The interviewers reported that the overall quality of the interview was either generally reliable (75.8%) or of high quality (22.2%). However, as shown in Figure , we observed a tendency for women to respond with preferences for terminal digits, e.g., of '0' or '5' when reporting their age. To verify the accuracy of our most important age analyses, we analyzed HR-HPV prevalence by using the standard IARC age categories [17
] and by a more agnostic age stratification in which women were grouped according to the midpoint between digit preferences. Using these two different age categories, we found slightly different HR-HPV prevalence curves among younger women (Figure ). We attribute this difference to the high HR-HPV prevalence among women aged 25 years (36%). In contrast, the curve appeared similar among older women.
Figure 1 Top: Graph showing preference for terminal digits 0 and 5 for self-reported age. Bottom: Percentage of women with high-risk human papillomavirus (HR-HPV) shown using two different strategies for categorizing age. Abbreviations: IARC, International Agency (more ...)
Table summarizes the clinical questionnaire data and shows the relationship between these risk factors and HR-HPV positivity. In terms of menstrual history, most women (70%) reported age of menarche to be between 15-19 years (average age 16.1 ± 2.5 years). The majority of women reported an average age at sexual debut of 20 years. Most women reported only one sex partner in the last two years (~80%). The average age of first pregnancy was 23.1 years and about 50% of women reported having between 5-9 lifetime pregnancies (average number 6.5 ± 3.2 pregnancies). Only a small percentage of women reported using birth control (14%) and of those women very few responded as to what type, although hormonal contraception appeared to be the predominant method in comparison to condom use (data not shown).
Clinical questionnaire responses and potential risk factors for high risk human papillomavirus positivity
In terms of marital status and related variables, the majority of women were in union (either married or living with a man) and about 60% of these women reported that they resided in a household with co-wives, reflecting the over-sampling in our field effort. A relatively equal percentage reported having 1, 2, or 3+ co-wives and 45% stated that they were ranked first among other wives. This reflects that our recruitment efforts were particularly successful among older women. The average age of the youngest wife was 39.4 ± 10.7 years.
Most women reported that neither they nor their husbands used tobacco, thus the overall exposure to tobacco was relatively low (15.2%). A majority of women reported having at least one case of malaria in the past two years (average number of diagnoses 2.2 ± 1.5).
Overall, age was observed to be a risk factor, although a non-linear one, for presence of HR-HPV, as we observed an increased prevalence in women 15-29 (18.9%) and 56+ years (15.1%). An age of 10-14 years at sexual debut was associated with a nearly two and a half-fold risk for HR-HPV infection (OR 2.4; 95% CI 1.1-5.3) compared to late age. Early rather than late age of first pregnancy was also associated with increased HR-HPV prevalence with a 40% increased risk for ages 12-19 (OR 1.4; 95% CI 0.9-2.4) and a 50% increased risk for ages 20-24 years (OR 1.5; 95% CI 1.1-2.2) compared to late age. Having more than two sexual partners and use of birth control were also positively related to HR-HPV risk (OR 1.4; p-value = 0.07 and OR 1.6; p-value = 0.03).
With regard to our more novel hypothesized risk factors, we did not find associations of interest. Living in a household with co-wives was associated with a slightly decreased risk of HR-HPV positivity (OR 0.8; p-value = 0.24) although this relationship was not significant. The number of self-reported malaria diagnoses in the past two years was not associated with increased risk of HR-HPV prevalence (p-value = 0.85).
Table shows the distribution of key questionnaire variables determined by the analyses above, including those that we felt to be important risk factors to explore, stratified by age. Women 15-29 years reported younger ages at sexual debut and first pregnancy while women 50+ years recalled the highest ages for these measures. In addition, younger women were more likely to have greater than two sex partners in comparison to women aged 45-55 and 56+ years. The number of women using birth control was highest among the 46-55 year olds and lowest in women aged 56+ years. Women 30 years or older were the most likely to be in a household with co-wives, while most women aged 15-29 years did not live in a household with co-wives. Interestingly, self-reported malaria was most prevalent in women aged 56+ years, who were more likely to report three or more cases in the past 2 years and lowest among women 15-29 years of age, who frequently reported one or fewer cases.
Key clinical questionnaire responses stratified by age
Table shows the risk of HR-HPV infection for table variables within age strata. We had hypothesized that the risk factors might help explain the high HR-HPV prevalence at older ages. However, age stratification did not reveal strong and consistent explanatory differences. The slight differences are as follows: An age of 10-14 years at sexual debut was associated with a five-fold risk for HR-HPV (10-14 years: OR 5.0; 15-24 years: OR 1.2; p-trend = 0.02) in women aged 30-45 years. Early age at first pregnancy was associated with a greater than two-fold risk for HR-HPV in women aged 56+ years (12-19 years: OR 2.4; 20-24 years: OR 2.2; p-trend = 0.04). Early age at sexual debut was also a risk factor among women in this age group, although the association was not quite as strong (15-24 years: OR 1.6; p-value = 0.15). Multiple sex partners and birth control use were risk factors for women aged 30-45 (OR 1.7; p-value = 0.08 and OR 1.8; p-value = 0.8, respectively). Living in a household with co-wives was not associated with HR-HPV in this age stratified analysis. We did observe somewhat of a dose response relationship with the number of recent self-reported malaria diagnoses and HR-HPV prevalence in women aged 15-29 years, although this relationship was not significant (p-trend = 0.31).
Risk factors for high risk human papillomavirus positivity stratified by age