A Study of Mycoplasma Pneumoniae Infections in Families

Epidemiologic and serologic studies were performed on 25 families in which there was a case of Mycoplasma pneumoniae infection. Intrafamilial spread of infection occurred in 24 of these families. The group studied comprised 107 members. M. pneumoniae was isolated from 71% of 45 children and from 53% of 62 adults. Half of these cases continued to shed the microorganism for more than 4 weeks and 4 cases for two and a half to 4 months after onset of illness. M. pneumoniae persisted in the throat even after treatment with tetracyclines or erythromycin. A 4-fold increase in complement fixing, tetrazolium reduction inhibiting or indirect haemagglutinating antibodies and/or recovery of M. pneumoniae were considered evidence of infection. According to these criteria 70 cases (65%) were infected. Another 9 persons (8%) were classified as cases of probable infection. Pneumonia occurred in at least 30% of 54 infected contact cases and in at least 51% of all infected family members, index cases included.