A review of statistical methods for estimating the risk of vertical human immunodeficiency virus transmission.
BACKGROUND: Estimation of the risk of vertical transmission of human immunodeficiency virus (HIV) has been complicated by the lack of a reliable diagnostic test for paediatric HIV infection. METHODS: A literature search was conducted to identify all statistical methods that have been used to estimate HIV vertical transmission risk. Although the focus of this article is the analysis of birth cohort studies, ad hoc studies are also reviewed. CONCLUSIONS: The standard method for estimating HIV vertical transmission risk is biased and inefficient. Various alternative analytical approaches have been proposed but all involve simplifying assumptions and some are difficult to implement. However, early diagnosis/exclusion of infection is now possible because of improvements in polymerase chain reaction technology and complex estimation methods should no longer be required. The best way to analyse studies conducted in breastfeeding populations is still unclear and deserves attention in view of the many intervention studies being planned or conducted in developing countries. (+info)
Study of the effect of lactational bone loss on blood lead concentrations in humans.
Lactation and other clinical states of high bone turnover have been suggested to release lead (Pb) stored in bone into blood and tissues. Previous observations on the influences of lactation have been anecdotal, or at high blood Pb concentrations with varying past exposures, or complicated by postpartum fluid changes. A prospective observational study was performed to investigate possible changes in blood lead concentrations at multiple intervals during lactation for 6 months postpartum and to relate changes in blood lead concentrations to changes in bone density and other variables. Volunteer pregnant subjects (n = 58) were enrolled from a midwifery service at an academic public health hospital. Subjects were mostly Hispanic, recently immigrated, of low economic status, not receiving supplemental calcium, and had low blood Pb concentrations (2.35 +/- 2.05 microg/dl at enrollment). Bone density losses over 6 months for the group averaged -2.46 +/- 6.33% at the vertebral spine and -0.67 +/- 5.21% at the femoral neck. In predicting final bone density, apart from initial bone density only the total number of breast-feedings was a significant independent variable of the variables tested, accounting for an additional 12% of the variability. No changes in blood Pb concentrations were seen over the interval beyond 2 weeks postpartum (minimum detectable change was 0.4 microg/dl). There was no relation between the changes in bone density and changes in blood Pb or the integrated blood Pb over the 2-week to 6-month period. Normal (nonlactating) bone resorption rates contribute a large fraction of the Pb in blood during low-exposure circumstances. However, during lactation the increase in bone resorptive processes is probably relatively small with a larger decrease in deposition accounting for net bone loss, as suggested by other investigations. Thus, concomitant release of Pb from bones of lactating subjects with low blood lead concentrations on this background of high normal resorption was not large enough for detection. (+info)
Environmental contaminants and body fat distribution.
The effect of body mass index (BMI) and waist:hip ratio (WHR) on plasma levels of organochlorines [i.e., 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE)] was investigated in a sample of black and white women drawn from a population-based study in North Carolina. Organochlorine levels were determined in plasma samples from 99 women selected on the basis of race (black versus white) and quartile of the WHR (1st versus 4th). Of a panel of 20 organochlorine compounds tested, only DDE was detectable in most study subjects. Measurements of height, weight, and waist and hip circumferences were taken during an in-person interview. Information was elicited regarding dietary, residential, and breast-feeding histories. Results of multiple regression analyses indicate that black women had significantly higher plasma levels of DDE than white women. These levels were independent of BMI and WHR. BMI but not WHR was also found to be an independent predictor of DDE plasma level. These results suggest that black/white differences should be considered in studies that explore the relationship between environmental contaminants and various disease outcomes, such as breast cancer risk. In addition, BMI may affect circulating levels of contaminants and should also be considered a potentially important modifying factor for exposure to lipophilic substances. (+info)
A new tool for measuring the suckling stimulus during breastfeeding in humans: the orokinetogram and the Fourier series.
The Fourier series was used to analyse the oral movements recorded by the orokinetogram during breastfeeding in human babies. This is a new method that allows recording of oral movements without introducing any extrinsic element between the nipple and the mouth of the baby. The advantage of displaying suckling activity after fast Fourier transform (FFT) is that this algorithm allows storage, quantification and frequency analysis of the oral movements throughout a suckling bout, which enables the total oral activity to be measured. Two types of oral movements are found: slow high amplitude (SHA) and fast low amplitude (FLA). FLA movements may be derived from peristaltic movements of the tongue that result in tickling stimuli to the mechanoreceptors of the nipple and milk expression. The frequency bandwidth of oral movements is wider (0-8 Hz) than has been described previously (0-3 Hz) and this is due to the presence of the FLA oral movements. An indirect measurement of the energy of oral movements during suckling is obtained by the pattern of energy distribution used in each individual frequency band by oral movements. This pattern changes in relation to the periods of continuous and intermittent suckling activity. SHA and FLA oral movements are more intense during continuous suckling. Statistical analysis showed a correlation between the energy of SHA and FLA waves throughout the suckling bout, and also that the highest level of energy during suckling activity is displayed during the first 2 min. The novel tools described in this paper allow investigation of the role of suckling stimulus in reflex hormone release and other mother-infant interactions. (+info)
Enteropathogenic bacteria in faecal swabs of young children fed on lactic acid-fermented cereal gruels.
