Factors related to attrition in a cohort study of HIV in Malawi

Background: Longitudinal studies face power reduction due to loss to follow up (LTFU). Bias may also arise because of differences between those who stay in the study and those who are LTFU We studied factors associated with LTFU in a cohort of HIV sero-negative and sera-positive mothers in urban Malawi.Objective: To bridge the existing gaps by examining the factors associated with attrition.Design: Longitudinal study.Setting: Queen Elizabeth Central Hospital (QECH) and the Kamuzu Central Hospital in Blantyre, Malawi.Subjects: One thousand three hundred and fifty three women who attended the prenatal clinic, between October 1989 and October 1990 were recruited as part of a study to determine rates and risk factors of sero-prevalence and sera-conversion of HIV -1 among this cohort.Results: In this cohort study, 1353 women were enrolled at delivery and 1188 (88%) returned for the first follow-up visit at three months post-partum. Of those who returned, 177 (15%) were subsequently lost during the remaining months of follow-up. The main predictors of L TFU were younger maternal age, lower educational level of the father, HIV infection of the mother, lower birth weight of the index child and mother not being married.Conclusions: Researchers planning studies in developing countries should consider the impact of lower education and poorer infant health on study retention in developing countries

Temporal stability in the genetic structure of Sarcoptes scabiei under the host-taxon law: empirical evidences from wildlife-derived Sarcoptes mite in Asturias, Spain

<p>Abstract</p> <p>Background</p> <p>Implicitly, parasite molecular studies assume temporal genetic stability. In this study we tested, for the first time to our knowledge, the extent of changes in genetic diversity and structure of <it>Sarcoptes </it>mite populations from Pyrenean chamois (<it>Rupicapra pyrenaica</it>) in Asturias (Spain), using one multiplex of 9 microsatellite markers and <it>Sarcoptes </it>samples from sympatric Pyrenean chamois, red deer (<it>Cervus elaphus</it>), roe deer (<it>Capreolus capreolus</it>) and red fox (<it>Vulpes vulpes</it>).</p> <p>Results</p> <p>The analysis of an 11-years interval period found little change in the genetic diversity (allelic diversity, and observed and expected heterozygosity). The temporal stability in the genetic diversity was confirmed by population structure analysis, which was not significantly variable over time. Population structure analysis revealed temporal stability in the genetic diversity of <it>Sarcoptes </it>mite under the host-taxon law (herbivore derived- and carnivore derived-<it>Sarcoptes </it>mite) among the sympatric wild animals from Asturias.</p> <p>Conclusions</p> <p>The confirmation of parasite temporal genetic stability is of vital interest to allow generalizations to be made, which have further implications regarding the genetic structure, epidemiology and monitoring protocols of the ubiquitous <it>Sarcoptes </it>mite. This could eventually be applied to other parasite species.</p