Seroepidemiology of Chlamydia pneumoniae TWAR infection in Seattle families, 1966-1979.

Incidence rates of Chlamydia pneumoniae infection and information on reinfection and transmission within families were obtained by serologic study of serum samples from prospective family studies conducted 1966-1979. Specimens (n = 3671) from 343 subjects in 68 families were tested for TWAR antibody using the microimmunofluorescence assay. Acute infection was defined as a fourfold rise in antibody titer between consecutive specimens. Sixty-four episodes of infection were identified in 58 persons; 4 had 2 infections and 1 had 3. From late 1975 until early 1979, when 3 serum specimens were collected yearly, rates of infection by age groups 0-4, 5-9, 10-14, 15-19, and greater than or equal to 20 years were 0, 9.2, 6.2, 2.2, and 1.5/100 person-years, respectively. Reinfections, defined as infections in persons with previous antibody, constituted most acute infections among adults. Acute infections more often affected a single family member than multiple members, but 2 or 3 family members were infected during the same period 12 times.