Younger women, white women and those with a single BNA or mild smear were less likely to provide an HPV sample than older women (χ32=8.30, P=0.040), non-white ethnic groups (χ12=8.19, P=0.004) or those with a previous abnormal smear (χ52=100.85, P<0.001). Since two of three centres did not take swabs from menstruating women, the proportion providing a sample varied by centre (χ22=294.53, P<0.001). It did not vary by tertiary education level (χ12=0.34, P=0.559).
The crude hrHPV prevalence was 39.2% (95% confidence interval (CI) 37.8–40.5). Positivity declined with increasing age (20–24 years 61.0%, 25–29 years 50.1%, 30–34 years 39.6%, 35–39 years 30.6%, 40–44 years 22.0%, 45–49 years 17.1% and 50–59 years 14–15%), and increased with increasing smear grade. For all grades, prevalence and risk were higher in younger (20–29 years) than older (
30 years) women, but not by a constant amount (; P
(interaction) 0.0004). The overall age-standardised prevalence was 34.2% (95% CI 32.6–35.8). For women with a current normal smear, it was 15.1% (95% CI 12.6–17.6), for those with a current BNA smear 30.7% (95% CI 8.6–32.8) and with a current mild smear 52.7% (95% CI 48.6–56.8).
Figure 1 hr HPV positivity (%) by smear status and age. BNA, smear showing BNA; mild, smear showing mild dyskaryosis; worse than mild, smear showing moderate or severe dyskaryosis; single BNA, women with a current BNA smear and no other BNA smear in previous (more ...)
Other factors significantly associated with hrHPV status in multivariate analyses were tertiary education level, ethnic group, marital status, reproductive history, hormonal contraceptive use and smoking (). Women with a college/university degree were at reduced hrHPV+ve risk compared with those without a degree. Although prevalence varied little by ethnic group, in multivariate analyses, non-white women (e.g. black-African, Indian, Pakistani) were at significantly increased risk. Single, and divorced/separated/widowed, women had significantly higher infection risk than married/co-habiting women. High-risk HPV infection was associated with never being pregnant, having had children and age at first pregnancy, but not with number of children or caesarean delivery. Combining pregnancy, childbirth and age at first pregnancy (as ‘reproductive history'), having a pregnancy resulting in childbirth was associated with lower infection risk, particularly for a first pregnancy at age
20 years. Current and previous oral contraceptive (OC) use (combined or progesterone-only), and current use of other hormonal contraception (e.g. implants, injections, intrauterine system), were associated with increased risk. Compared with never smokers, current smokers (but not ex-smokers) were at a modest increased risk, unrelated to smoking pack-years (data not shown). Barrier contraception and physical activity were also unrelated to risk.
Numbers and proportions of women hrHPV+ve and adjusted multivariate ORs for socio-demographic and lifestyle factors
In multivariate age-stratified analyses of women aged 20–29 years, age and smear status were significantly associated with infection. Tertiary education and having had children were also significant risk factors, with risk estimates similar to those in unstratified analyses. In women aged 30–59 years, age and smear status were significantly associated with infection, as were tertiary education, having had children, ethnicity and smoking; effect sizes were similar to those in . Other significant factors were marital status (increased risk in divorced/separated/widowed women (odds ratio (OR) 2.23, 95% CI 1.79–2.79) and single women (OR 1.84, 95% CI 1.35–2.50)), current hormonal contraceptive use (OR user vs non-user 1.30, 95% CI 1.03–1.64) and physical activity (OR active vs not active 0.76, 95% CI 0.60–0.97).
In multivariate smear-stratified analyses of all smear groups, age was significantly associated with infection. Having a college/university degree reduced infection risk in women with a current normal (OR 0.58, 95% CI 0.34–0.99) or BNA smear (OR 0.72, 95% CI 0.56–0.91) but not in those with a mild smear. In all smear strata, divorced/separated/widowed women had higher risk than married/co-habiting women (normal OR 1.64, 95% CI 0.91–2.96; BNA OR 2.26, 95% CI 1.73–2.95; mild OR 2.12, 95% CI 1.49–3.02). In the BNA strata only, being single also increased risk (OR 1.34, 95% CI 1.06–1.70). Having been pregnant was inversely associated with infection in those with a current normal (OR 0.60, 95% CI 0.38–0.95) or BNA smear (OR 0.81, 95% CI 0.64–1.02), but not in those with a mild smear. Having had children was associated with reduced risk in all smear strata, only reaching statistical significance in the current normal group (OR 0.57, 95% CI 0.36–0.92). Hormonal contraceptive use was associated with increased risk in the current normal (OR 1.59, 95% CI 1.02–2.48) and BNA (OR 1.29, 95% CI 1.05–1.59) strata, but not among the mild group. Barrier contraceptive use, caesarean delivery, smoking, physical activity and ethnicity were unrelated to infection in all strata.