How many subjects are needed in a longitudinal birth cohort study?

One of the first decisions that needs to be taken when planning a birth cohort concerns the size of the study. This in turn will depend on the research questions to be answered and thence whether environmental exposures and outcomes are measured on a continuum or as dichotomous variables. Here we describe ways in which different birth cohorts have addressed this issue and explore the advantages of smaller detailed studies over larger less-detailed studies.     

Adipokines in cord blood and risk of wheezing disorders within the first two years of life

BACKGROUND: Adipokines are involved in the regulation of many inflammatory processes and are present at very high concentrations in cord blood of term infants. OBJECTIVE: We analysed data of a large prospective birth cohort study to examine whether adiponectin and leptin concentration in cord blood are determinants of wheezing disorders in children within the first 2 years of life. METHODS: Seven hundred and forty mothers and their newborns were included in this analysis. Adiponectin and leptin concentrations were measured in cord blood. The cumulative incidence of physician-reported asthma or obstructive bronchitis was recorded during a 2-year follow-up. RESULTS: During the first 2 years of life, asthma or obstructive bronchitis was reported by the caring paediatricians for 157 (19.6%) of the children. We found a strong interaction of cord blood adiponectin and history of atopic disease in the mother with respect to the risk of physician-reported asthma or obstructive bronchitis (P=0.006). Compared with children with cord blood levels in the middle quintile (reference category), the odds ratios for physician-reported asthma or obstructive bronchitis in the bottom quintile and top quintile were 0.14 [95% confidence interval (CI) 0.02-0.90] and 2.12 (95% CI 0.67-6.66), respectively (P for trend=0.0003), among children of mothers with a history of atopy. This association was independent of other established risk factors. Leptin levels in cord blood were not associated with risk of asthma or obstructive bronchitis. CONCLUSIONS: In children of mothers with a history of atopy, concentrations of adiponectin in cord blood could play an important role in determining risk of wheezing disorders in early childhood.     

An association between plastic mattress covers and sheepskin underbedding use in infancy and house dust mite sensitization in childhood: a prospective study

BACKGROUND: Higher house dust mite (HDM) allergen exposure during infancy has been associated with increased HDM sensitization. Infant bedding has been associated with the accumulation of varying levels of HDM. Prospective data on the relationship between infant bedding and the development of HDM sensitization has not been previously examined. OBJECTIVES: To determine if particular types of bedding used in infancy are associated with increased risk of house dust mite sensitization in childhood. METHODS: A population-based sample (n = 498) of children born in 1988 or 1989, and who were resident in Northern Tasmania in 1997, participated in this study. These children were part of a birth cohort study (1988-95), the Tasmanian Infant Health Survey. Data on infant underbedding and mattresses was available on 460 and 457 children, respectively. The main outcome measure was HDM sensitization defined as a skin prick test (SPT) reaction of 3 mm or more to the allergens of Dermatophagoides pteronyssinus and/or Dermatophagoides farinae. RESULTS: The use of either sheepskin underbedding or plastic mattress covers in infancy was associated with an increased risk of sensitization to HDM allergens at age 8 years. The adjusted risk ratio (RR) for sensitization to HDM with sheepskin in infancy was 2.27 (95% CI: 1.14, 4.55), P = 0.020. The adjusted RR for sensitization to HDM with the use of plastic mattress covers in infancy was 2.06 (95% CI: 1.22, 3.51), P = 0.007. The use of a foam mattress in infancy was not related to subsequent HDM sensitization. CONCLUSION: Infant's bedding plays a role in the development of HDM sensitization in childhood. Intervention studies to examine mite allergen levels and the role of underbedding on the development of HDM sensitization are required.     

