Has the HIV Epidemic in Rural Mwanza, Tanzania Reached a Plateau?
Total Page:16
File Type:pdf, Size:1020Kb
Tanzania Journal of Health Research Volume 10, No. 3, July 2008 117 Has the HIV epidemic in rural Mwanza, Tanzania reached a plateau? W. MWITA1*, J. CHILONGANI1, R. WHITE2, G. MSHANA1, J. CHANGALUCHA1, F.MOSHA1, D. ROSS2, B. ZABA1, 2, and J. TODD3 1 National Institute for Medical Research, P. O. Box 1462, Mwanza, Tanzania 2 The London School of Hygiene & Tropical Medicine, London, U.K. 3 Medical Research Council Programme on AIDS in Uganda, Uganda Virus Research Institute, Entebbe, Uganda _________________________________________________________________________________________ Abstract: Data from studies in Mwanza Region in Tanzania suggest stabilising HIV prevalence. The objective was to determine the factors that may have contributed to the relatively stable pattern of the HIV prevalence observed in the comparison communities of the Mwanza STD treatment trial in rural Mwanza Region, Tanzania between 1991 and 2001. Socio-demographic, sexual behaviour and HIV prevalence data in two surveys conducted 10 years apart in the same communities using similar sampling schemes were compared. The age standardised HIV prevalence was 3.8% (95% CI: 3.2–4.6) in 1991 and 4.3% (95% CI: 2.8–6.4) in 2001 for males (Z= - 0.56, P= 0.58); and 4.5% (95% CI: 3.8–5.3) in 1991 and 3.9% (95% CI: 2.6–5.6) in 2001 for females (Z= 0.64, P= 0.52). Participants in the 2001 survey reported significantly fewer lifetime and recent sexual partners (12 months), Sexually Transmitted disease syndromes (12 months) and significantly more condom use at last sex with casual partners than those in the 1991 behaviour survey. We conclude that STD/ HIV infection prevention activities in rural Mwanza may be responsible for changes in risky sexual behaviour and have successfully impeded the spread of HIV infection. These activities should therefore be enhanced to reduce HIV incidence even further. In addition, modelling studies are needed to assess whether mobility of HIV infected people out of rural communities may stabilise the prevalence of the HIV infection in the general populations. _________________________________________________________________________________________ Key words: HIV, prevalence, trend, sexual behaviour, population mobility, Tanzania Introduction migration of HIV positive people out of the communities or when mortality of those infected is greater or equal to It is estimated that, by the end of 2007, 33 million incidence (UNAIDS, 1999). In an endemic steady state, people worldwide were infected with the human prevalence of HIV infection is the product of incidence immunodeficiency virus (HIV), 68% of whom live in and the mean duration of infection (UNAIDS, 1999). sub-Saharan Africa (UNAIDS, 2007). The distribution In Mwanza City in Tanzania, sentinel surveillance of HIV in sub-Saharan Africa is uneven, some countries data among pregnant women, population based cross- having an adult HIV prevalence as high as 25%, while in sectional and cohort studies among adults have shown other countries the prevalence is below 1% (UNAIDS, a stable HIV prevalence of around 12% from 1989 to 2007). Within countries the aggregate HIV prevalence 2000 (Barongo et al., 1990; Senkoro et al., 2000; MoH, usually masks a large difference between rural and urban 2005). Similar studies have shown that the prevalence areas (WHO, 2000; Barongo et al., 1992). of HIV in urban Bukoba in north-western Tanzania The Joint United Nations Programme on HIV/ declined from 29% to 15% in women and from 17% AIDS (UNAIDS) suggests that, in the natural course to 10% in men from 1987 to 1996 (Kwesigabo et al., of HIV/AIDS epidemic, the relationship between 1998; Kwesigabo, 2000; MoH, 2000). Studies within prevalence and incidence varies as the epidemic ages. the Kisesa open cohort in rural Mwanza Region, For instance, in an early stage of the epidemic, incidence Tanzania (20 km east of Mwanza City) have shown and prevalence of HIV infection grows exponentially in that the HIV prevalence among 15-44 year old adults the population at risk. As the epidemic grows and the increased from 5.9% (6.7% in females, 4.9% in males) number of people infected increases, the reproductive in 1994 to 6.6% (8.0% in females, 5.0% in males) in rate of infection is reduced which slows down the 1996 with an incidence of 0.8/100 person-years of growth of incidence. Eventually, incidence declines observation (PYO). The HIV prevalence increased while prevalence continues to grow. The prevalence further to 8.1% (9.5% in females, 6.7% in males) in of HIV decreases or levels off only when there is high 1999 with an incidence of 1.3/100PYO and remained * Correspondence: Dr. Wambura Mwita; E-mail: [email protected] 118 Tanzania Journal of Health Research Volume 10, No. 3, July 2008 high in 2003, 7.9% (8.2% in females, 7.6% in males) 20 clusters and cluster sampling was used to select 7-9 with an incidence of 1.2/100PYO (Mwaluko et al., 2003; clusters in