Unadjusted and adjusted hazard ratios for incidence of chlamydial infection among 16–24-year-old women by setting of recruitment and population characteristics, England, March 2002–August 2003
| Characteristic | Recruited from general practice | Recruited from family planning | Recruited from GUM | Total stratified by healthcare setting of recruitment |
|---|---|---|---|---|
| Unadjusted hazard ratios (95% CI) | Unadjusted hazard ratios (95% CI) | Unadjusted hazard ratios (95% CI) | Adjusted hazard ratios* (95% CI) | |
| Total | Ref. | 1.3 (0.6 to 2.7)p = 0.497 | 2.1 (1.1 to 4.3)p = 0.032 | |
| GUM, genitourinary medicine; ref, reference group. | ||||
| *Adjusted hazard ratios come from a multivariable Cox regression stratified by healthcare setting of recruitment. | ||||
| †Variable selection in adjusted stratified Cox regression model was influenced by unadjusted hazard ratios (p<0.10) and epidemiological factors previously found to be associated with incidence. | ||||
| ‡Last adjusted hazard ratio before the variable was dropped from multivariable modelling. | ||||
| §The rate of new sexual partner change for the time period immediately preceding infection. | ||||
| ¶Rate of new sexual partner change as continuous. | ||||
| **Rate of new sexual partner as a continuous variable was not included in the final adjusted multivariable model as the categorical variable was determined to be more explanatory. | ||||
| No evidence found for non-proportional hazards in the final adjusted multivariable model (p = 0.66). No evidence of a difference between healthcare settings of recruitment (in a model with healthcare setting of recruitment as a covariate rather than as a stratification variable; p = 0.61). | ||||
| Reason for attendance (baseline) | ||||
| Attended for symptoms | No events | 2.1 (0.6 to 7.3)p = 0.237 | 1.1 (0.5 to 2.5)p = 0.878 | |
| Other reason, but reported symptoms | 1.9 (0.6 to 6.4)p = 0.272 | 0.4 (0.1 to 1.5)p = 0.192 | 1.2 (0.5 to 3.0)p = 0.663 | |
| Asymptomatic | Ref | Ref | Ref | |
| Age group (years)† | ||||
| 16–17 | 2.7 (0.7 to 10.7)p = 0.162 | 1.4 (0.5 to 3.7)p = 0.534 | 1.4 (0.5 to 4.1)p = 0.503 | 3.1 (1.3 to 7.4)p = 0.013 |
| 18–20 | 0.7 (0.2 to 3.3)p = 0.692 | 0.5 (0.2 to 1.7)p = 0.294 | 1.9 (0.8 to 4.2)p = 0.137 | 1.1 (0.5 to 2.8)p = 0.763 |
| 21–24 | Ref | Ref | Ref | Ref |
| Ethnic group† | ||||
| White | Ref | Ref | Ref | Ref |
| Non-white | No events | No events | 11.2 (2.6 to 48.7)p = 0.001 | 7.8 (1.6 to 39.4)p = 0.012 |
| Unknown | 1.2 (0.3 to 4.5)p = 0.787 | 0.3 (0.03 to 1.9)p = 0.185 | 0.9 (0.4 to 2.1)p = 0.761 | Not in model |
| Ever had chlamydia (baseline)† | ||||
