Computer modelling of the Swedish two county trial of mammographic screening and trade offs between participation and screening interval.

OBJECTIVES: A computerised model of the Swedish two county trial of mammographic screening was built to explore the applicability of deterministic group modelling for health policy analysis and to examine trade offs between screening interval and population coverage on breast cancer mortality. METHODS: Powersim system dynamics modelling software running on a PC was used. Model inputs were published data on the populations and screening regimens used in the trial, a Swedish female population life table, incidence of breast cancer in Sweden, 95% confidence intervals (95% CIs) for mean sojourn time and screening sensitivity, and survival after diagnosis. RESULTS: The model's output--cumulative mortality from breast cancer--agreed closely with trial results. This was robust to uncertainties in key input variables. Furthermore, with hypothetical screening regimes that had a fixed total number of mammograms over a fixed period a positive association was found between more even distribution of mammograms among a population and reduction in breast cancer mortality. For example, screening 50% of a hypothetical population annually produced a 33% reduction in breast cancer mortality, whereas screening 100% of the population every 2 years produced a 48% reduction. CONCLUSIONS: Deterministic group simulation modelling can be used to build reliable, evidence based quantitative models for policy analysis. This opens health policy simulation modelling to epidemiological researchers and will assist them in identifying important information needs--such as breast cancer survival according to sojourn time (the time between cancer being detectable by screening and becoming symptomatic). Scenarios examining reductions in mortality for a given number of mammograms showed that the more equitable the distribution of screening mammograms, the greater the reduction in deaths from breast cancer.

Serological survey of measles and rubella immunity in Sydney preschool children.

OBJECTIVES: To estimate the prevalence of serological evidence of immunity to measles and rubella in preschool children in central and southern Sydney (NSW, Australia) and the prevalence of immunity in children with either documented or parentally reported immunization. METHODS: Geographical cluster random sampling was used to select children aged between 18 and 60 months to participate in the present study. Standardized interviews obtained information on each child's reported (by parents) immunization status and documentary evidence of immunization was recorded from the Personal Health Record. Venous blood was collected, serum was separated and stored frozen until tested. Measles and rubella antibodies were measured using ELISA, with either immunofluorescence or haemagglutination inhibition being used to clarify equivocal results. The study was conducted from 1992 to 1994 in conjunction with surveys of blood lead concentrations, iron status and micronutrient status. RESULTS: Parents of 726 of 953 children identified between 9 and 60 months of age agreed to participate in the lead, immunization, iron status and micronutrient studies. Sufficient blood for antibody testing was obtained from 580 children, aged 18 to 62 months at the time of collection. Parents reported that 94.7% (95% confidence interval (CI) 92.7-96.5%) of children had received a measles-mumps or measles-mumps-rubella (MMR) immunization. General practitioners administered 72.8% of these immunizations. The prevalence of serological evidence of immunity to measles and rubella was 88.8% (95% CI 86.2-91.4%) and 91.9% (95% CI 89.6-94.2%). respectively. There was documented evidence of measles and rubella immunization for 88.4% (95% CI 85.7-91.2%) and 86.4% (95% CI 83.4-89.3%) of children, respectively. Of children with documented measles immunization, 91.6% (95% CI 89.2-94.0%) had detectable measles antibody. Of children with documented rubella immunization 97.2% (95% CI 95.8-98.6%) had detectable rubella antibody. CONCLUSIONS: Measles and rubella immunization rates in central and southern Sydney are relatively high and most of these immunizations are provided by the private sector. Immunity to rubella in children with documented rubella immunization is at the level that would be expected from seroconversion studies. Immunity to measles in children with documented measles immunization is slightly lower than expected from seroconversion studies, highlighting the need for the second MMR immunization in preschool children, as well as making near universal immunization imperative if this disease is to be eradicated.

Plasma and serum micronutrient concentrations in preschool children.

The plasma concentrations of vitamin A, vitamin E, beta-carotene and serum concentrations of zinc, retinol-binding protein and prealbumin were examined for a random cluster sample, stratified by socioeconomic status, of 467 healthy preschool children. Children were aged 9-62 months; 44% were females. The mean plasma values were: vitamin A, 1.29 micromol l(-1); vitamin E, 18.9 micromol l(-1); and beta-carotene, 0.30 micromol l(-1). The mean serum values were: zinc, 13.9 micromol l(-1); retinol-binding protein, 25.5 mg l(-1); and prealbumin, 186.2 mg l(-1). The mean molar ratio of vitamin A to retinol-binding protein for the study group was 1.10. There were no differences in the mean values of any of the measured micronutrients between the genders. The results of this survey do not indicate that the prevalence of micronutrient deficiency in this preschool population is of public health significance.

Infection control and contaminated waste disposal practices in Southern Sydney Area Health Service Dental Clinics.

The sterilization and contaminated waste disposal practices in all 14 dental clinics operated by the Southern Sydney Area Health Service were surveyed. All of the clinics used autoclaves for sterilization. All hand instruments, handpieces and triplex syringes were autoclaved between patients. Chemical disinfection solutions were used in 12 of the 14 dental clinics, mainly for surface decontamination. Five dental clinics had separate storage areas for contaminated waste which compiled with contaminated waste separation and disposal guidelines. The practice of recapping needles with fingers and some inadequate washing facilities are areas that require particular attention.

Age-specific reference intervals for plasma vitamins A, E and beta-carotene and for serum zinc, retinol-binding protein and prealbumin for Sydney children aged 9-62 months.