each community. All eligible adults were M. Urassa unpubl.). The prevalence of HIV in Mwanza asked to attend at a convenient place in the cluster for Region in 2003/04 among 15-49 year old adults was interviews, clinical examination and for provision of reported to be 7.2% (7.0% in females, 7.5% in males) blood sample for HIV testing. Those who did not attend (THIS, 2005). were followed up at their homes and, where possible, In 1991, the HIV prevalence among 15-54 year recruited. A survey of sexual behaviour was carried out old adults in six communities of rural Mwanza Region, 4-14 months after the baseline survey on a sub-sample Tanzania was 4.7% in females and 4.1% in males of one in eight individuals selected from the cohort by (Grosskurth et al., 1995a). These six communities acted simple random sampling (Munguti et al., 1997). The as the comparison arm within an STD treatment trial that follow-up survey of this trial was conducted in 1993 was conducted between 1991 and 1994. The incidence (Grosskurth et al., 1995b). of HIV was 0.9/100PYO and mortality due to HIV was In 2001, we returned to the six comparison arm 0.3/100 PYO (Grosskurth et al., 1995a,b; Todd et al., communities to conduct a cross-sectional study on the 1997). If this trend had continued, the HIV prevalence association between population mobility and the spread would therefore have been higher in 2001 (10 years of HIV. Within the six communities, a similar sampling later) than in 1991 at the baseline of the trial. A cross- scheme was used to randomly select six clusters. In sectional study was conducted in 2001 in the same six each selected cluster, 14 neighbouring households were communities which showed that the prevalence of HIV randomly selected and all adults aged 15-54 years from had not risen as expected (See Table 1). these households were asked to participate in this study. We hypothesized that this finding could be Those who consented to participate were interviewed, explained by epidemiological factors such as the effect examined and asked to provide a finger prick blood of HIV mortality, population mobility and changes specimen. Households were revisited at least twice in determinants of HIV incidence and STD services to look for previously absent household members or weaknesses in the study design such as sample between 1-7 days later while the teams were still in incomparability and random chance. the community. A follow-up to the 2001 study was conducted in 2004 to investigate the association between The objective of this analysis was to determine HIV incidence and changes of household residence. which of the above factors might have contributed to the relatively stable pattern of the HIV prevalence observed In both the 1991 and 2001 survey the methods in the comparison arm of the Mwanza STD treatment were similar. Structured questionnaires were used to trial in rural Mwanza Region, Tanzania between 1991 collect socio-demographic and sexual behaviour data. All and 2001. respondents who presented with symptoms suggestive of sexually transmitted diseases (STDs) were offered free Materials and Methods treatment. Blood was tested for HIV-1 antibodies using two independent enzyme-linked immunosorbent assays Study area - GACELISA (Murex & Organon, Organon Technical, The study was conducted in the rural areas of Mwanza UK) in 1991 and UNIFORM II (Vironostika) and Region on the southern shores of Lake Victoria in ENZYGNOST (Dade Behring AG) in 2001. Western northwest Tanzania (see Figure 1). Mwanza Region Blot and ENZYGNOST tests were used to confirm covers an area of 35,872 square Km and had a HIV sero-positivity in the 1991 and in the 2001 survey, population of about 3 million (50% women) in 2002 respectively. Only blood samples that were reactive to (URT, 2003). the confirmatory test were defined to be HIV positive. The study protocols were approved by the Data collection Research Ethics Review Committee of the Medical To evaluate the impact of the introduction of syndromic Research Coordinating Committee, Tanzania, and the treatment of STDs onto local government health Ethics Committee of the London School of Hygiene and facilities on HIV incidence, approximately 12,000 adults Tropical Medicine of the United Kingdom. aged 15-54 years were recruited in 12 communities of rural Mwanza Region (6 intervention, 6 comparison) Data analysis in 1991 (Grosskurth et al., 1995a; Hayes et al., 1995). HIV sero-prevalence and incidence data from the two Each of these 12 trial communities was divided into surveys were compared using direct standardisation from Tanzania Journal of Health Research Volume 10, No. 3, July 2008 119 the 2002 Mwanza rural population census (URT, 2003). A larger proportion of females than males was We also compared data for relevant socio-demographic interviewed in 2001 than in 1991 (the sex ratio was and sexual behaviour characteristics in 1991 and 2001 0.88:1 in the 1991/92 and 0.75:1 in the 2001 surveys, including age, religion, occupation, education, age of respectively).