| Yes | 2.0 (0.2 to 16.4)p = 0.514 | No events | 3.4 (1.6 to 7.6)p = 0.002 | 2.5 (1.1 to 6.1)p = 0.038 |
| No | Ref | Ref | Ref | Ref |
| Condom use at last sexual intercourse† | ||||
| Yes | 0.4 (0.1 to 3.6)p = 0.451 | 0.6 (0.2 to 2.2)p = 0.444 | 0.2 (0.03 to 1.8)p = 0.167 | 0.4 (0.2 to 1.2)p = 0.685‡ |
| No | Ref | Ref | Ref | Ref |
| Symptoms (yes, past 6 months) | No is ref | No is ref | No is ref | No is ref |
| Cystitis (urinary tract infection) | No events | 1.3 (0.4 to 4.7)p = 0.659 | 0.9 (0.3 to 3.2)p = 0.828 | |
| Frequent urination† | No events | 2.4 (0.8 to 7.7)p = 0.125 | 2.2 (0.7 to 6.7)p = 0.184 | 1.4 (0.5 to 3.7)p = 0.484‡ |
| Abdominal pain | 2.2 (0.5 to 8.7)p = 0.277 | No events | 0.9 (0.3 to 3.2)p = 0.895 | |
| Bleeding between periods | 1.8 (0.4 to 8.9)p = 0.446 | 0.5 (0.1 to 3.6)p = 0.474 | 1.5 (0.4 to 5.3)p = 0.521 | |
| Bleeding after sexual intercourse† | No events | 1.0 (0.1 to 7.6)p = 0.994 | 3.0 (0.9 to 10.6)p = 0.084 | 2.3 (0.7 to 7.4)p = 0.170‡ |
| Pain during sexual intercourse† | No events | 0.6 (0.1 to 4.3)p = 0.575 | 0.3 (0.04 to 2.6)p = 0.295 | 0.2 (0.03 to 1.6)p = 0.133‡ |
| Discharge† | 1.6 (0.3 to 7.8)p = 0.551 | 1.9 (0.5 to 6.6)p = 0.337 | 1.2 (0.3 to 4.2)p = 0.780 | 1.1 (0.3 to 3.2)p = 0.918‡ |
| None | 0.5 (0.1 to 2.2)p = 0.385 | 0.8 (0.3 to 2.1)p = 0.618 | 0.6 (0.2 to 1.7)p = 0.349 | |
| Recent rate of sexual partner change per 6 months†,§ | 10.1 (0.7 to 141)p = 0.087¶ | 2.2 (1.3 to 3.7)p = 0.003¶ | 1.7 (0.6 to 4.7)p = 0.270¶ | ** |
| No male sexual partner change | Ref | Ref | Ref | Ref |
| 1–3 new male sexual partners | 3.1 (0.8 to 12.3)p = 0.113 | 5.5 (1.5 to 20.3)p = 0.011 | 4.6 (1.5 to 14.1)p = 0.007 | 5.5 (2.2 to 13.9)p = 0.00‡ |
| >3 new male sexual partners | 27.7 (2.9 to 269)p = 0.004 | 98.1 (21.7 to 444)p = 0.00 | No events | 12.4 (2.8 to 54.2)p = 0.001‡ |
| Partner change and condom at last sexual intercourse | ||||
| Used a condom at last sexual intercourse, and: | ||||
| No male sexual partner change | Ref | Ref | Ref | Ref |
| 1–3 new male sexual partners | No events | 1.0 (0.1 to 11.3)p = 0.990 | 1.1 (0.1 to 9.8)p = 1.00 | 1.1 (0.2 to 6.7)p = 0.925 |
| >3 new male sexual partners | No events | No events | No events | No events |
| Did not use a condom at last sexual intercourse, and: | ||||
| No male sexual partner change | 0.8 (0.1 to 7.6)p = 0.838 | 0.2 (0.02 to 2.2)p = 0.186 | 1.7 (0.2 to 15.3)p = 0.630 | 0.7 (0.2 to 3.1)p = 0.685 |
| 1–3 new male sexual partners | 3.3 (0.4 to 29.7)p = 0.285 | 2.8 (0.6 to 13.1)p = 0.195 | 8.1 (1.1 to 62.3)p = 0.043 | 4.1 (1.1 to 14.5)p = 0.030 |
| >3 new male sexual partners | 85.8 (4.0 to 1831)p = 0.004 | 45.7 (8.3 to 253)p = 0.001 | No events | 9.2 (1.6 to 52.0)p = 0.012 |