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Biological and behavioural impact of an adolescent sexual health intervention in Tanzania: a community-randomized trial
Global Health Sciences Literature Digest
Published October 15, 2007
Journal Article

Ross DA, Changalucha J, Obasi AI, Todd J, Plummer ML, Cleophas-Mazige B, et al. Biological and behavioural impact of an adolescent sexual health intervention in Tanzania: a community-randomized trial. AIDS 2007 Sep 12;21(14):1943-55.


To evaluate the impact of a multi-component intervention program on the sexual health of adolescents. The program included HIV incidence, the prevalence or incidence of STIs, pregnancy, sexual health knowledge, attitudes and reported sexual behavior in rural Tanzania.

Study Design

A three-year cluster-randomized trial with communities as the unit of randomization, targeting adolescents entering years 5, 6, or 7 of primary school in late 1998.


The trial was conducted in 20 well-separated rural communities in Mwanza Region, Tanzania. Ten communities (58 primary schools, 18 health facilities) received the intervention; the other ten (63 primary schools, 21 health facilities) acted as comparison communities.


Nine-thousand six-hundred and forty-five adolescents, aged 14 years or more (mean 15.7 years) and living in the 20 randomized communities, were recruited in late 1998 into a cohort to evaluate the intervention. They were recruited before entering years 5, 6, or 7 of all 121 government primary schools in the 20 trial communities: 4870 adolescents in 10 intervention communities and 4775 adolescents in 10 comparison communities. Of the participants, 9219 (5103 men and 4116 women) were recruited and randomized in late 1988, while 426 young adults were recruited and randomized at interim follow-up in 2000. Cohort members who were in year 7 when the intervention commenced (January 1999) could only receive one year of the in-school program; those in year 6 could receive two years; and those in year 5 could receive the full three years of the program.


Twenty communities were allocated by randomization (restricted to balance HIV and chlamydia prevalence) to receive either a specially designed program of interventions (intervention group) or standard activities (comparison group).

The intervention had four components: community activities; teacher-led, peer-assisted sexual health education in years 5-7 of primary school; training and supervision of health workers to provide 'youth-friendly' sexual health services; and peer condom promotion and distribution. The main aims were to provide young people with the knowledge and skills to enable them to delay sexual debut; reduce sexual risk-taking if sexually active (including reducing numbers of sexual partners and promoting condom use); and increase their appropriate use of sexual health services (STI treatment, family planning). The intervention was delivered by trained government workers through existing structures and supervision systems and deliberately constrained to be affordable to ensure replication and sustainability.

Throughout the intervention, extensive process evaluation provided feedback to the intervention team. Evaluation included questionnaires to trainees before and after all training courses; quarterly supervision visits to every intervention school and clinic; observation of in-class, club and clinic sessions; annual feedback workshop with teachers; and two externally conducted evaluation surveys.

Primary Outcomes

The primary outcomes were HIV sero-incidence during follow-up and prevalence of herpes simplex virus 2 (HSV2) infection at final survey. Secondary outcomes were six further biological measures (syphilis, chlamydia, gonorrhea, and trichomonas prevalence; pregnancy test, and reported pregnancy during follow-up), five behavioral measures (sexual debut during follow-up, >1 partner in past year, first use of condom during follow-up, used condom at last sex, went to health facility for most recent STI symptoms within past year), one attitudinal measure (attitudes to sex), and three measures of knowledge (knowledge on acquisition of HIV, STIs, and pregnancy prevention) outcomes. Each attitudinal and knowledge outcome was based on the answers to three questions.

To measure impact, there were baseline interviews and urine specimen collection for all biological outcomes, a clinician exam for clinical symptoms (male and female) and signs (male) of STIs, and an offer of HIV counseling and testing. An interim follow-up survey was conducted in 2000, and a final follow-up occurred between October 2001 and April 2002, approximately three years after recruitment. At final survey, serum and urine were collected from all participants and two self-administered vaginal swabs were collected by female subjects. Attempts were made to locate cohort members for follow-up. Impact measures were based on ratios of prevalence, risks or rates, depending on the outcome measure, in the intervention and comparison groups.


