Table 1

Characteristics of the study population by chlamydia status at start of NECCST

Overall
n (%)
Chlamydia negative
n (%)
Chlamydia positive
n (%)
P value
5704 (100%)4022 (70.5%)1682 (29.5%)
Age (years) mean (SD)31.1 (3.8)31.2 (3.8)30.9 (3.8)0.003*
Chlamydia positivity in CSI-PCR n (%)908 (15.9)908 (54.0)
Gonorrhoea positivity n (%)112 (2.0)32 (0.8)80 (4.8)<0.001*
Migration background<0.001*
 Western4565 (80.0)3382 (84.1)1183 (70.3)
 Non-Western869 (15.2)464 (11.5)405 (24.1)
 Unknown270 (4.7)176 (4.4)94 (5.6)
Educational level†‡<0.001*
 Low/middle1170 (20.5)661 (16.5)509 (30.3)
 High4529 (79.5)3358 (83.6)1171 (69.7)
Age at sexual debut mean (SD)16.9 (2.4)17.2 (2.4)16.4 (2.1)<0.001*
Lifetime sex partners<0.001*
 <61797 (31.5)1.499 (37.3)298 (17.7)
 6–122033 (35.6)1424 (35.4)609 (36.2)
 >121874 (32.9)1099 (27.3)775 (46.1)
Condom use with casual partners§<0.001*
 Never/not often340 (6.0)243 (6.1)97 (5.8)
 Sometimes1807 (31.7)1100 (27.4)707 (42.1)
 Always/mostly2579 (45.9)1890 (47.1)720 (42.9)
 No casual partners936 (16.4)780 (19.4)156 (9.3)
Use of IUD0.230
 Never3672 (64.4)2609 (64.9)1063 (63.2)
 At least once2032 (35.6)1413 (35.1)619 (36.8)
Smoking<0.001*
 Never2264 (39.7)1724 (42.9)540 (32.1)
 Sometimes/in the past2843 (49.8)1960 (48.7)883 (52.5)
 Daily597 (10.5)338 (8.4)259 (15.4)
No of chlamydia tests<0.001*
 11042 (18.3)931 (23.2)111 (6.6)
 21539 (27.0)1222 (30.4)317 (18.9)
 31485 (26.0)1032 (25.7)453 (26.9)
 >31638 (28.7)837 (20.8)801 (47.6)
Chlamydia symptoms¶
 No952 (56.6)
 Yes730 (43.4)
No of chlamydia infections**
 11325 (78.8)
 2291 (17.3)
 3 or more66 (3.9)
Age at first chlamydia infection
 <20305 (20.8)
 20–24640 (43.7)
 >24519 (35.5)
Chlamydia IgG antibodies (serology)
 No3101 (54.4)2572 (64.0)529 (31.5)
 Yes569 (10.0)569 (33.8)
 Unknown2034 (35.7)1450 (36.0)584 (34.7)
  • Chlamydia positive was defined as a positive PCR-test outcome in the CSI study (CSI-PCR), and/or the presence of chlamydia IgG and/or a self-reported chlamydia infection.

  • *Statistically significant, p<0.05.

  • †Educational level: low/medium level of education: no education, primary education only, lower general secondary education and vocational education; high level of education: all other education levels. Chlamydia symptoms were vaginal discharge, abdominal pain or pain during intercourse and/or intermittent vaginal bleeding.

  • ‡At start of NECCST and based on 5699 observations, 5 missing.

  • §Based on 5693 observations, 11 missing.

  • ¶based on 1665 observations, 15 missing values.

  • **Based on 1639 observations, 43 missing.

  • CSI, Chlamydia Screening Implementation; IUD, intrauterine device; NECCST, Netherlands Chlamydia Cohort Study.