These data and analyses demonstrate a novel use of ANC surveillance data to reveal changes in HIV infection risk associated with marital history in a rural African community at a time when HIV prevalence is stable and may be starting to decline. Inclusion of marital history questions did not appear to affect participation rates adversely (<1% refusals), although some women may have avoided clinics during recruitment periods. The study design did not allow assessment of the impact of different types of questioning on participation rates.
The data show no evidence of continued risk of HIV acquisition for women below 25 years of age in first marriages, but that extended pre-marital exposure, subsequent extra-marital exposure or exposure during subsequent marriages are all associated with increased risk. This is consistent with findings in urban Kenya and Zambia that less than half of HIV in young married women is acquired within the marriage[12
] although analyses of those data concluded that early marriage puts young women at higher risk than intermittent contact associated with pre-marital sex[13
]. Studies which found that never married women have lower HIV prevalence than married age-mates may not discriminate between virgins and sexually active single women[14
The lack of ongoing risk in first marriage may be in part an artefact of the cross-sectional study design as introduction of HIV over time may result in sub-fertility or mortality, removing individuals from the sample. However, it is also consistent with the relative sexual exclusivity of a stable first marriage: unfaithfulness, domestic violence associated with alcohol use and other factors associated with HIV risk also precipitate marital break-up.
The insights these data give into sexual behaviour and associated risk of HIV demonstrate the usefulness of simple interviews during ANC surveillance. As with all ANC based surveillance, results are only generalisable to women who conceive. AIDS is likely to be responsible for much of the widowhood in women under 25, thereby lowering conception risks for women with a high probability of being infected. Relative age of current sexual partner, use of contraception and low parity for age are also associated with increased risk. Other community based data from this project reveal that although more than 99% of women attend antenatal clinic when carrying an established pregnancy, approximately one third of all women of childbearing age have not attended ANC in the four years prior to being surveyed[15
]. Nearly 90% of the ANC non-attenders have never had a child (the remainder having unusually long birth intervals), and although a third of these are virgins, there are many women with low fertility or whose lifestyles preclude stable relationships and childbearing, who are at relatively high risk of HIV and need to be studied independently[10
There are data quality limitations for marital history and pre-marital sex questions in ANC interviews, and selective reporting of behaviour favoured by health education messages may be common in this setting. Health education intensifies over time and younger women may feel less inclined to report actual rather than “acceptable” behaviour (e.g. reporting informal relationships resulting in pregnancy as “marriage”). The lack of a question on the date first marriage ended made it necessary to impute time spent in and after the terminated first marriage in divorcees or widows. However, given those caveats, this study presents clear and plausible findings on recent behaviour amongst young, sexually active women in this community.
These data show a downward trend of HIV prevalence over time in women under 25, which remains significant when other factors are controlled. The introduction of PMTCT to the district did not influence this trend as a real effect nor artefactually, as introduction was low key and piece-meal, and data-collection was not conducted in any clinics with established PMTCT services. We looked at two ways of quantifying this trend: first, looking at change in the odds ratio of infection in relation to calendar year of interview; second, looking at the effect of the women's birth cohort (year of birth). The fact that the latter exerts a stronger effect suggests that younger birth cohorts adopt safer sexual behaviour more quickly, even after allowing for their reduced length of exposure to marital and extra-marital sex.
The unmeasured favourable behaviour change could be fewer sexual partners, less frequent contacts with high risk partners, or increased condom use. Direct questions on these behaviours were introduced only in the latter part of the study; thus insufficient data have been collected to allow for a more complete analysis. Although these questions were completed, interviewers reported an element of reluctance or concealment in answering these direct enquiries as indeed there may have been when reporting age at first sex, although this was not pronounced.
The difficulty in elucidating reliable responses to specific sexual behaviour questions in this high through-put clinical setting, emphasises the value of informative but less controversial questions such as marital history and age at sexual debut, which may be less prone to social desirability biases, and easier to check. Quality of data particularly on the latter question will be improved with appropriate training of interviewers in language and attitudes, by ensuring privacy during interviews and by emphasising confidentiality and anonymity to the client.
In this population, pre-marital sex is the norm and pregnancy is a common precipitant for marriage[17
]. This is reflected in the contribution of up to 10 years of pre-marital sexual exposure in the group studied, carrying a year-on-year risk of HIV which was as high as exposure of women in vulnerable inter- or post- marriage periods of their lives. Pre-marital sex for teenage girls may occur with age-mates (eg school friends) or with older men. In the teenage women sampled here (who may or may not have been married by the time of presentation at ANC), 40% of pregnancies were reported to be by a man from an age cohort at least 5 years above hers. The corresponding figure is 29% for women in their early twenties.
Qualitative work in this population suggests that women of 16 years or under have pre-marital sex only on isolated occasions: unexpected and irregular (and consequently, unprotected) [17
]. Women in their twenties are more likely to have had regular boyfriends prior to marriage.
Although there appears to have been a decline in HIV prevalence between the first three and last three years of this study, the significance of this overall trend cannot be inferred directly as ANC surveillance was not continuous in all participating clinics. Areas of residence differ in their HIV infection prevalences, and some were not represented in the latter years.
The association of HIV with low parity for age may be causal in either direction: long-standing HIV infection is a biological cause of infertility and a social cause of infertility (due to widowhood), and other sexually transmitted infections increase the risk of both infertility and HIV acquisition. Primary or secondary infertility can destabilise marriage [14
] and lead to periods of risky exposure. The association of HIV with low parity in this young age group was not significant, when adjusted for other factors.
We have shown that it is possible to collect useful data on sexual behaviour in an ANC setting. Questions on age at first sex may answered less well in older than in younger women, but it is the age at sexual debut in the youngest groups which give cogent information on trends, and the questions are generally well-answered in this group. The same data collection tools, with the addition of dates of termination of marriages to avoid the need for imputation, can be used in PMTCT settings to investigate whether women who choose to attend one facility in preference to another have different behavioural characteristics, which may explain any observed HIV prevalence differences by facility type. The Malawi National AIDS Commission used a variant of marital status questions developed at KPS in their last round of ANC surveillance, and it is to be hoped that other ANC surveillance programmes will follow suit, with appropriate quality controls in place.