An epidemic often provides an opportunity to obtain evidence of the etiologic association of a microorganism with disease. Chlamydia pneumoniae TWAR is a newly recognized organism whose relationship to disease is not completely understood. An outbreak of C. pneumoniae infections from November 1990 to February 1991 was studied in University of Washington students. Twelve TWAR infections were identified serologically in 54 students with acute respiratory disease. The organism was isolated from 7 of the 12 and identified by the polymerase chain reaction (PCR) in 2 that were isolation-negative. The organism was not found in any of the 42 serologically negative patients or in 51 control student patients without respiratory illness cultured in 1991. There was no evidence of infection with Mycoplasma pneumoniae or respiratory viruses in the 12 patients with C. pneumoniae infection. During the 4-month outbreak, there was an increase in total pneumonia cases. These findings provide evidence for an etiologic association of C. pneumoniae with pneumonia and bronchitis.

Attendance at large day care was associated with more common colds during the preschool years. However, it was found to protect against the common cold during the early school years, presumably through acquired immunity. This protection waned by 13 years of age.

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.

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Objective.\p=m-\Tostudy the consequences of delayed first childbearing in a large, population-based US sample, with separate analysis of women aged 40 years or more and adjustment for socioeconomic factors, smoking, medical and reproductive conditions, and route of delivery.Design and Setting.\p=m-\Retrospectivesurvey of Washington State birth certificates from 1984 through 1988. Subjects.\p=m-\First liveborn singleton infants of women aged at least 20 years. Of eligible white infants, all those born to women aged 35 to 39 years (n=4019) and 40 years or more (n=410) and a maternal age-stratified random sample of white infants of younger women were studied. All eligible black infants were studied.Outcome Measures.\p=m-\Low (<2500 g) and very low (<1500 g) birth weight and preterm delivery (<37 weeks of gestation).Results.\p=m-\Adjusted odds ratios for delivering a low-birth-weight white infant increased progressively with each 5-year maternal age group, reaching 2.3 (95% confidence interval, 1.6 to 3.4) for women aged 40 years or more compared with those aged 20 to 24 years. The maternal age effects for very low birth weight and preterm delivery were similar; for each, the odds ratio was 1.8 for the oldest group. No significant maternal age effect was found among births of black infants, but only 127 births to women aged 35 years or more were studied.Conclusion.\p=m-\Increasing maternal age at first childbirth is an independent risk factor for low birth weight and preterm delivery of white infants in the United States. (JAMA. 1993;270:2574-2577