Effect of infection control measures on the frequency of upper respiratory infection in child care: a randomized, controlled trial.

BACKGROUND: Acute upper respiratory infections are common in children who attend child care, and preventing transmission of disease in this setting depends on actions by child care staff. We set out to discover whether transmission of respiratory infections in child care could be reduced by improved infection control procedures. METHODS: We performed a cluster, randomized, controlled trial of an infection control intervention conducted in child care centers in 1 city in Australia. The intervention was training of child care staff about transmission of infection, handwashing, and aseptic nosewiping technique. Implementation of the intervention was recorded by an observer. Illness was measured by parent report in telephone interviews every 2 weeks. RESULTS: There were 311 child-years of surveillance for respiratory symptoms. By multivariable analysis, there was no significant reduction in colds in intervention center children across the full age range. However, a significant reduction in respiratory illness was present in children 24 months of age and younger. When compliance with infection control practices was high, colds in these children were reduced by 17%. CONCLUSIONS: This trial supports the role of direct transmission of colds in young children in child care. The ability of infection control techniques to reduce episodes of colds in children in child care was limited to children 24 months of age and under.

Effect of infection control measures on the frequency of diarrheal episodes in child care: a randomized, controlled trial.

BACKGROUND: Diarrheal infections are common in children who attend child care, and preventing transmission of disease in this setting depends on actions by child care staff. We set out to discover whether transmission of gastrointestinal infections in child care could be reduced by improved infection control procedures. METHODS: We performed a cluster randomized, controlled trial of an infection control intervention conducted in child care centers for 1 city in Australia. The intervention was training of child care staff about transmission of infection and handwashing and focused on both staff and child behavior. Implementation of the intervention was recorded by an observer. Illness was measured by parent report in telephone interviews every 2 weeks. RESULTS: There were 311 child-years of surveillance for diarrheal episodes. The rate of episodes of diarrhea was 1.9 per child-year in intervention centers and 2.7 per child-year in control centers. Multivariable analysis showed that diarrheal episodes were significantly reduced in intervention center children by 50%. However, the impact of the intervention was confined to children over 24 months of age. For those centers in which children's compliance with handwashing was high, diarrheal episodes were reduced by 66%. CONCLUSIONS: This trial supports education about infection control, for staff and children in child care, as a means of reducing transmission of diarrhea. Reduction in episodes of diarrhea in children in child care was limited to children over 24 months of age.

ML and REML estimation in survival analysis with time dependent correlated frailty.

In the study of multiple failure times for the same subjects, for example, recurrent infections for patients with a given disease, there are often subject effects, that is, subjects have different risks that cannot be explained by known covariates. Standard methods, which ignore subject effects, lead to overestimation of precision. The frailty model for subject effects is better, but can be insufficient, because it assumes that subject effects are constant over time. Experience has shown that the dependence between different time periods often decreases with distance in time. Such a model is presented here, assuming that the frailty is no longer constant, but time varying, with one value for each spell. The main example is a first-order autoregressive process. This is applied to a data set of 128 patients with chronic granulomatous disease (CGD), participating in a placebo controlled randomized trial of gamma interferon (gamma-IFN), suffering between 0 and 7 infections. It is shown that the time varying frailty model gives a significantly better fit than the constant frailty model.

Threshold models in a methadone programme evaluation.

The degree of non-compliance with a methadone programme is such that a zero is often recorded as the response variable. Such outcome variables cannot be transformed to normality in order to investigate a regression relationship between the response variable and various risk or treatment variables. The presence of a random effect as well in this regression causes added difficulty in the analysis. We show here that use of threshold models can provide a satisfactory solution to both these problems.

Trends in the prevalence of trachoma, South Australia, 1976 to 1990.