Of the 9645 eligible participants, 7040 (73%) were seen at the final survey. Follow-up rates were similar in intervention (72%) and comparison (74%), and higher among male (77%) than female (69%), participants. Baseline characteristics were similar in the intervention and comparison groups. The primary findings of the study were that there was no statistically significant benefit of the intervention on the primary biological outcomes of HIV infection rate or HSV2 prevalence, but there was a significant impact on knowledge and reported attitudes with statistically significant differences in proportions of both male and female participants who answered all questions correctly. Forty-five participants (5 boys and 40 girls) sero-converted to HIV during 23,730 person-years of follow-up. After adjustment, HIV incidence was 25% lower among female subjects in the intervention communities; however, this was not statistically significant (adjusted RR 0.75, 95%CI 0.34, 1.66). Overall, 12% of male and 21% of female participants were HSV2 sero-positive at the final survey with no difference in trial groups.

There was no protective effect of the intervention on any of the other secondary biological outcomes. In fact, the prevalence of N. gonorrhea was higher among females in the intervention group. A substantial proportion of young women (similar to the comparison group) were pregnant in the intervention group at the final survey (19%), and (47%) reported having been pregnant for the first time during the three-year follow-up period.

The intervention somewhat influenced behavioral outcomes and reported sexually transmitted infection symptoms. The proportion of young men reporting sexual debut during follow-up was 60% in the intervention and 72% in the comparison communities (adjusted RR 0.84, 95%CI 0.71, 1.01). Male subjects reporting more than one sexual partner in the past year was significantly lower in the intervention (19%) than in the comparison communities (28%; adjusted RR 0.69, 95%CI 0.49, 0.95). In both cases, little difference was seen among female participants.

The proportion of participants reporting clinical symptoms and signs of STIs in the past year was lower in the intervention communities among both males (adjusted RR 0.58, 95%CI 0.41, 0.83) and females (adjusted RR 0.59, 95%CI 0.43, 0.80); however, there was no difference in the proportion to have reported seeking care at a local health facility.

The number of participants who initiated condom use at follow-up was higher in intervention communities among both male (39%) and female (38%) participants (versus 28% for both males and females in the comparison communities). However, condom use at last sex was still low in both males (29%) and females (27%) in the intervention group and similar to the comparison group.


The lack of any consistent effect of the intervention on the biological outcomes, despite substantial effects on knowledge and self-reported behavior, raises questions about the interpretation of studies relying on knowledge and self-report as outcome measures. The authors also concluded that young people in this rural Tanzanian population were at high risk of adolescent pregnancy and STIs, with low condom use and a high proportion of the cohort reporting sexual debut during the three years of follow-up. Therefore, there is an urgent need for effective and affordable preventive interventions. The trial also demonstrated that large-scale implementation of an affordable adolescent sexual health intervention using existing government staff and structures is realistic.

Quality Rating

Based on the Jadad scale for quality of randomized trials, this trial receives a score of 3 (5 maximum score). Communities were randomized, randomization was described, and loss to follow-up was tracked (reasons for loss included temporary absence, permanently relocation, refusal, or death.) Although those lost to follow-up may have been at higher risk, similar losses were seen in both groups. Limitations to the trial were that the interventions were deliberately constrained to be affordable and replicable on a large scale, and some youth only received between one year (42%) and two years (32%) of the main, in-school component.

In Context

This is an important trial, as it is the first among adolescents in Africa to measure the impact of sexual health interventions on HIV, STIs, and pregnancy with biological endpoints and compare them to knowledge, attitudes, and self-reported sexual behavior, which is known to be particularly limited among youth.(1,2,3,4,5,6) The authors suggest that, despite impacts on knowledge, reported attitudes and self-reported sexual behaviors, the lack of any consistent effect on the biological outcomes measured in the trial raises questions about the interpretation of previous studies in which improvements in self-reported sexual behaviors have been used as a proxy for reductions in HIV and STIs. This provides a strong argument for the inclusion of biological outcomes in future program evaluations. In terms of knowledge, reported attitudes, and reported behaviors, the effects on these outcomes were at least as great as those recorded in previous studies in Africa.(7,8, 9)

Programmatic Implications

The authors suggest that additional interventions may be needed. The interventions within this trial were all directed towards adolescents. However, cultural norms such as gender or age-related power relationships and fertility norms within the wider community may affect the ability of adolescents, especially young women, to change their behavior. Community-wide interventions may be needed to change these norms. In addition, the intervention in this trial may have been too brief, as 42% of adolescents only had the potential to receive one year of the in-school component of the intervention.


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