Determinants of sexual activity
The median age of sexual debut was 17 years and the median number of lifetime sexual partners was 2 for cases and controls. As can be seen in Table 1 showing a comparison of socio-demographic background of cases and controls, women in both groups had similar characteristics: the mean age was 45 and 44 years respectively; urban residence 58% and 54% and having more 5 or more years of schooling, 76% and 72% respectively; the proportion of married women was 46% and 51% respectively and black and coloured women both 25% and 75% respectively.
Distributions of age of sexual debut and number of sexual partners were similar across major diagnostic categories (trauma, acute infection, other conditions) among controls.
Both tables 2 and 3 show socio-economic factors associated with earlier sexual debut and increased number of partners respectively. These are restricted to controls.
Age at sexual debut
Twenty-three percent of the controls had sex < 16 years. The chi square test for trend, an indicator of changes over time, was 1.33, p = 0.25, showing no evidence of a trend of younger sexual debut over time. Table 2 describes socio-demographic factors associated with earlier age at first intercourse and gives crude and adjusted prevalence ratios (APR) for age at first sexual intercourse < 16 years relative to first sex at age ≥ 17 among the controls.
The strongest risk association was for < 4 years of education, (APR = 4.1, 95% CI 2.6–6.6) relative to ≥ 10 years. Other factors significantly associated with age of sexual debut < 16 years, were ≥ 4 sexual partners relative to 1 (APR 1.9, 95% CI 1.3–2.7) and current alcohol use relative to nonuse (APR = 1.4, 95% CI 1.1–1.8); and Age, marital status, race, residence, ever-use of hormonal contraceptives, ever had a Pap smear, smoking status and having current high risk HPV were not significantly associated with early sexual debut. As there was very little reported condom use, few women had knowledge of whether reproductive infections they had had were STI's or not and few women knew whether their partners had had an STI, this had little impact on the analysis.
Number of sexual partners
Thirty-nine percent of controls had had at least three sexual partners. Table 3 describes socio-demographic factors associated with an increased number of sexual partners, ≥ 3, relative to 1 partner for among the controls.
Having had ≥ 3 partners was strongly associated with commencement of sexual debut at a younger age (< 16: APR= 2.4, 95% CI 1.8–3.4; 16–19 years: APR= 2.1, 95% CI 1.6–2.9) and being black, (APR = 1.9, 95% CI 1.5–2.3). Other significantly associated factors included being single (APR, 1.3), higher educational levels (APR's for both 5–9 years and ≥ 10 years, 1.3) and current or past alcohol use (APR's 1.6 and 1.7 respectively). Having had ≥ 3 sexual partners was not significantly associated with age, residence, ever-use of hormonal contraceptives, smoking status, having had a Pap smear and having current high risk HPV.
Sexual activity and cervical cancer risk
Table 4 shows cervical cancer risk, as crude and adjusted odds ratios, in relation to the age at first sexual intercourse.
Relative to those who commenced sexual intercourse at age ≥ 20 years, the multivariate adjusted odds ratio for age at commencement at age < 16 years was 1.6 (95% CI, 1.2–2.2) (p = 0.0006); among coloured and black women the estimates were 1.7 (95 % CI, 1.2–2.4) (p = 0.002) and 1.3 (95% CI 0.7–2.4) respectively.
Table 5 shows cervical cancer risk, as crude and adjusted odds ratios, in relation to the number of lifetime partners.
The multivariate adjusted OR increased with increasing number of sexual partners, to 1.7 (95% CI, 1.2 – 2.2) (p = 0.0001) for ≥ 4 lifetime sexual partners relative to 1. The adjusted OR for cervical cancer in women who had ≥ 4 lifetime sexual partners was 2.0 (95% CI 1.4–2.9) (p < 0.0001) among coloured women and 1.2 (95% CI, 0.6–2.3) among black women. When high risk HPV positive controls only were included (16% of the women), the results were unchanged.