The eye health of rural Aboriginal Australians is known to be poor. Over the past 20 years, Aboriginal communities in remote parts of Australia have had increasing access to eye health services through the National Trachoma and Eye Health Program (NTEHP). Using published and unpublished data, we examined trends in the prevalence of inflammatory trachoma in the Anangu Pitjantjatjara of South Australia. Comparisons using a generalised linear model of surveys in 1976, 1985 and 1990 indicate that there has been a significant reduction in the age-standardised prevalence of inflammatory trachoma in 0- to 20-year-olds. When the 1990 survey was compared with 1976 interim report data from the NTEHP survey, the odds of inflammatory trachoma in 1990 were 0.25 (95 per cent confidence interval (CI) 0.18 to 0.35). When the comparison was with data from the NTEHP survey of the Red Centre, the odds of follicular trachoma in 1990 were 0.51 (CI 0.42 to 0.62), and in comparison with the 1985 NTEHP review data, the odds of inflammatory trachoma in 1990 were 0.28 (CI 0.20 to 0.39). In the older age groups (20 and over), an increase in the prevalence of inflammatory trachoma was found. Although significant, the increase affected a small proportion of the population and may have been because of difficulty in standardising the trachoma grading between surveys, or systematic grading error in the 1990 survey. This study therefore shows that the eye health of Aboriginal people in Central Australia may be improving. The decline in trachoma is welcome and may be caused by improvements in socioeconomic conditions, community development and increasing access to medical care.

Sequential continuity of care by general practitioners: which patients change doctor?

OBJECTIVE: To identify individual and social characteristics of patients making sequential visits to a different rather than the same general practitioner (GP). METHOD: Data for this study were extracted from the "Record Linkage Pilot Study" of the National Centre for Epidemiology and Population Health, which linked information from personal interviews with Health Insurance Commission and National Heart Foundation Risk Factor Survey data. Each sequence of visits (any two consecutive visits) made by each participant to the same or a different GP from January 1991 to December 1992 was treated as an event. PARTICIPANTS: 521 subjects aged between 23 and 72 years who gave consent to release of Health Insurance Commission data. MAIN OUTCOME MEASURE: A visit to the same GP or a different GP from the one seen at the last visit. RESULTS: Logistic regression analysis showed that younger age, good physical functioning, good self-rated health, normal body mass index, shiftwork and a longer time interval between visits were significantly associated with less continuity of care. CONCLUSIONS: Our study raises questions about the relationship between chronological continuity and quality of care. For example, if infrequent visits (associated with less continuity) are for distinct illnesses, is quality of care affected by information or treatment from a previous visit? Our results also suggest that some GPs, because of the demography of their practices (more young people, a higher proportion of shift workers), may be disadvantaged by continuity-based reward systems. Moreover, because of lack of continuity young people may miss out on GPs' health promotional activities.

Loglinear models using capture-recapture methods to estimate the size of a measles epidemic.

Cases of measles reported separately by doctors, hospitals, laboratories, and others are treated as separate captures and releases of the population of children aged up to 10 years who have been infected by measles in a recent epidemic. Loglinear models are used to assess the adequacy of fit of various models for capture-recapture and the size of the epidemic in different age groups is estimated.

Survival analysis and prognosis for dementia patients.

How long a dementia patient is cared for in the home before admission to a nursing home depends on the state of the patient and the state of the caregiver. Using 5-year follow-up data, the times until entry to nursing home and until death are modeled using a Cox survival model in which patient and caregiver variables at entry to study as well as changes in these variables over the following 12 months are the regression variables. Treatment variables quantify the effects of a caregiver training program. Statistical methods used in fitting the Cox survival model and consequent predictions of survival rates are discussed.

Time until institutionalization and death in patients with dementia. Role of caregiver training and risk factors.

