The transmission and clinical manifestations of infection with Mycoplasma pneumoniae were studied in 114 families in which there was a case of atypical pneumonia. M pneumoniae was isolated from a throat culture of the index pneumonia patient in 36 of these families. Transmission to other family members occurred in 23 of the 36 families. In these 23 families, 84% of the children and 41% of the adults were infected. The index cases are included. Of the total 59 patients with family-contact infections, 42 had lower-respiratory-tract symptoms, 6 had pharyngitis alone, 9 (all children) were asymptomatic, and 2 had probably unrelated symptoms. The time intervals between cases within a family suggested a median incubation period of 23 days. Treatment with tetracycline seemed neither to cure the symptoms completely nor to abolish the carrier state that often lasted one to three months.
Hjordis M. Foy, J. Thomas Grayston, George E. Kenny, E. Russell Alexander, Ruth McMahan. Epidemiology of Mycoplasma pneumoniae Infection in Families. JAMA. 1966;197(11):859–866. doi:10.1001/jama.1966.03110110083019