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Biomedical subjects

B Zaba

Publications and source records attributed to B Zaba.

At least 19 recordsLinked to original sources
PubMed2007

HIV epidemic trend and antiretroviral treatment need in Karonga District, Malawi.

We describe the development of the HIV epidemic in Karonga District, Malawi over 22 years using data from population surveys and community samples. These data are used to estimate the trend in HIV prevalence, incidence and need for antiretroviral treatment (ART) using a simple mathematical model. HIV prevalence rose quickly in the late 1980s and early 1990s, stabilizing at around 12% in the mid-1990s. Estimated annual HIV incidence rose quickly, peaking in the early 1990s at 2.2% among males and 3.1% among females, and then levelled off at 1.3% among males and 1.1% among females by the late 1990s. Assuming a 2-year eligibility period, both our model and the UNAIDS models predicted 2.1% of adults were in need of ART in 2005. This prediction was sensitive to the assumed eligibility period, ranging from 1.6% to 2.6% if the eligibility period was instead assumed to be 1.5 or 2.5 years, respectively.

Adolescent↗
PubMed2006

HIV prevalence and sexual behaviour changes measured in an antenatal clinic setting in northern Tanzania.

OBJECTIVES: To assess the feasibility of collecting sexual behaviour data during HIV surveillance in antenatal care (ANC) clinics, and to establish whether these data can provide information about the correlates of HIV infection in this population. METHODS: Sexual behaviour surveys were conducted in the context of two HIV sentinel surveillance rounds in 11 ANC clinics in north west Tanzania between 2000 and 2002. Responses of individual women were anonymously linked to their HIV status. Three clinic catchment areas overlapped with a community based longitudinal study, which provided independent estimates of HIV prevalence and sexual behaviour. Changes between rounds and differentials between clinics were assessed and a two level logistic regression model used to identify behavioural and contextual correlates of HIV in 3689 women under 25 years of age. RESULTS: Women attending clinics were willing to participate in the study. The sexual behaviour data obtained were internally consistent and tallied reasonably well with sexual behaviour data collected in the community overlapping the clinic catchment. Clear relations emerged between HIV infection and measures of sexual exposure: OR 1.20 (95% CL 1.12 to 1.28) for each year of premarital exposure and 1.09 (1.04 to 1.16) for each year after first marriage; background prevalence OR 1.15 (1.04 to 1.26) associated with each percentage point increase in background prevalence at the clinic; and certain partnership variables such as partner's age OR 0.58 (0.45 to 0.76) if partner less than 10 years older. CONCLUSION: Conducting sexual behaviour surveys in the context of ANC clinics surveillance is feasible and yields useful data.

Adult↗
PubMed2004

Methodological lessons from a cohort study of high risk women in Tanzania.

OBJECTIVES: To describe the development, characteristics, and follow up of a high risk cohort of women in Tanzania. Differences in social background and sexual behaviour of women working in traditional and modern alcohol selling workplaces are shown. METHODS: Data from questionnaires four months before the enrollment of the cohort, at enrollment, and at 32 months were compared. Key informant interviews, social mapping exercises, and focus group discussions were held before the start of the cohort. RESULTS: In the absence of organised prostitution, two different groups of women with high risk exposure were identified during the baseline survey: female workers in modern alcohol selling places such as bars, guesthouses, and restaurants (barmaids) and in traditional places (local brew sellers). Overall, the population had a mean age of 27.7 years with barmaids tending to be younger (24.3 years) than local brew sellers (34.2 years). The main duration of stay in the current workplace was 2.1 years (barmaids 0.9 years; local brew sellers 4.1 years). Barmaids were more likely to have paying casual sex partners than local brew sellers and used condoms more regularly. Local brew sellers tend to be more stable with only 10% lost to follow up after 32 months compared with 24.4% of the bar workers. CONCLUSIONS: Preliminary work revealed major differences in characteristics and behaviour between women working in modern and traditional alcohol selling outlets. Thorough preparation of the study, close monitoring of the cohort, and provision of selected benefits resulted in high retention rates over a 32 month project in a highly mobile population.

Adult↗
PubMed2004

Age at first sex: understanding recent trends in African demographic surveys.