OBJECTIVE: To determine which variables best predict prognosis--time to nursing home admission (NHA) and death--in patients with dementia. DESIGN: Survival analysis employing the Cox proportional hazards model with the use of risk variables pertaining to dementia severity and its rate of progression and caregiver functioning. SETTING: Patients and their caregivers participating in a controlled intervention study of training for caregivers in home management of dementia. PARTICIPANTS: Patients with mild Diagnostic and Statistical Manual of Mental Disorders, Third Edition--defined dementia (N = 91; 68 patients with Alzheimer-type dementia, 20 with vascular dementia, and three with other types) and their caregivers. FOLLOW-UP: All subjects had repeated assessments in the first year to determine rates of change and thereafter annually to determine the date of NHA and/or death. RISK VARIABLES: (1) Caregiver training; (2) dementia severity at index assessment; (3) caregiver stress, neuroticism, and socialization; (4) changes in patients and caregivers during the first 12 months; and (5) patient characteristics. RESULTS: By 5 years' follow-up, 76% of patients had entered a nursing home and 42% had died. Dementia severity and rate of deterioration ("how far" and "how fast") and caregiver psychological morbidity significantly influenced rates of NHA and death. Training of caregivers was significantly associated with delayed NHA and reduced mortality. Greater patient age, non-Alzheimer's dementia, and, unexpectedly, greater caregiver psychological morbidity were associated with shorter survival to death. CONCLUSIONS: Both severity ("how far") and rate of deterioration ("how fast") influence time to NHA and death. Caregiver training may have important ameliorating effects on the prognosis of dementia.

REML estimation for survival models with frailty.

A method of estimation for generalised mixed models is applied to the estimation of regression parameters in proportional hazards models for failure times when there are repeated observations of failure on each subject. The subject effect is incorporated into the model as a random frailty term. Best linear unbiased predictors are used as an initial step in the computation of maximum likelihood and residual maximum likelihood estimates.

Variance components for discordances.

Tests for biotyping isolates give a result that is classified as either positive or negative, indicative of growth or nongrowth of bacteria. The reproducibility of such tests is measured by the number of discordances in replicates of the same measurement. In this analysis the probability distribution of the number of discordances is estimated for each of several tests in the presence of possible random between-laboratory effects as well as random laboratory-test interactions, which are also estimated.

Percutaneous aortic valvuloplasty.

OBJECTIVE: To determine the short-term and long-term results of percutaneous aortic valvuloplasty. DESIGN: A retrospective follow-up study. SETTING: The Cardiac Catheterisation Laboratory and Cardiovascular Medicine Unit of a teaching hospital. PATIENTS: Eighteen patients with severe aortic stenosis who were not accepted for surgery; there were 11 men and 7 women, mean age 79 +/- 4.5 years. INTERVENTIONS: Percutaneous transluminal aortic valvuloplasty (PTAV) by means of balloon catheter techniques. MAIN OUTCOME MEASURES: Patient survival and symptomatic status. RESULTS: PTAV resulted in a significant decrease in the aortic valve pressure gradient from 64.8 +/- 23.2 mmHg to 38 +/- 14.7 mmHg (mean +/- SD) (P less than 0.00001) in the 18 patients and a significant increase in the mean aortic valve area from 0.4 +/- 0.16 cm2 to 0.6 +/- 0.18 cm2 (P less than 0.0001) in 14 patients. Complications occurred in seven patients; two of them, who had been in terminal heart failure with a low output state before PTAV, died. Fifteen patients improved in at least one New York Heart Association functional class early after PTAV and one patient had an aortic valve replacement. In follow-up of between 5 and 32 months (mean, 13.3 +/- 7.7 months) six patients are in a better functional class than before PTAV, one patient is in Class IV, one patient had an aortic valve replacement and seven patients died (three died of cardiac failure and four of non-cardiac causes). CONCLUSIONS: PTAV has a place as a palliative procedure in selected patients with aortic stenosis in whom another condition precludes aortic valve replacement.

Regression with frailty in survival analysis.

In studies of survival, the hazard function for each individual may depend on observed risk variables but usually not all such variables are known or measurable. This unknown factor of the hazard function is usually termed the individual heterogeneity or frailty. When survival is time to the occurrence of a particular type of event and more than one such time may be obtained for each individual, frailty is a common factor among such recurrence times. A model including frailty is fitted to such repeated measures of recurrence times.

