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Seroepidemiology of Chlamydia pneumoniae TWAR Infection in Seattle Families, 1966-1979 Michael B. Aldous, J. Thomas Grayston, San-pin Wang, and Hjordis M. Foy
Departments ofEpidemiology and Pathobiology. University of Washington. Seattle
Chlamydia pneumoniae is a recently described third species in the genus Chlamydia that has been found to be a common cause of pneumonia and other respiratory infections in humans [I, 2]. Previous studies of C. pneumoniae, including most studies ofthe prevalence ofTWAR antibody, have used patient sera. Population incidence studies have not been done. This study has taken advantage of a unique serum bank from prospective family studies of respiratory infections conducted in the Seattle area during 1966-1979 by Fox et al. [3, 4]. Several prospective family studies of respiratory infections done before 1980 provide much of what we know ofthe epidemiology ofacute respiratory infections. Due to cost, however, it is unlikely that similar prospective studies will be done in the near future. This study provides information on the incidence of C. pneumoniae infection, the occurrence ofreinfection, and the transmission of the organism within families.
Methods Participants in the prospective family studies of respiratory infection were members of the Group Health Cooperative of Puget Sound. a large, prepaid health maintenance organization; participants were mostly white and middle class. Families in the Seattle Virus Watch (VW) study (1966-1969) were enrolled at the birth of a child [3]. Serum specimens were collected routinely twice per year and at times of illness. In 1972, 1973, and
Received 25 November 1992; revised 13 April 1992. Presented in part: 7th International Symposium on Human Chlamydial Infections. Harrison Hot Springs, Canada, June 1990. Grant support: National Institutes of Health (AI-21885). Reprints or correspondence: Dr. J. Thomas Grayston, Department of Epidemiology, SC-36, University of Washington, Seattle, WA 98195. The Journal of Infectious Diseases 1992;166:646-9 © 1992 by The University of Chicago. All rights reserved. 0022-1899/92/6603-0033$01.00
1974, members of some VW families gave yearly serum specimens for studies of influenza and Mycoplasma pneumoniae. The Seattle Family Flu (FF) study (1975-1979) included some of the original VW families and some new families; all had at least I child in elementary school [4]. Serum specimens were collected three times per year during this period. Stored sera from these studies were tested from two groups of families, those that participated in both the VW and FF studies and those that participated in only the FF study. Some members ofVW-FF families had specimens available from 1966 to 1979, except for 1970 and 1971. Intervals between successive serum specimens varied, especially between study periods; in addition, some specimens were missing or depleted. The proportions of specimens obtained from female and male subjects were approximately equal. For both groups, there were relatively few sera from children 60) are included. The median age was 39 years for male adults and 37 years for female adults.. Sera were tested for antibody in the immunoglobulin M and G (IgM and IgG) serum fractions using the microirnmunofluorescence technique [5] with TWAR antigen (strain AR-39) [6]. A fourfold rise in IgG titer between consecutive specimens was considered evidence ofacute infection. In other studies, a single IgM titer of ~ 16 or a single IgG titer of ~512 has been considered suggestive of acute infection. However, because the present study involved multiple serum collections unrelated to acute illness, this criterion was not used. Four persons had IgM antibody. In each, acute infection was independently demonstrated by fourfold rise in IgG titer. Of 8 specimens with an IgG titer of ~512, 6 were associated with antibody titer rises. The 2 other IgG titers of this magnitude were in subjects with sustained high antibody titers between 128 and 512, without a fourfold rise, and were not considered to indicate acute infection. Results of respiratory virus isolation and virus and mycoplasma serologic tests were available from the original studies [3, 4]. Denominators for incidence calculations were found by summing intervals between serum specimens within age groups. When a subject changed age groups between serum sample
Downloaded from http://jid.oxfordjournals.org/ at University of York on May 4, 2015
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 ~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.
