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Biomedical subjects

G P Garnett

Publications and source records attributed to G P Garnett.

At least 19 recordsLinked to original sources
PubMed2006

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. Modelled prevalence, where possible based on locally collected behavioural data, was compared with the observed prevalence data in urban Haiti, urban Kenya, urban Cote d'Ivoire, Malawi, Zimbabwe, Rwanda, Uganda, and urban Ethiopia. RESULTS: Recent downturns in prevalence observed in urban Kenya, Zimbabwe, and urban Haiti, like Uganda before them, could only be replicated in the model through reductions in risk associated with changes in behaviour. In contrast, prevalence trends in urban Cote d'Ivoire, Malawi, urban Ethiopia, and Rwanda show no signs of changed sexual behaviour. CONCLUSIONS: Changes in patterns of HIV prevalence in urban Kenya, Zimbabwe, and urban Haiti are quite recent and caution is required because of doubts over the accuracy and representativeness of these estimates. Nonetheless, the observed changes are consistent with behaviour change and not the natural course of the HIV epidemic.

Adolescent↗
PubMed2006

Criteria for detecting and understanding changes in the risk of HIV infection at a national level in generalised epidemics.

Identification of causes of changes in prevalence and incidence of HIV at a national level is important for planning future prevention and intervention needs. However, the slow progression to disease and the sensitive and stigmatising nature of the associated behaviours can make this difficult. Changing rates of incidence are to be expected as an epidemic progresses, but separating background changes from those brought about by changes in behaviour and interventions requires careful analysis. This paper discusses the criteria required to determine whether observed changes in HIV prevalence are the result of changes in behaviour.

Adult↗
PubMed2006

Behavioural data as an adjunct to HIV surveillance data.

BACKGROUND: Second generation surveillance for HIV aims to improve the validity and utility of routine serial HIV prevalence data. It includes the collection of data on sexual behaviour and sexually transmitted disease prevalence. METHODS: This paper reviews the function of sexual behaviour data in HIV surveillance and the methods used to determine which behaviours are monitored and how changes in behaviour can be assessed. RESULTS: Sexual behaviour data provide a poor predictor of the future spread of HIV, but these data can provide corroboration of changes in HIV incidence and assist in attributing changes to particular aspects of risk. Significance tests should be used to assess changes in behaviour, but this requires transparent reporting of methods and sample sizes. CONCLUSIONS: Collection of behavioural data will provide important retrospective information about the HIV epidemic progress and should not be neglected because of the focus on improving HIV sero-surveillance.

Adolescent↗
PubMed2005

Risk factors of sexually transmitted infections among migrant and non-migrant sexual partnerships from rural South Africa.

In October 1998, cohorts of circular migrant men and their non-migrant sexual partners, and non-migrant men and their non-migrant sexual partners from rural South Africa were recruited and followed-up every 4 months until October 2001. At each visit, information on sociodemographic, sexual behaviour, sexually transmitted infections (STIs) and HIV was collected. In total, 553 individuals aged between 18 and 69 years were recruited. A man and his sexual partner(s) form a sexual partnership. Migration status, age, marital status, age at sexual debut, recent sexual partners and HIV status were found to be important determinants of STI. The risk of STI varies (sigma2 = 1.45, P < 0.001) significantly across sexual partnerships even after controlling for important determinants. The variance implies substantial correlation (0.59) between members of the same sexual partnership. Ignoring this correlation leads to incorrect inference. Migration contributes significantly to the spread of STIs. Community interventions of HIV/STI should target co-transmitter sexual partnerships rather than high-risk individuals.

Adolescent↗
PubMed2005

HIV infection and reproductive health in teenage women orphaned and made vulnerable by AIDS in Zimbabwe.

AIDS has increased the number of orphans and vulnerable children (OVCs) in sub-Saharan Africa who could suffer detrimental life experiences. We investigated whether OVCs have heightened risks of adverse reproductive health outcomes including HIV infection. Data on HIV infection, sexually transmitted infection (STI) symptoms and pregnancy, and common risk factors were collected for OVCs and non-OVCs in a population survey of 1523 teenage children in eastern Zimbabwe between July 2001 and March 2003. Multivariate logistic regression was used to test for statistical association between OVC status, adverse reproductive health outcomes and suspected risk factors. Amongst women aged 15-18 years, OVCs had higher HIV prevalence than non-OVCs (3.2% versus 0.0%; p = 0.002) and more common experience of STI symptoms (5.9% versus 3.3%; adjusted odds ratio = 1.75, 95% CI 0.80-3.80) and teenage pregnancy (8.3% versus 1.9%; 4.25, 1.58-11.42). OVCs (overall), maternal orphans and young women with an infected parent were more likely to have received no secondary school education and to have started sex and married, which, in turn, were associated with poor reproductive health. Amongst men aged 17-18 years, OVC status was not associated with HIV infection (0.5% versus 0.0%; p = 1.000) or STI symptoms (2.7% versus 1.6%; p = 0.529). No association was found between history of medical injections and HIV risk amongst teenage women and men. High proportions of HIV infections, STIs and pregnancies among teenage girls in eastern Zimbabwe can be attributed to maternal orphanhood and parental HIV. Many of these could be averted through further female secondary school education. Predicted substantial expanded increases in orphanhood could hamper efforts to slow the acquisition of HIV infection in successive generations of young adults, perpetuating the vicious cycle of poverty and disease.