OBJECTIVES: To describe recent trends in age at first sex in African countries, identifying and making due allowances for a variety of common reporting errors. METHODS: Demographic and Health Surveys (DHS) data from six African countries conducting three or more surveys since 1985 were analysed using survival analysis techniques, combining information on virginity status and retrospective reporting of age at first sex. Hazard analysis was used to separate the effects of reporting error and compositional change and to estimate true changes in sexual debut over time. A multistate life table analysis incorporating transition to first marriage allowed cohorts to be classified according to person years spent as virgins, as sexually active unmarried, and married. RESULTS: Intersurvey comparisons generally suggested a slow secular rise in age at first sex. However, tracing birth cohorts between surveys revealed inconsistencies--median ages reported by female members of a birth cohort in their teens were generally higher than those reported when they reached their twenties, even when allowing for residence and education changes--probably a result of young, sexually active women denying they had ever had sex. Male birth cohorts tend to display the opposite kind of bias. CONCLUSIONS: Uganda, Kenya, and Ghana have experienced a more pronounced and unambiguous decline in premarital sexual activity than Tanzania, Zambia, and Zimbabwe, with statistically significant increases in age at first sex. In addition, Uganda has maintained a very short interval between onset of sexual activity and marriage for both sexes.

Adolescent↗
PubMed2002

Sociodemographic context of the AIDS epidemic in a rural area in Tanzania with a focus on people's mobility and marriage.

This analysis focuses on how sociocultural and economic characteristics of a poor semi-urban and rural population (Kisesa ward) in north west Tanzania may directly and indirectly affect the epidemiology of HIV and other sexually transmitted infections (STI). Poverty and sociocultural changes may contribute to the observed high levels of marital instability and high levels of short and long term migration in Kisesa, especially among younger adults. Marriage and migration patterns are important underlying factors affecting the spread of HIV. The most cost-effective intervention strategy may be to focus on the trading centre in which mobility is higher, bars were more common, and HIV prevalence and incidence were considerably higher than in the nearby rural villages. If resources suffice, additional work can be undertaken in the rural villages, although it is not clear to what extent the rural epidemic would be self sustaining if the interventions in the trading centre were effective.

Acquired Immunodeficiency Syndrome↗
PubMed2001

The impact of HIV/AIDS on mortality and household mobility in rural Tanzania.

OBJECTIVE: To assess the impact of the AIDS epidemic on mortality and household mobility before and after death. DESIGN: Open community cohort study with a demographic surveillance system and two sero-epidemiological surveys. METHODS: Ten rounds of demographic surveillance were completed during 1994-1998 in the study area, which has a population of about 20 000 people in a rural ward in north-west Tanzania. Households with deaths were visited for a detailed interview, including a verbal autopsy. Data on HIV status were collected in two surveys of all residents aged 15-44 years. RESULTS: Mortality rates among HIV-infected adults were 15 times higher than those among HIV-negative adults and HIV/AIDS was associated with nearly half of deaths at ages 15-44 years. Verbal autopsies without HIV test results considerably underestimated the proportion of deaths associated with HIV/AIDS. The mortality probability between 15 and 60 years was 49% for men and 46% for women and life expectancy was 43 years for men and 44 years for women. By their second birthday nearly one-quarter of the newborns of HIV-infected mothers had died, which was 2.5 times higher than among children of HIV-negative mothers. Mobility of household members before and after death was high. In 44% of households in which the head died all members moved out of the household. CONCLUSIONS: In this rural population with HIV prevalence close to 7% among adults aged 15-44 years during the mid-1990s, HIV/AIDS is having substantial impact on adult mortality. A common response to death of a head of household in this community is household dissolution, which has implications for measurement of the demographic and socio-economic impact of AIDS.

Adolescent↗
PubMed2000

Monitoring the AIDS epidemic using HIV prevalence data among young women attending antenatal clinics: prospects and problems.