1ID 1992; 166 (September)
Concise Communications
dates, the denominator contribution and any acute infection detected during that interval were attributed to the older age group. If two fourfoldantibody riseswere detected in immediate succession (three sequential specimens), a single infection was considered to have occurred. Therefore, serum sample intervals immediately following intervals in which acute infections were detected did not represent time at risk and were excluded from denominator calculations; however, subsequent serum sample intervals were included because> I acute infection per subject was considered possible(and did occur). Exact confidence limits for incidence rates were calculated from the Poisson distribution [7] except when no acute infections were observed, in which case the upper 95% confidence limit was calculated according to the method of Hanley and Lippman-Hand [8]. Infection rates were compared using a two-sided exact test for incidence density measures [9].
A total of 3671 serum specimens was tested from 343 subjects in 68 families; 64 infections were identified, 16 in adults and 48 in children. Fifty-eight persons had 64 infections, 4 had 2 infections, and I had 3. All but I with multiple infections were children. Infection with C. pneumoniae was detected in every year in which sera were collected, beginning in 1966. Of the 16 adult infections, 10 occurred in subjects with TW AR antibody in a preceding serum sample, suggesting reinfection. In only 4 adults was there a suggestion by prior serum samples without antibody that the infection was an initial one; in 2 adults it was not possible to ascertain prior infection because of the timing of serum collection. Of the adult infections, II were in men and 5 in women. Another indication of the difference in infection by sex in adults was the fact that throughout the period of observation 51 of 66 fathers of the families had antibody at any time compared with 40 of 68 mothers. Of the total of 48 infections in children, 39 appeared to be primary or first infections and 8 were reinfections; I could not be classified. Of the 8 reinfections, 5 were in 4 children who had had a primary infection during this study. Eight reinfections occurred at the same time other family members seroconverted, further confirming the significance ofTWAR antibody rises in persons with preexisting antibody. Analysis of the incidence of infection with C. pneumoniae was complicated by variability in the timing of serum collection. The use of data with long intervals between serum samples might result in failure to detect some acute infections or in misclassification of age or calendar time. During the FF study only 4% of the intervals between serum samples exceeded 6 months. Age-specific incidence rates of C. pneumoniae infection during 1975-1979 are shown in table I. Data from 37 acute antibody rises and 905 person-years of follow-up were used. The incidence of infection with C. pneumoniae was significantly higher for children 5-9 and
Table 1. Incidence of acute Chlamydia pneumoniae infection in Seattle, 1975-1979. Age (years)
No. of acute rises
Person-years
Incidence*
95% Cit
0-4 5-9 10-14 15-19 Adult Total
0 14 15 2 6 37
27 151 242 91 394 905
9.2 6.2 2.2 1.5
0, 11.1 5.1, 15.5 3.5,10.2 0.3,7.9 0.6,3.3
NOTE. Acute infection determined by fourfold antibody titer rises. Specimens collected after intervals ;;;.1 year excluded. * Rate/ I00 person-years at risk. t Exact 95% confidence interval (see Methods).