Adolescent↗
PubMed2005

A systematic review of the epidemiology and interaction of herpes simplex virus types 1 and 2.

OBJECTIVES: To explore epidemiological evidence about the interaction of herpes simplex virus (HSV) 1 and HSV-2 infections. METHODS: A systematic review was undertaken of published epidemiological studies describing the pattern of HSV-1 or HSV-2 by age, and the coincidence of the two viral infections. RESULTS: In cross sectional studies the unadjusted odds of HSV-2 are greater in those with HSV-1 infection in study populations categorised as "low risk" (p = 0.06) and across European populations (p = 0.001). This was not evident in "high risk" populations or in the United States. This increased risk of HSV-2 in those with HSV-1 infection does not agree with the results of prospective studies where there is a non-significant trend towards a lower risk of HSV-2 infection associated with previous HSV-1 infection. CONCLUSIONS: "Low risk" and European populations have a relatively low HSV-2 seroprevalence and infection is more concentrated in those with characteristics putting them at high risk for both HSV-1 and HSV-2. This confounding could mask any protective effect of HSV-1, which is hinted at, but not demonstrated, in prospective and adjusted studies.

Herpes Simplex↗
PubMed2005

Patterns of uptake of treatment for self reported sexually transmitted infection symptoms in rural Zimbabwe.

OBJECTIVES: To determine the extent of self reported symptoms perceived to be related to sexually transmitted infections and the patterns of subsequent treatment seeking behaviour in a predominantly rural population of Zimbabwe. METHODS: A population based survey of 4331 men and 5149 women was conducted in rural Zimbabwe during 1998-2000. Structured confidential interviews collected data on self reported sexually transmitted infection symptoms, treatment seeking behaviour, sociodemographic characteristics, and sexual behaviour. RESULTS: 25% of men aged 17-54 years report experiencing genital sores and 25% of men report experiencing urethral discharge; 30% of women aged 15-44 years report experiencing vaginal discharge. The lifetime number of sexual partners, age, and years of sexual activity were all significant predictors of symptoms for both men and women (all p values <0.001). 92% of men and 62% of women had sought treatment for their symptoms in the past year (p value <0.001). Men and women were equally likely to have sought treatment at a local hospital or clinic, but women were much less likely than men to have sought treatment at a different hospital or clinic. Among those who had sought treatment, men sought treatment faster than women and were more likely to report being "very satisfied" with their treatment than women. CONCLUSIONS: The gender differences in treatment seeking are of major concern for control efforts and further work on determining the reasons for these should be a priority. This would inform the likely impact of both increasing availability of local services and further reducing the stigma faced by those wishing to access such services.

Adolescent↗
PubMed2004

The potential epidemiological impact of a genital herpes vaccine for women.

BACKGROUND: In two phase III vaccine trials immunisation of women previously uninfected by herpes simplex virus provided protection against genital herpes disease. In deciding policy, an evaluation of the epidemiological impact of the partial protection provided by the vaccine should be considered. METHODS: A sex and sexual activity stratified deterministic differential and partial differential equation model of the natural history of herpes simplex virus type 2 (HSV-2) and the impact of vaccination is developed and analysed. To explore the role of vaccination, the pattern of viral shedding and the transmission of infection during sexual acts within sexual partnerships are described. RESULTS: Using literature derived estimates of parameter values and assuming efficacy in only 40% of women the impact of the vaccine depends on assumptions made about its action. The vaccine has a limited impact if it only prevents disease but a more substantial impact if it reduces asymptomatic viral shedding, which it could do indirectly by preventing infection or directly by modifying the biology of the infection. Concern over the implications of a vaccine that prevents disease but has no impact on viral shedding was addressed in a worst case scenario. Here there is a modest increase in the incidence of infection in both men and women but an increase in disease prevalence in men alone, since the virus directly protects some women from disease. CONCLUSIONS: Results suggest that a herpes vaccine should be used universally and that a vaccine that only protects HSV-1-/2- women can paradoxically have a significant epidemiological impact, the scale of which depends upon changes in patterns of viral shedding.

Clinical Trials, Phase III as Topic↗
PubMed2004

Investigating ethnic inequalities in the incidence of sexually transmitted infections: mathematical modelling study.