OBJECTIVE: To assess the potential of antenatal surveillance data on HIV prevalence in young women as an indicator of trends in HIV incidence. DESIGN: Review of empirical data and discussion of problems encountered with surveillance systems, illustrated using cohort-component projection models. METHODS: Simple descriptive analyses are presented of prevalence and incidence data, with projection models used to explore aspects of the dynamic relationships between changes in HIV incidence and prevalence in young pregnant women for which empirical data are not yet available. Incidence changes due to change in risk among sexually active, and change in pattern of sexual debut are explored separately, and the resulting prevalence trends in pregnant women under age 25 years, and those expecting their first two births are described. RESULTS: HIV prevalence levels in young pregnant women categorized by age and by parity have different relationships to recent incidence levels. Age categorized prevalence data provide a reasonable indication of incidence under stable conditions, but may be very misleading if the age pattern of sexual debut changes. Prevalence levels categorized by parity are a reliable guide to incidence in the sexually active, but not necessarily to incidence in the population as a whole. CONCLUSIONS: Ante-natal surveillance systems should categorize prevalence data by both age and parity to aid in the interpretation of underlying incidence levels.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Measuring the impact of HIV on fertility in Africa.

OBJECTIVES: To review evidence for the impact of HIV on fertility from empirical sources pertaining to African populations and to discuss the implications for surveillance based on antenatal clinic populations. METHODS: The theoretical equivalence between the fertility rate ratio for HIV-positive to HIV-negative women and the relative odds of being infected for pregnant women compared with the general female population is demonstrated. This equivalence is used to compare fertility differentials measured in cohort studies with those calculated indirectly from antenatal clinic data. Data from case-control studies and theoretical predictions from a model of the proximate determinants of fertility and HIV incidence are used to obtain plausible explanations of the fertility differences. Estimates of population attributable change are made. RESULTS: Fertility of HIV-positive women is lower than that of HIV-negative women, in all but the youngest age-group, and the differential increases with women's age and epidemic duration. Selection for early start of sexual activity explains the reverse pattern at younger ages. Lower fertility amongst HIV-positive women causes a population attributable decline in total fertility of the order of 0.4% for each percentage point HIV prevalence in the general female population. CONCLUSIONS: In populations that do not use contraceptives, HIV-positive women have lower fertility principally as a result of foetal losses consequent to infection with HIV and coinfection with other sexually transmitted diseases; behavioural factors tend to enhance this differential. Other factors being equal, HIV prevalence estimates based on antenatal surveillance underestimate true prevalence in women in the childbearing years.

Adolescent↗
PubMed1996

Interpreting HIV seroprevalence data from pregnant women.

HIV prevalence estimates for pregnant women from unlinked anonymous surveys are becoming increasingly available and can be used to determine the prevalence of HIV in women in the same population. The ratio of prevalence in pregnant women to that in all women is influenced by HIV-related risk behaviours that are different for pregnant and nonpregnant women and also by differences in fertility level among infected and uninfected women. This ratio is affected by biases that are likely to be culturally and socially specific. A model is proposed for the qualification and quantification of these biases and hence the estimation of general female population prevalence from serosurveillance data on pregnant women.

Female↗
PubMed1996

Time-domain reflectometry studies on Halobacterium halobium and Halobacterium marismortui.

The dielectric properties of Halobacterium halobium and Halobacterium marismortui measured over the frequency range 1 MHz to 1 GHz are compared with a single-shell model for interfacial polarization. In the case of Halobacterium halobium, the model shows excellent agreement with the experimental data for reasonable values of membrane and cytoplasmic conductivity and permittivity. For Halobacterium marismortui however, an acceptable fit to the data can only be achieved by invoking a plasma membrane conductivity some three orders of magnitude larger than that of Halobacterium halobium and adding a second high-frequency dielectric dispersion. These observations confirm the findings of a previous study and are consistent with a scheme for Halobacterium marismortui involving thermodynamic compartmentalization of Na and K ions and the existence of a conductive plasma membrane.

Cell Membrane↗
PubMed1993

Time-domain dielectric spectroscopy applied to cell suspensions.

A precision difference time-domain reflectometry (TDR) technique is described for the investigation of the dielectric properties of cell suspensions. The dielectric spectra obtained for erythrocytes using TDR are comparable with those reported in previous dielectric studies employing frequency-domain technique.

Animals↗