of the sera included in this study.
MATERIALS AND METHODSA total of 255 sera from 78 cases of atypical pneumonia and 330 sera from 163 other individuals were used in this study. The latter include serial specimens from 6 cases of rheumatic fever and 82 individual sera from non-rheumatic carriers and non-carriers of hemolytic streptococci. All of the rheumatic patients and a number of the others had recent streptococcal infections. The antistreptolysin titers of these sera were known. The sera and the antistreptolysin data were generously provided by Drs. T.Duckett Jones and Benedict F. Massell, of the House of the Good Samaritan, who had carried out repeated throat cultures in these cases. Antistreptolysin determinations were also carried out in their laboratory on serial specimens from a number of the cases of atypical pneumonia. The sera in the atypical pneumonias were tested after they had been stored from 3 to 15 months. All but a few of the remaining sera were tested within a few weeks of the time they were obtained.Streptococcal agglutinations were carried out in essentially the manner described by Thomas et al. (1). A transplant of strain 344 was obtained from Dr. Thomas and strain E. S. was isolated in December 1943 from a sputum obtained late in the disease in a characteristic and severe case of atypical pneumonia. It was found in almost pure culture in this sputum and it had cultural, biological, and serological properties similar to those of strain 344. The antigens were prepared by washing the sediment of broth cultures 3 times in saline arid then resuspending it in s...