BMC Public Health 2009, 9:310 http://www.biomedcentral.com/1471-2458/9/310 sex than their counterparts at home). However, the pro- portion absent (which amounted to 11–14% among women overall) was rather low and thus is not likely to have caused a major bias. The modest effect of adjusting for proximate variables may be due to bias in the self- reporting of sexual behaviour as women have a tendency to underreport stigmatized sexual behaviour experiences and over-report normative behaviour [41,42]. A particular example in this regard was the revealed 4.1% HIV preva- lence among young urban women who reported never engaging in sexual intercourse. Since the epidemic in Zambia is mainly transmitted through heterosexual inter- course and the likelihood that women aged 15–24 in the pre-ARV era have survived with a HIV infection transmit- ted from the mother during pregnancy/infancy, is extremely low, this indicates a certain underreporting of sexual activity. Other studies have also discovered current pregnancy, HIV and sexually transmitted infections among young people who denied having sex [2,42,43]. Some of the young women who denied having had sex may have been raped or forced to have sex and denied sex- ual activity, as they had not participated voluntarily. A study in Kenya found that half the adolescent girls who claimed that they had never had sex, reported having been forced to have sex [44]. Ten percent of Zambian women aged 15–19 had been forced to have sex against their own will according to the Zambia Sexual Behaviour Survey 2005 [45]. Finally, a cross-sectional survey does not allow determination of whether exposure to neighbourhood factors precedes the development of the outcome. Conclusion In conclusion, the findings suggested neighbourhood contextual effects on HIV prevalence in these very HIV prevalence areas. Neighbourhood educational attainment appeared as a good proxy of the socioeconomic position and is likely to capture a complexity of overlapping con- textual factors. In this regard the strength of the local edu- cational system seems to be a case in point, supporting the value of ongoing efforts to improve access to secondary education particularly for women. However, more com- plex structural approaches will be needed to reduce HIV risk and vulnerability. Future research should include more neighbourhood factors of relevance to HIV preva- lence as part of the effort to better understand the causal mechanisms involved. Competing interests The authors declare that they have no competing interests. Authors' contributions NK participated in the analysis and interpretation of the data and led the drafting of the manuscript. IFS actively participated in interpreting the results as well as revising the manuscript. 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