Behaviour change in generalised HIV epidemics: impact of reducing cross-generational sex and delaying age at sexual debut.

Background: Sexual behavioural change is essential to prevent HIV infections in Africa and statistical analysis of risk factors at the individual-level may be used to design interventions. The importance of reducing cross-generational sex (young women having sex with older men) and delaying age at first sex on the spread of HIV at the population-level has been presumed but not scientifically investigated and quantified.

Methods: A mathematical model of heterosexual spread of HIV was developed to predict the population-level impact of reducing cross-generational sex and delaying sexual debut.

Appropriate evaluation of HIV prevention interventions: from experiment to full-scale implementation.

Background: Preventing HIV infection is still an essential goal in tackling the HIV/AIDS pandemic. Remarkably little is known about how best to reduce HIV incidence because most trials focus on the reduction of risk behaviours and assume an effect on HIV incidence.

Objective: To discuss the evidence for the effectiveness of HIV prevention strategies, exploring the different types of evidence available: individual and community randomised controlled trials, and observational studies.

Individual freedom versus collective responsibility: too many rights make a wrong?

: Individuals might reasonably expect the freedom to make their own decisions regarding their health. However, what happens when an individual's wishes conflict with what is in that individual's best interests? How far should an individual's rights be restricted for his or her own benefit? Similarly, what limitations should be placed on an individual's behaviour when that person's wishes go against what is good for the population in general? Here we discuss the issues that can arise when the rights of individuals conflict with individual and population benefits in relation to infectious diseases.

Assessing adult mortality in HIV-1-afflicted Zimbabwe (1998 -2003).

Objective: To compare alternative methods to vital registration systems for estimating adult mortality, and describe patterns of mortality in Manicaland, Zimbabwe, which has been severely affected by HIV.

Methods: We compared estimates of adult mortality from (1) a single question on household mortality, (2) repeated household censuses, and (3) an adult cohort study with linked HIV testing from Manicaland, with a mathematical model fitted to local age-specific HIV prevalence (1998 -2000).

Findings: The crude death rate from the single question (29 per 1000 person-years) was roughly consistent with that from the mathematical model (22 -25 per 1000 person-years), but much higher than that from the household censuses (12 per 1000 person-years).

Declines in HIV prevalence can be associated with changing sexual behaviour in Uganda, urban Kenya, Zimbabwe, and urban Haiti.

Objective: To determine whether observed changes in HIV prevalence in countries with generalised HIV epidemics are associated with changes in sexual risk behaviour.

Methods: A mathematical model was developed to explore the relation between prevalence recorded at antenatal clinics (ANCs) and the pattern of incidence of infection throughout the population. To create a null model a range of assumptions about sexual behaviour, natural history of infection, and sampling biases in ANC populations were explored to determine which factors maximised declines in prevalence in the absence of behaviour change.

HIV decline associated with behavior change in eastern Zimbabwe.

Few sub-Saharan African countries have witnessed declines in HIV prevalence, and only Uganda has compelling evidence for a decline founded on sexual behavior change. We report a decline in HIV prevalence in eastern Zimbabwe between 1998 and 2003 associated with sexual behavior change in four distinct socioeconomic strata. HIV prevalence fell most steeply at young ages-by 23 and 49%, respectively, among men aged 17 to 29 years and women aged 15 to 24 years-and in more educated groups.

Why large-scale climate indices seem to predict ecological processes better than local weather.

Large-scale climatic indices such as the North Atlantic Oscillation are associated with population dynamics, variation in demographic rates and values of phenotypic traits in many species. Paradoxically, these large-scale indices can seem to be better predictors of ecological processes than local climate. Using detailed data from a population of Soay sheep, we show that high rainfall, high winds or low temperatures at any time during a 3-month period can cause mortality either immediately or lagged by a few days.

Linguistic competence in paediatric closed head injury.

The purpose of this investigation was to examine the effects of age at onset of traumatic brain injury on the linguistic competence of children and adolescents who sustained closed head injuries (CHI) that cause diffuse brain damage. The Test of Language Competence-Expanded Edition (TLC-E), a standardized test of subtle language abilities, was administered to 20 children who sustained severe CHI. The study determined whether 10 subjects who experienced CHI at a pre-adolescent age (4 to 11 years) and 10 subjects who experienced CHI at an adolescent age (13 to 18 years) showed quantitative differences in linguistic competence as measured by the TLC-E Test.