The prevalence and clinical pictures of Mycoplasma pneumoniae infections among children were studied using culture and serological techniques. The isolation rate was 22% (195 of 885) in pneumonic patients and 11% (66 of 600) in non-pneumonic patients. In patients three years of age or less, M. pneumoniae was isolated at the same rate from febrile and afebrile cases and from wheezy and non-wheezy cases. In older patients, however, M. pneumoniae was frequently isolated from febrile but non-wheezy cases. A peak in the number of the positive isolates was found in patients who were four years old. The peak number of M. pneumoniae infections at age four was confirmed serologically. This peak was in patients who were younger than those previously reported.

Allergic predisposition among infants with bronchiolitis was examined. The number of infants with serum IgE exceeding mean +1 SD was 31/70 (44.3%). The rate of positive radioallergosorbent test (RAST) scores of 1 or more to mites, egg white, or milk was 31/71 (43.7%) and that of scores over 2 was 11/71 (15.5%). Eosinophils and/or mast cells were found in their nasal smears on several occasions. These results indicated that allergic predisposition may be observed among infants with bronchiolitis.

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