African Journal of AIDS Research 2006, 5(3): 281–288 Printed in South Africa — All rights reserved Copyright © NISC Pty Ltd AJAR ISSN 1608–5906 Incidence of HIV-1 infection and changes in prevalence of reproductive tract infections and sexual risk behaviours: a population-based longitudinal study in rural Tanzania Elia J Mmbaga 1, 2 *, Akhtar Hussain 1 , Germana H Leyna 2,3 , Elise Klouman 4 , Elisante Masenga 5 , Noel Sam 5 , Kagoma S Mnyika 2 and Knut-Inge Klepp 3 1 Department of General Practice and Community Medicine, Faculty of Medicine, University of Oslo, PO Box 1046, Blindern 0318, Oslo, Norway 2 Departments of Epidemiology and Biostatistics, Muhimbili University College of Health Sciences, PO Box 65015, Dar es Salaam, Tanzania 3 Department of Nutrition, Faculty of Medicine, University of Oslo, PO Box 1046, Blindern 0318, Oslo, Norway 4 Norwegian Institute of Public Health, Division of Infectious Disease Control, PO Box 4404, Nydalen 04030, Oslo, Norway 5 Kilimanjaro Christian Medical Centre, PO Box 3010, Moshi, Tanzania * Corresponding author, e-mail: eliajelia@yahoo.co.uk This study aimed at describing the prevalence and incidence of HIV-1 and change in the prevalence of reproductive tract infections (RTIs) and sexual risk behaviours in the rural Kilimanjaro region of Tanzania. Two cross-sectional surveys among the total village population of Oria were conducted in 1991 and 1993. All individuals with a permanent address in the village were registered and invited to participate. After informed consent, participants gave blood for HIV-1 testing. Participants aged 15–44 years were interviewed regarding their socio-demographic characteristics and sexual risk behaviours and underwent genital examination and testing for RTIs. In 1991 and 1993, respectively, 3 239 (83.6%) and 2 191 (76.9%) individuals in the village participated. Prevalence of HIV-1 increased from 1.3% to 1.8%, but the difference was not significant (p = 0.17). HIV-1 incidence was 13.0/1000 person-years-at-risk (PYAR) for women and 4.3/1000 PYAR for men (relative risk was 3.0; 95% CI: 1.12–8.16). There was a significant increase in the prevalence of gonorrhoea, bacterial vaginosis and vaginal candidiasis (p < 0.001). The percentage of individuals who reported having multiple sexual partners during the 12 months preceding the survey increased from 12.9% to 24.1% (p < 0.001). The results suggest that RTIs and HIV-1 infections increased in this population in the early 1990s. Women were at higher risk of HIV-1 infection as compared to men. Sexual risk behaviours and RTIs may have contributed to HIV-1 transmission in this community. The data collected may help to inform the future design and evaluation of various intervention measures. Keywords: Africa, bacterial vaginosis, candidiasis, chlamydia, epidemiological synergy, gonorrhoea, incidence, sequelae The incidence of HIV-1 infection is relatively high in Tanzania (Swai, Somi & Kwesigabo, 2005), with estimated prevalence at 8.8%. Women appear at higher risk of becoming infected than their male counterparts (Klouman, Masenga, Klepp, Sam, Nkya & Nkya, 1997; this study). Multiple sexual partners, alcohol consumption, a low rate of condom use, frequent travel, lack of male circumcision and high rates of reproductive tract infections (RTIs) are among the factors associated with the risk of HIV-1 infection in different parts of the country (Killewo, Sandstrom, Bredberg-Raden, Mhalu, Biberfeld & Walls, 1993; Klouman et al., 1997; Kwesigabo, Killewo, Godoy, Urassa, Mbena, Mhalu, Biberfeld, Wall & Sandstrom, 1998; Kapiga, Sam, Shao, Renjifo, Masenga, Kiwelu, Monongi, Fawzi & Essex, 2002; Msuya, Mbizyo, Stray-Pedersen, Sundby, Sam & Hussain, 2002). RTIs continue to be a major public health problem in Tanzania, potentiating HIV-1 transmission as well as causing social and economic consequences (Killewo et al., 1993; Klouman et al., 1997; Kwesigabo et al., 1998; Kapiga et al., 2002; Msuya et al., 2002; Swai, et al., 2005). It is estimated that about 10% of people attending urban health centres and 7% of those attending rural health centres are infected with curable RTIs (Swai et al., 2005). A few available aetiological RTI studies (e.g. Killewo et al., 1993; Grosskurth, Mosha, Todd, Mwijarubi, Klokke, Senkoro, Mayaudi, Changalucha, West & Hayes, 1995; Klouman et al., 1997; Kapiga et al., 2002; Msuya et al., 2002) have shown that the prevalence of various RTIs is high in the country. RTIs and HIV-1 infections have a complex recipro- cal relationship described as ‘epidemiological synergy’ wherein RTIs increase the infectiousness of HIV-1 infected Introduction