Effect of mite-impermeable mattress encasings and an educational package on the development of allergies in a multinational randomized, controlled birth-cohort study – 24 months results of the Study of Prevention of Allergy in Children in Europe

BACKGROUND: Sensitization to house dust mite (HDM) is an important risk factor for the development of asthma and allergic disease in childhood. Higher levels of HDM allergen are linked to increased sensitization to HDM. OBJECTIVE: To study the effect of mite-impermeable mattress encasings and an educational package on the development of allergies in a newborn cohort. METHODS: Six hundred and ninety-six newborns at high risk of developing allergies were enrolled in three European countries (Germany, Austria, UK) in a prospective, randomized, controlled birth-cohort study. Children were randomly assigned to an intervention and control group. Intervention measures included the use of mite-impermeable mattress encasings for the child's bed and a simple educational package on allergen avoidance. The control group received basic information about allergies. Children were followed up at age 6, 12, 18 and 24 months. RESULTS: 80.9% of the children were followed up to the age of 24 months. No difference in the prevalence of sensitization to HDM (control vs. intervention group: 8.4% vs. 6.1%, P=0.33) or the development of symptoms (recurrent wheezing 10.3% vs. 10.7%, nocturnal cough 12.5% vs. 12.5%) or allergic diseases (asthma 3.5% vs. 5.1%, eczema 20.0% vs. 19.6%, rhinitis 28.9% vs. 25.8%) could be found between the control and intervention group. CONCLUSION: In this study, HDM avoidance did not show a protective effect on the development of sensitization to HDM or symptomatic allergy in children at age 24 months.     

Physical aggression towards others in adults with learning disabilities: prevalence and associated factors

Background Many people with learning disabilities (LD) show aggressive behaviour, but the extent of the problem and its associated factors and effects are unclear. Methods A cross‐sectional analysis was carried out using interview data from 3065 adults with LD on the Leicestershire LD Register. Physical aggression towards others was defined as carers reporting frequent (more than three times per week) and/or severe episodes. Individuals with and without aggression were compared using multiple logistic regression models for potential physical and psychological factors. Results Carers reported that 443 (14%) of adults were physically aggressive towards others. Men (P = 0.001), younger individuals (P < 0.001), people with more severe LD (P < 0.001) and those in institutional settings (P < 0.001) had a significantly higher prevalence of physical aggression. People with Down syndrome had a lower prevalence of physical aggression (P < 0.001). After adjustment, we found no relationship between aggression and the presence of epilepsy or autism. Among psychological factors, symptoms of frustration (P < 0.001) and mood swings (P < 0.001) were associated with higher levels of aggression. Failure to cope among carers was reported by 14% overall: 42% of people caring for adults with aggression said they were unable to cope compared with 10% of those caring for adults without aggression. Conclusions Physical aggression towards other people presents a significant challenge to carers of adults with LD. Further research is needed to identify aetiological factors with a view to finding effective interventions to reduce, and improve management of, this behaviour.     

Haemoglobin at time of referral prior to dialysis predicts survival: an association of haemoglobin with long-term outcomes

Haemoglobin (Hgb) levels are known to be associated with numerousadverse outcomes in both chronic kidney disease (CKD) and non-CKDpatients. This analysis evaluates the association of baseline haemoglobinlevels on survival in CKD patients, who are followed by nephrologists,irrespective of glomerular filtration rate (GFR), prior to initiationof renal replacement therapy (RRT) and erythropoietin hormonereplacement therapy. Analysis of data from the provincial database (PROMIS, PatientRegistration and Outcome Management Information System) in BritishColumbia, Canada, was undertaken. Records used for the analysisincluded all CKD patients at first registration: GFR <60ml/min/1.73 m², not yet on dialysis, starting from May 1998to October 2002, and who had complete data (defined as age andgender, diabetic status, eGFR and Hgb levels). The primary objective of this study was to determine the associationof Hgb and survival controlling for eGFR at first registrationvalue, age, gender and diabetic status. Multivariate Cox proportionalhazards analysis with time to death as outcome variable wasperformed. The cohort included 3028 patients: the mean age was 65 years,28% were diabetic, and the mean eGFR in the cohort was 21 ml/min/1.73m². The cohort is representative of the BC CKD and dialysispopulation regarding ethnicity: 64% Caucasian, 32% Asian. Medianfollow-up was 27 months, 1 year survival was 0.92, 2 year survivalwas 0.85. Hgb at initial registration is a statistically independentpredictor of survival (RR = 0.875 for every 10 g/l, 95% CI:0.835–0.917, P = 0.0001), after adjusting for age, gender,diabetic status and baseline eGFR. Further analysis, controllingfor RRT, demonstrated a similar association between Hgb andsurvival (RR = 0.853 for every 10 g/l, 95% CI: 0.799–0.910,P = 0.0001), after adjusting for above variables. Substantialvariation in Hgb values exists at all GFR levels. These findings underscore the importance of evaluating Hgb atall GFR levels, and the need to study the impact of modificationof Hgb at different GFR levels on survival.     

