Ziraba et al. BMC Public Health 2011, 11:663 http://www.biomedcentral.com/1471-2458/11/663 the various dimensions of HIV/AIDS-related stigma. The HIV-testing status was taken with no time boundaries (ever tested) and yet individual’s HIV status can change in a matter of weeks. At the time of designing the study, it was envisaged that few people had ever tested and even fewer would have been tested in the last one year. Besides, from a program point of view, it can be argued that knowledge of a test result is likely to have a relatively long-term impact on behaviour probably stretching beyond the commonly arbitrarily set cut-off of one year. Lastly, there was potential selection bias given that a sub- stantial proportion of the sample initially targeted did not participate in the study. However an assessment of potential bias in the HIV prevalence estimates due to non-participation showed that selection bias was unlikely because overall HIV prevalence was overestimated by only 2% (overestimated by 3% among women and under- estimated by 1% among males) [39]. Conclusions The proportion of individuals who have ever had testing and counselling in the two informal settlements is lower- (62% for women and 38% for men) than that of Nairobi as a whole (76% for women and 60% for men), but more comparable to the national average (58.4% for women and 42% for men) over the period 2003-2008 [10]. The unmet need for testing and counselling is high and, therefore, programs should intensify their efforts to reach out to this sub-population. The main determinants for HIV counsel- ling and testing were; gender, age, marital status, ethnicity, and favourable attitude towards knowing one’s status. Other less strongly associated factors include HIV related knowledge and HIV/AIDS-related stigma. Our results further showed that the determinants for PITC and CITC are not exactly the same. For example, while secondary or higher education; and positive or unknown status were associated with higher tendency to use CITC, these factors did not matter for PITC. Also, while individuals with the most stigmatising tendency were less likely to have had CITC, levels of one’s stigma did not influence use of PITC. These differences may need to put into considera- tion while trying to promote up take of testing and coun- selling. Provider-initiated testing and counselling constitutes a sizeable proportion of all those tested and seems to be helping to increase overall testing rates and should be promoted more in the future. Acknowledgements We extend our sincere thanks to Viwandani and Korogocho communities for their continued support and participation in our research projects. The project from which data used in this paper are derived benefited from the generous financial support from the Rockefeller Foundation under grant 2006AR013 and financial support to NUHDSS from The Wellcome Trust grant-GR078530MA, and Hewlett Foundation grant-2006-8376. Page 9 of 10 Author details 1African Population and Health Research Center, Kirawa Road, off Peponi Road P. O. Box 10787, 00100, Nairobi, Kenya. 2Faculty of Epidemiology and Population Health, Department of Population Studies. London School of Hygiene and Tropical Medicine. Room LG21, Keppel Street, London, WC1E 7HT, UK. 3University of Southampton, School of Social Sciences, SO17 1BJ, Southampton, UK. 4Kenya Medical Research Institute (KEMRI). P. O. Box 54840, 00200, Nairobi, Kenya. Authors’ contributions AKZ took lead in preparing the manuscript. He participated in designing, implementing, data management and analysis and manuscript writing. NM participated in proposal development, study design, project implementation, supervision and manuscript preparation. JKK participated in data analysis and manuscript preparation. MM participated in the proposal development, study design, project implementation, supervision of blood sample testing and manuscript preparation. SO participated in writing of the background section, interpretation of results and writing of the discussion section. GM participated in writing the methods and discussion sections and provided overall support for the manuscript preparation. AE participated in the proposal development, study design, project implementation, supervision and overall project management. He also participated in manuscript preparation. All authors read and approved the final manuscript. Conflicts of interests The authors declare that they have no competing interests. Received: 29 January 2011 Accepted: 23 August 2011 Published: 23 August 2011 References 1. 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