A model for the analysis of growth data from designed experiments.

A model for growth data from designed experiments is presented which extends the stochastic differential equation of Sandland and McGilchrist (1979, Biometrics 35, 255-272). Residual maximum likelihood (REML) is used to estimate the parameters of the model. The model is easily extended to incomplete data and is shown to overcome some of the practical difficulties encountered with the profile model. The procedure is applied to data from experiments on pigs and sheep.

A Markov transition model in the analysis of the immune response.

A method for the analysis of repeated measures of immune response is given. Typically the reactions of response to stimulus do not occur at the same time for all experimental units so that regression models are inappropriate for this type of data. Instead Markov transition models are suggested and procedures given for testing differences among response patterns.

Environmental Factors Influencing Numbers of Rhizobium leguminosarum biovar trifolii and Its Bacteriophages in Two Field Soils.

Fluctuations in numbers of Rhizobium leguminosarum biovar trifolii and its bacteriophages in two fields with different soil types were followed during a 17-month period in 1981 and 1982. Mean levels of both phage and rhizobia varied significantly (P < 0.05) on different occasions, with rhizobial levels varying from 1.6 x 10 to 2.0 x 10 cell per g of soil and phage from 0 to 1.7 x 10 PFU/g of soil. Multivariate regression analysis showed rhizobial levels to be significantly and positively related to vegetation height and solar radiation, but not to mean temperature, precipitation, soil matric potential, or soil type. Rhizobiophage concentrations were significantly and positively related to soil matric potential and vegetation height. They were reduced in the silty clay loam soil, although the presence of 34% clay did not prevent phage multiplication and the occurrence of high phage levels.

Smoking: a major predictor of left ventricular function after occlusion of the left anterior descending coronary artery.

The major predictors of left ventricular function after coronary artery occlusion were assessed in 108 consecutive patients who had complete occlusion of the left anterior descending artery as the only important lesion demonstrated at angiography between June 1978 and June 1983. A scoring system was used to identify regional damage on left ventriculograms. Forty two patients were classified as having good left ventricular function and 66 as having varying degrees of impairment. Apart from a history of myocardial infarction, the only variables discriminating between those with good and those with impaired left ventricular function were the area of distribution of the artery beyond the occlusion and cigarette smoking. Hypertension, hypercholesterolaemia, family history of vascular disease, diabetes, obesity, duration of angina, age, and presence of identifiable collaterals were not discriminators. Smoking was itself significantly associated with a history of infarction; but after controlling for this, smoking exerted a significant additional effect on the amount of left ventricular damage. It is concluded that smoking is not only a risk factor for myocardial infarction in patients with single left anterior descending artery occlusion, but that it is also a major factor in determining the extent of associated left ventricular damage.

Estimation of cumulative illness using cross-sectional data.

Using cross-sectional data, a general method is given for assessing cumulative illness due to a particular disease. An application is given to estimating cumulative illness due to otitis media in Australian aborigines and contrasting these results to the non-aboriginal population.

The inheritance of serum cholesterol: adjustment of observed cholesterol levels for age, sex and body weight using inverse-polynomial regression.

Adjustment of observed serum cholesterol levels for biological and environmental variables is an essential step in studying the mode of inheritance of serum cholesterol. Body weight, measured as weight/height2, is found to be an important variable not previously taken into account in regression equations. A method is given for adjusting cholesterol levels for age, sex and body weight, thus obtaining residuals which represent the deviations of cholesterol levels from the mean of the general population for each category of these three factors. The procedure for incorporating into the model other variables, that are found to have a significant effect on cholesterol level, is described. Polynomials and inverse polynomials of degree three fit the data equally well over a restricted range. However, inverse polynomials are chosen as they appear to have a more appropriate shape and are likely to agree better with observed values over a greater age range.