Disproportional impact of the revised AIDS surveillance definition on the AIDS incidence among drug users compared to homosexual men

The impact of changes in 1993 of the old 1987 WHO/CDC AIDS casedefinition was studied in a cohort of 153 HIV-infected injectiondrug users (IDUs) and 502 HIV-infected homosexual men in Amsterdam.It appeared that the extension in Europe of the old AIDS definitionto also include recurrent pneumonia, pulmonary tuberculosisand invasive cervical neoplasia, strongly increases the numberof persons diagnosed with AIDS among IDUs, but will hardly influencethe AIDS incidence among homosexual men. As recurrent pneumoniaand pulmonary tuberculosis are present among drug users withhigh CD4 cell counts, the incidence of these diseases may partlybe determined by environmental factors. The extension of theold 1987 AIDS definition in the USA with CD4 count <200 cells/mm³In addition to the 3 above-mentioned diseases, will also havea larger impact on drug users than on homosexual men.     

A retrospective mortality study of workers exposed to arsenic in a gold mine and refinery in France

A historical mortality study of a cohort of employees of a gold mining and refining company was carried out in Salsigne, France. A major goal of the study was to investigate the relationship between lung cancer mortality and exposure to arsenic, radon, silica, and other contaminants of the working environment. A twofold excess of lung cancer was found both among miners and smelters, mainly concentrated among workers who had experienced exposure to past levels of arsenic, radon, and silica. The consistency of the results in the mine and the refinery are suggestive of a carcinogenic risk from both soluble and insoluble arsenic, although the potential role of other factors cannot be dismissed. © 1994 Wiley-Liss, Inc.     

Effects of Spascupreel versus hyoscine butylbromide for gastrointestinal cramps in children

BACKGROUND: Gastrointestinal spasms and cramps are common in children as well as in adults. Alternative medical practices such as chiropractice and homeopathy are becoming increasingly popular in Europe and the USA. The effectiveness and tolerability of the homeopathic preparation Spascupreel was compared with that of hyoscine butylbromide treatment in children <12 years of age. METHODS: An observational cohort study in 204 children <12 years was conducted over a 1 week treatment period. The efficacy of the respective therapies were evaluated on the effect on severity of spasms and clinical symptoms (pain/cramps, sleep disturbances, distress, eating or drinking difficulties and frequent crying). Compliance was evaluated on a four-point scale from 'very good' to 'low'. Evaluation was done by the practitioner based on information given by the patient or minder. RESULTS: The analysis showed comparative improvements with the homeopathic preparation and hyoscine butylbromide therapy on severity of spasms, pain/cramps, sleep disturbances, eating or drinking difficulties, and frequent crying, all as evaluated by the practitioner. Both treatments were very well tolerated. CONCLUSIONS: For patients opting for a homeopathic therapy, Spascupreel seems to be an effective and well tolerated alternative to conventional therapies in children suffering from gastrointestinal spasms.     

南阳市1999～2001年新生儿破伤风疫情监测

目的 对南阳市3年的新生儿破伤风疫情监测结果进行分析，掌握该市新生儿破伤风发病概况，有针对地制订防治对策。方法 对3年的监测资料进行分析评价。结果 1999—2001年3年的发病率分别为0．09‰、0．07‰、0．04‰，发病县3年的年发病率均小于1‰。结论 开展各种形式的宣传活动，提倡住院分娩，推广消毒接生，对育龄妇女进行破伤风类毒素接种，从而有效降低其发病率。