OBJECTIVES: To investigate ethnic differences in rates of gonorrhoea using empirical sexual behaviour data in a simple mathematical model. To explore the impact of different intervention strategies in this simulated population. METHODS: The findings from cross sectional studies of gonorrhoea rates and sexual behaviour in three ethnic groups in south east London were used to determine the parameters for a deterministic, mathematical model of gonorrhoea transmission dynamics, in a population stratified by sex, sexual activity (rate of partner change), and ethnic group (white, black African, and black Caribbean). We compared predicted and observed rates of infection and simulated the effects of targeted and population-wide intervention strategies. RESULTS: In model simulations the reported sexual behaviours and mixing patterns generated major differences in the rates of gonorrhoea experienced by each subpopulation. The fit of the model to observed data was sensitive to assumptions about the degree of mixing by level of sexual activity, the numbers of sexual partnerships reported by men and women, and the degree to which observed data underestimate female infection rates. Interventions to reduce duration of infection were most effective when targeted at black Caribbeans. CONCLUSIONS: Average measures of sexual behaviour in large populations are inadequate descriptors for the epidemiology of gonorrhoea. The consistency between the model results and empirical data shows that profound differences in gonorrhoea rates between ethnic groups can be explained by modest differences in a limited number of sexual behaviours and mixing patterns. Targeting effective services to particular ethnic groups can have a disproportionate influence on disease reduction in the whole community.

Adolescent↗
PubMed2002

Assessment of the factors associated with flavivirus seroprevalence in a population in Southern Vietnam.

Dengue and Japanese encephalitis flaviviruses cause severe disease and are hyperendemic in southern Vietnam. This study assesses associations between sociodemographic factors and flavivirus seroprevalence in this region. Sera were collected from 308 community and hospital-based subjects between April 1996 and August 1997 and tested with an indirect ELISA. The factors associated with seroprevalence were assessed using multivariate logistic regression. In this first report of adjusted prevalence odds ratios (POR) for flavivirus infection in Vietnam, seropositivity was associated with increasing age in children (multiple regression coefficients for a child compared to an adult = -4.975 and for age in children = 0.354) and residence in the city compared to surrounding rural districts. The association with age indicates that subjects were most likely to have acquired infection in early childhood. This is key to the design of Vietnamese health education and immunization programmes.

Adolescent↗
PubMed2002

The potential role of suppressive therapy for sex partners in the prevention of neonatal herpes: a health economic analysis.

BACKGROUND: The development of suppressive therapy and type specific tests for herpes infections allow for screening to reduce the risk of neonatal herpes. OBJECTIVES: To assess the potential effectiveness, cost effectiveness, and benefit of suppressive therapy among herpes simplex virus serodiscordant sex partners during pregnancy. METHODS: Decision and economic analyses are used to compare the incidence and costs of neonatal herpes in California (2000) for three interventions: (1) no management; (2) current guidelines (caesarean delivery for women with lesions); (3) screening for women at risk and use of suppressive treatment in sex partners. RESULTS: Screening and suppressive therapy are the most effective interventions, while current guidelines have limited effectiveness, but the latter provide the most cost effective results. CONCLUSIONS: While current guidelines are cost saving, they forgo a potential 82% decrease in neonatal herpes incidence that would be possible with screening and suppressive therapy if society were willing to pay the necessary US$363 000 per case prevented. To evaluate HSV screening and drug therapy completely, clinical trials and an economic assessment of infant mortality "value" to society are required.

Acyclovir↗
PubMed2002

The geographical and temporal evolution of sexually transmitted disease epidemics.

In developing appropriate interventions to control sexually transmitted infections (STIs) it is important to understand the distribution of infections, and how this distribution is influenced by the dynamic nature of epidemics. The epidemiology of STIs has been described as a series of phases, which loosely positions a population within the history of an epidemic. The relation between a mathematical theory describing STI epidemiology and the taxonomy of "phases" is explored in this review of the transmission dynamics of STIs. The likelihood of spread and persistence of infection depends upon the basic reproductive number, whereas the endemic prevalence of infection depends upon the way in which heterogeneity in risk focuses the density dependent constraints limiting the spread of infection. All interventions aimed at reducing the prevalence and incidence of infection must act through the reproductive number. The key parameters determining the reproductive number and the relevance of risk behaviours depend upon the biology of the particular infection. The division between high transmission probability, short duration infections and low transmission probability, long duration infections is explored.

Disease Outbreaks↗
PubMed2002

The impact of the phase of an epidemic of sexually transmitted infection on the evolution of the organism.

The evolution of any sexually transmitted organism will be influenced by prevailing epidemiological interactions. The optimum strategy for an organism to overcome treatment, either through drug resistance or cryptic infections, depends upon whether the method for identifying patients is passive (treating symptoms alone favours asymptomatic organisms) or active (screening favours resistant organisms). The use of mathematical models of competing strains of infection allows theoretical predictions for the outcome of evolution under a range of assumptions about potential phenotypes. The course of pathogen evolution has implications for the success of interventions, but the predictions presented need to be tested at the level of the community in carefully monitored interventions.

Drug Resistance↗