10-14 years old than for adults (P < .005, for each comparison). Incidence among 5- to 9-year-olds was also significantly higher than among 15- to 19-year-olds (P = .04). No significant differences in incidence were found between females and males among calendar years (1975-1979). The time intervals between serum specimens were too long and irregular before 1975 to allow calculation of meaningful incidence estimates. However, there were proportionately more data during 1966-1969 on very young children. During this time, I acute infection was detected in a boy whose serum IgG titer increased from 0 at birth to 16 at age 19 months. Serum from 2 family members collected the same day showed seroconversion since the collection of sera 6 months earlier. The decrease in antibody titer to C. pneumoniae during follow-up was examined among patients with fourfold antibody titer rises. Antibody patterns were characterized by comparing subsequent IgG titers to the highest titer after each acute rise. This was not always the first serum showing a fourfold rise since the titer in 9 subjects further increased in the next 1 or 2 serum specimens. Forty-one acute rises had follow-up data available for 8 months to 13 years (median, 32 months). During follow-up, the antibody level fell to
Seroepidemiology of Chlamydia pneumoniae TWAR Infection in Seattle Families, 1966-1979 Michael B. Aldous, J. Thomas Grayston, San-pin Wang, and Hjordis M. Foy
Departments ofEpidemiology and Pathobiology. University of Washington. Seattle
Chlamydia pneumoniae is a recently described third species in the genus Chlamydia that has been found to be a common cause of pneumonia and other respiratory infections in humans [I, 2]. Previous studies of C. pneumoniae, including most studies ofthe prevalence ofTWAR antibody, have used patient sera. Population incidence studies have not been done. This study has taken advantage of a unique serum bank from prospective family studies of respiratory infections conducted in the Seattle area during 1966-1979 by Fox et al. [3, 4]. Several prospective family studies of respiratory infections done before 1980 provide much of what we know ofthe epidemiology ofacute respiratory infections. Due to cost, however, it is unlikely that similar prospective studies will be done in the near future. This study provides information on the incidence of C. pneumoniae infection, the occurrence ofreinfection, and the transmission of the organism within families.
Methods Participants in the prospective family studies of respiratory infection were members of the Group Health Cooperative of Puget Sound. a large, prepaid health maintenance organization; participants were mostly white and middle class. Families in the Seattle Virus Watch (VW) study (1966-1969) were enrolled at the birth of a child [3]. Serum specimens were collected routinely twice per year and at times of illness. In 1972, 1973, and
Received 25 November 1992; revised 13 April 1992. Presented in part: 7th International Symposium on Human Chlamydial Infections. Harrison Hot Springs, Canada, June 1990. Grant support: National Institutes of Health (AI-21885). Reprints or correspondence: Dr. J. Thomas Grayston, Department of Epidemiology, SC-36, University of Washington, Seattle, WA 98195. The Journal of Infectious Diseases 1992;166:646-9 © 1992 by The University of Chicago. All rights reserved. 0022-1899/92/6603-0033$01.00
1974, members of some VW families gave yearly serum specimens for studies of influenza and Mycoplasma pneumoniae. The Seattle Family Flu (FF) study (1975-1979) included some of the original VW families and some new families; all had at least I child in elementary school [4]. Serum specimens were collected three times per year during this period. Stored sera from these studies were tested from two groups of families, those that participated in both the VW and FF studies and those that participated in only the FF study. Some members ofVW-FF families had specimens available from 1966 to 1979, except for 1970 and 1971. Intervals between successive serum specimens varied, especially between study periods; in addition, some specimens were missing or depleted. The proportions of specimens obtained from female and male subjects were approximately equal. For both groups, there were relatively few sera from children 60) are included. The median age was 39 years for male adults and 37 years for female adults.. Sera were tested for antibody in the immunoglobulin M and G (IgM and IgG) serum fractions using the microirnmunofluorescence technique [5] with TWAR antigen (strain AR-39) [6]. A fourfold rise in IgG titer between consecutive specimens was considered evidence ofacute infection. In other studies, a single IgM titer of ~ 16 or a single IgG titer of ~512 has been considered suggestive of acute infection. However, because the present study involved multiple serum collections unrelated to acute illness, this criterion was not used. Four persons had IgM antibody. In each, acute infection was independently demonstrated by fourfold rise in IgG titer. Of 8 specimens with an IgG titer of ~512, 6 were associated with antibody titer rises. The 2 other IgG titers of this magnitude were in subjects with sustained high antibody titers between 128 and 512, without a fourfold rise, and were not considered to indicate acute infection. Results of respiratory virus isolation and virus and mycoplasma serologic tests were available from the original studies [3, 4]. Denominators for incidence calculations were found by summing intervals between serum specimens within age groups. When a subject changed age groups between serum sample
Downloaded from http://jid.oxfordjournals.org/ at University of York on May 4, 2015
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 ~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.
