Risk Factors for Chlamydia in Multi-ethnic Women
Risk Factors for Chlamydia in Multi-ethnic Women
The mean age of the 954 participants who returned repeat samples was 21.5 years (SD 2.9, range 16–27 years) and 26% (251) were of an ethnic minority background (black African n=94, black Caribbean n=74, black other n=12 and other ethnic groups n=71). In all, 77% (737/954) were recruited from universities and the remainder from FE colleges; 37% (352/954) were teenagers aged <20 years.
Table 1 shows that women who returned repeat postal specimens were similar to those who did not in the proportion who reported a new partner in the previous year and who were aged <16 years at first sex. However, they were slightly older, and less likely to be of black ethnicity or to have had chlamydia or bacterial vaginosis at baseline.
Among 907 women who were negative for chlamydia at baseline and followed up for 11–32 (median 16) months, the proportion with incident chlamydia infection was 4.6% (n=42, 95% CI 3.4% to 6.2%) (figure 1). Taking into account the total follow-up time (1234 person-years), the estimated annual incidence of infection was 3.4 per 100 person-years (95% CI 2.5 to 4.6 per 100 person-years). In participants aged <20 years, the proportion with incident infection was 8.9% (29/326, 95% CI 6.0% to 12.5%) and the annual rate was 6.6 per 100 person-years (95% CI 4.5 to 9.3 per 100 person-years). Predictors of incident chlamydia infection were age <20 years (RR 4.0, 95% CI 2.1 to 7.5), and (after adjusting for age) a new sexual partner during 12 months follow-up (RR 4.4, 95% CI 2.0 to 9.9), smoking (RR 2.2, 95% CI 1.2 to 3.9), baseline bacterial vaginosis (RR 2.0, 95% CI 1.1 to 3.9) and baseline high risk carcinogenic human papillomavirus (RR 2.2, 95% CI 1.1 to 4.3) (Table 2).
(Enlarge Image)
Figure 1.
Flowchart for 954 women who provided repeat postal samples 11–32 (median 16) months after recruitment.
Among the 954 women providing follow-up samples, 4.9% (n=47, 95% CI 3.6% to 6.5%) tested positive for chlamydia at recruitment and 5.7% (n=54, 95% CI 4.3% to 7.3%) were positive at follow-up. The proportion with redetected chlamydia among 47 women positive at recruitment was 25.5% (n=12, 95% CI 13.9% to 40.3%). Taking into account the total follow-up time of 65 person-years, the annual redetection rate was 18.5 per 100 person-years (95% CI 9.9 to 30.0 per 100 person-years). Chlamydia redetection was not significantly associated with any of the tested risk factors, but numbers were small (Table 3).
Among the 12 women with redetection of chlamydia infection, six had baseline and follow-up specimens with adequate DNA load for genetic typing. Four had the same omp1 genotype detected in both specimens suggesting treatment failure, reinfection from an untreated partner or reinfection from a new partner carrying the same genotype. Two, however, were probably infected from a new partner, as the genotype of the C. trachomatis strain had changed between the two time points.
Results
Participant Characteristics
The mean age of the 954 participants who returned repeat samples was 21.5 years (SD 2.9, range 16–27 years) and 26% (251) were of an ethnic minority background (black African n=94, black Caribbean n=74, black other n=12 and other ethnic groups n=71). In all, 77% (737/954) were recruited from universities and the remainder from FE colleges; 37% (352/954) were teenagers aged <20 years.
Table 1 shows that women who returned repeat postal specimens were similar to those who did not in the proportion who reported a new partner in the previous year and who were aged <16 years at first sex. However, they were slightly older, and less likely to be of black ethnicity or to have had chlamydia or bacterial vaginosis at baseline.
Incidence of Chlamydia Infection
Among 907 women who were negative for chlamydia at baseline and followed up for 11–32 (median 16) months, the proportion with incident chlamydia infection was 4.6% (n=42, 95% CI 3.4% to 6.2%) (figure 1). Taking into account the total follow-up time (1234 person-years), the estimated annual incidence of infection was 3.4 per 100 person-years (95% CI 2.5 to 4.6 per 100 person-years). In participants aged <20 years, the proportion with incident infection was 8.9% (29/326, 95% CI 6.0% to 12.5%) and the annual rate was 6.6 per 100 person-years (95% CI 4.5 to 9.3 per 100 person-years). Predictors of incident chlamydia infection were age <20 years (RR 4.0, 95% CI 2.1 to 7.5), and (after adjusting for age) a new sexual partner during 12 months follow-up (RR 4.4, 95% CI 2.0 to 9.9), smoking (RR 2.2, 95% CI 1.2 to 3.9), baseline bacterial vaginosis (RR 2.0, 95% CI 1.1 to 3.9) and baseline high risk carcinogenic human papillomavirus (RR 2.2, 95% CI 1.1 to 4.3) (Table 2).
(Enlarge Image)
Figure 1.
Flowchart for 954 women who provided repeat postal samples 11–32 (median 16) months after recruitment.
Redetection Rates of Chlamydia Infection
Among the 954 women providing follow-up samples, 4.9% (n=47, 95% CI 3.6% to 6.5%) tested positive for chlamydia at recruitment and 5.7% (n=54, 95% CI 4.3% to 7.3%) were positive at follow-up. The proportion with redetected chlamydia among 47 women positive at recruitment was 25.5% (n=12, 95% CI 13.9% to 40.3%). Taking into account the total follow-up time of 65 person-years, the annual redetection rate was 18.5 per 100 person-years (95% CI 9.9 to 30.0 per 100 person-years). Chlamydia redetection was not significantly associated with any of the tested risk factors, but numbers were small (Table 3).
Among the 12 women with redetection of chlamydia infection, six had baseline and follow-up specimens with adequate DNA load for genetic typing. Four had the same omp1 genotype detected in both specimens suggesting treatment failure, reinfection from an untreated partner or reinfection from a new partner carrying the same genotype. Two, however, were probably infected from a new partner, as the genotype of the C. trachomatis strain had changed between the two time points.
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