The influence of consumption of a lactic acid-fermented cereal gruel togwa with pH < or = 4 on the presence of faecal enteric bacteria such as campylobacter, enterohaemorrhagic Escherichia coli (EHEC:O157), enterotoxigenic Escherichia coli (ETEC), salmonella and shigella was evaluated. Under 5 years old healthy children listed in an ascending order of age were alternatively assigned and given either a lactic-acid fermented cereal gruel togwa (test diet) or an unfermented cereal gruel uji (control diet) once a day for 13 consecutive days. The presence of the enteropathogens was examined in rectal swabs collected from the children at baseline (before feeding session started), on days 7 and 13, and additionally 14 days (follow-up day) after the feeding session had stopped. The swabs were cultured on to different optimal media for respective enteropathogen and confirmed by standard microbiological and serological methods. Campylobacter spp. dominated among the enteropathogens (62% out of total) followed by Salmonella spp., ETEC and Shigella spp. Children with isolated enteropathogens in the togwa group was significantly reduced (P < 0.001) from 27.6% at baseline to 7.8, 8.2 and 12.7% on days 7, 13 and follow-up day, respectively. The effect was more pronounced in those children taking togwa > 6 times during the study period. In the control group, there was a slight decrease from 16.7% at baseline to 11.4% on day 7 and 8.1% on day 13. On the follow-up day, enteropathogens were found in 22.6% of the children, which was significantly higher than in those children taking togwa > 6 times. We conclude, that regular consumption of togwa with pH < or = 4, once a day, three times a week may help to control intestinal colonization with potential diarrhoea-causing pathogens in young children. (+info)
Studies of human immunodeficiency virus type 1 mucosal viral shedding and transmission in Kenya.
If human immunodeficiency virus type 1 (HIV-1) vaccines are to be highly effective, it is essential to understand the virologic factors that contribute to HIV-1 transmission. It is likely that transmission is determined, in part, by the genotype or phenotype (or both) of infectious virus present in the index case, which in turn will influence the quantity of virus that may be exchanged during sexual contact. Transmission may also depend on the fitness of the virus for replication in the exposed individual, which may be influenced by whether a virus encounters a target cell that is susceptible to infection by that specific variant. Of interest, our data suggest that the complexity of the virus that is transmitted may be different in female and male sexual exposures. (+info)
Transmission of human immunodeficiency virus type 1 through breast-feeding: how can it be prevented?
One-third to two-thirds of maternal transmission of human immunodeficiency virus type 1 (HIV-1) infection to breast-fed infants can be attributed to ingestion of breast milk. The presence of HIV-1 as cell-free and as cell-associated virus in milk has been documented. Several substances in breast milk may be protective against transmission, including maternal anti-HIV antibodies, vitamin A, lactoferrin, and secretory leukocyte protease inhibitor. The portal of virus entry in the infant's gastrointestinal tract is unknown but may involve breaches in mucosal surfaces, transport across M cells, or direct infection of other epithelial cells, such as enterocytes. Timing of transmission of HIV-1 during lactation should be further clarified. An early rebound of plasma viremia after withdrawal of antiretrovirals was recently detected. This rebound may reduce the benefit of antiretroviral prophylaxis when women breast-feed their infants. Interventions should be viewed from the public health perspective of risks of infant morbidity and mortality associated with breast-feeding versus risks from formula-feeding. (+info)
Breastfeeding promotion and priority setting in health.
An increase in exclusive breastfeeding prevalence can substantially reduce mortality and morbidity among infants. In this paper, estimates of the costs and impacts of three breastfeeding promotion programmes, implemented through maternity services in Brazil, Honduras and Mexico, are used to develop cost-effectiveness measures and these are compared with other health interventions. The results show that breastfeeding promotion can be one of the most cost-effective health interventions for preventing cases of diarrhoea, preventing deaths from diarrhoea, and gaining disability-adjusted life years (DALYs). The benefits are substantial over a broad range of programme types. Programmes starting with the removal of formula and medications during delivery are likely to derive a high level of impact per unit of net incremental cost. Cost-effectiveness is lower (but still attractive relative to other interventions) if hospitals already have rooming-in and no bottle-feeds; and the cost-effectiveness improves as programmes become well-established. At an annual cost of about 30 to 40 US cents per birth, programmes starting with formula feeding in nurseries and maternity wards can reduce diarrhoea cases for approximately $0.65 to $1.10 per case prevented, diarrhoea deaths for $100 to $200 per death averted, and reduce the burden of disease for approximately $2 to $4 per DALY. Maternity services that have already eliminated formula can, by investing from $2 to $3 per birth, prevent diarrhoea cases and deaths for $3.50 to $6.75 per case, and $550 to $800 per death respectively, with DALYs gained at $12 to $19 each. (+info)