1ID 1992; 166 (September)
Concise Communications
dates, the denominator contribution and any acute infection detected during that interval were attributed to the older age group. If two fourfoldantibody riseswere detected in immediate succession (three sequential specimens), a single infection was considered to have occurred. Therefore, serum sample intervals immediately following intervals in which acute infections were detected did not represent time at risk and were excluded from denominator calculations; however, subsequent serum sample intervals were included because> I acute infection per subject was considered possible(and did occur). Exact confidence limits for incidence rates were calculated from the Poisson distribution [7] except when no acute infections were observed, in which case the upper 95% confidence limit was calculated according to the method of Hanley and Lippman-Hand [8]. Infection rates were compared using a two-sided exact test for incidence density measures [9].
A total of 3671 serum specimens was tested from 343 subjects in 68 families; 64 infections were identified, 16 in adults and 48 in children. Fifty-eight persons had 64 infections, 4 had 2 infections, and I had 3. All but I with multiple infections were children. Infection with C. pneumoniae was detected in every year in which sera were collected, beginning in 1966. Of the 16 adult infections, 10 occurred in subjects with TW AR antibody in a preceding serum sample, suggesting reinfection. In only 4 adults was there a suggestion by prior serum samples without antibody that the infection was an initial one; in 2 adults it was not possible to ascertain prior infection because of the timing of serum collection. Of the adult infections, II were in men and 5 in women. Another indication of the difference in infection by sex in adults was the fact that throughout the period of observation 51 of 66 fathers of the families had antibody at any time compared with 40 of 68 mothers. Of the total of 48 infections in children, 39 appeared to be primary or first infections and 8 were reinfections; I could not be classified. Of the 8 reinfections, 5 were in 4 children who had had a primary infection during this study. Eight reinfections occurred at the same time other family members seroconverted, further confirming the significance ofTWAR antibody rises in persons with preexisting antibody. Analysis of the incidence of infection with C. pneumoniae was complicated by variability in the timing of serum collection. The use of data with long intervals between serum samples might result in failure to detect some acute infections or in misclassification of age or calendar time. During the FF study only 4% of the intervals between serum samples exceeded 6 months. Age-specific incidence rates of C. pneumoniae infection during 1975-1979 are shown in table I. Data from 37 acute antibody rises and 905 person-years of follow-up were used. The incidence of infection with C. pneumoniae was significantly higher for children 5-9 and
Table 1. Incidence of acute Chlamydia pneumoniae infection in Seattle, 1975-1979. Age (years)
No. of acute rises
Person-years
Incidence*
95% Cit
0-4 5-9 10-14 15-19 Adult Total
0 14 15 2 6 37
27 151 242 91 394 905
9.2 6.2 2.2 1.5
0, 11.1 5.1, 15.5 3.5,10.2 0.3,7.9 0.6,3.3
NOTE. Acute infection determined by fourfold antibody titer rises. Specimens collected after intervals ;;;.1 year excluded. * Rate/ I00 person-years at risk. t Exact 95% confidence interval (see Methods).
10-14 years old than for adults (P < .005, for each comparison). Incidence among 5- to 9-year-olds was also significantly higher than among 15- to 19-year-olds (P = .04). No significant differences in incidence were found between females and males among calendar years (1975-1979). The time intervals between serum specimens were too long and irregular before 1975 to allow calculation of meaningful incidence estimates. However, there were proportionately more data during 1966-1969 on very young children. During this time, I acute infection was detected in a boy whose serum IgG titer increased from 0 at birth to 16 at age 19 months. Serum from 2 family members collected the same day showed seroconversion since the collection of sera 6 months earlier. The decrease in antibody titer to C. pneumoniae during follow-up was examined among patients with fourfold antibody titer rises. Antibody patterns were characterized by comparing subsequent IgG titers to the highest titer after each acute rise. This was not always the first serum showing a fourfold rise since the titer in 9 subjects further increased in the next 1 or 2 serum specimens. Forty-one acute rises had follow-up data available for 8 months to 13 years (median, 32 months). During follow-up, the antibody level fell to