Paediatric reference intervals for blood concentrations of certain nutrients are often based on either adult data or are derived from small samples of young children. Biochemical data were obtained from 467 randomly selected, healthy preschool children aged 9-62 months in Sydney, Australia. Data were obtained for plasma vitamins A, E and beta-carotene and for serum zinc, retinol-binding protein and prealbumin. Reference intervals based on the 2.5 and 97.5 centiles for age groups 9-23, 24-35, 36-47, 48-62 months and for the total group (9-62 months) were calculated. The 2.5-97.5 centiles for the whole group were: vitamin A, 0.7-1.8 mumol/l (20.05-51.56 micrograms/dl); vitamin E, 8-30 mumol/l (0.34-1.29 mg/dl); beta-carotene, 0.1-1.1 mumol/l (5.4-59.0 micrograms/dl); zinc, 9-19 mumol/l (58.8-124.2 micrograms/dl); retinol-binding protein, 14-36 mg/l; prealbumin, 104-264 mg/l. The reference intervals reported are consistent with the findings of a number of smaller studies and are likely to be an accurate reflection of the true intervals for healthy preschool children in western developed countries.

Iron status and anaemia in preschool children in Sydney.

The purpose of this study was to determine the iron status of preschool children in Sydney. We assessed 678 children aged 9 to 62 months living in 32 randomly selected census collection districts in central and southern Sydney for iron status using plasma ferritin; of these 678 children, 542 had zinc protoporphyrin tests, red cell indices and haemoglobin tests. Risk factors for iron deficiency were assessed by an administered questionnaire. Overall, the prevalence of iron depletion was 10.5 per cent, iron deficiency 2.8 per cent and iron deficiency anaemia 1.1 per cent. The 24-to-35-month age group (176 children) had the highest prevalence of iron deficiency anaemia of 3.0 per cent although iron depletion (18.7 per cent) and iron deficiency (5.4 per cent) were highest among the 9-to-23-month age group (182 children). Low iron status was related to age of under 24 months (odds ratio (OR) 2.86,95 per cent confidence interval (CI) 1.72 to 4.76). After adjustment for this age effect, the consumption of red meat fewer than four times a week was significantly associated with iron depletion (OR 2.27, CI 1.25 to 4.17) and there was a tendency for children who were being given a vitamin supplement to be less likely to be iron depleted (OR 4.00, CI 0.95 to 16.67). Iron deficiency and iron deficiency anaemia do not represent a major public health problem in preschool children in Sydney. However, for children in the age range of 12 to 36 months there is scope for interventions to further reduce the prevalence of iron deficiency anaemia.

Prevalence of tuberculosis infection among primary school-entry children in Sydney.

A cross-sectional survey of 2044 Year I children enrolled in 24 primary schools was performed to determine the prevalence of tuberculosis (TB) infection. Of the 2044 children, 1458 (71 per cent) were Mantoux-tested and 1452 Mantoux reactions were read. Of the total, 6.5 per cent were Mantoux-positive; 17.8 per cent of overseas-born children and 2.8 per cent of Australian-born children were Mantoux-positive (relative risk for overseas-born 6.9, 95 per cent confidence interval 4.2 to 9.6). In the areas of Sydney where the study was conducted, there is a high prevalence of TB infection (non-contagious) among overseas-born children in the five- to seven-year age group. This indicates that there may be a large pool of infected children, a proportion of whom are at risk of developing active (contagious) adult-type TB in the future. These data, with other published data on TB infection rates in other age groups, can contribute to the estimation of the size of the infected pool in Australia to allow rational decisions regarding control of TB in Australia, including the possibility of introducing Mantoux screening and preventive therapy programs for high-risk groups.

Blood lead concentrations of preschool children in central and southern Sydney.

OBJECTIVES: To determine the prevalence of elevated blood lead concentrations in preschool children in central and southern Sydney. PARTICIPANTS AND SETTING: Children aged from 9 months to 5 years living in 32 randomly selected geographical areas in Central and southern Sydney. METHODS: Venous blood lead concentrations were estimated by atomic absorption spectrometry. RESULTS: 953 children were identified and 726 had parental consent to participate. A blood sample for lead estimation was obtained from 718 children. The geometric mean blood level concentration was 0.34 mu mol/L (7.0 mu/dL). The proportion of children with elevated blood lead concentrations was: 16.1% (>0.48 mu mol/L [10mu/dL]), 3.9% (>0.72 mu mol/L[15mu/dL]) and 0.3% (>1.21mu mol/L [25 mu/dL], respectively. The blood lead levels for children living with a 10-km radius of the Sydney Central Business district were: 25% (>0.48 mu mol/L [10mu/dL]) and 7% (>0.72 mu mol/L [15mu/dL]), respectively. Corresponding findings for children living 10 km outside this radius were: 9% (>0.48 mu mol/L [10mu/dL]) and 1.5% (0.72 mu mol/L [15mu/dL]), respectively. CONCLUSIONS: The proportion of children with elevated blood lead concentrations in Central and Southern Sydney as a whole does not exceed current National Health and Medical Research Council (NHMRC) recommendations. However, in those areas within a 10-km radius of the Central Business District, NHMRC interventional guidelines for communities where more that 5% of children have blood lead concentrations higher than 0.72 mu mol/L (15 mu/dL) should be applied.

The prevalence of tuberculosis infection among Year 8 schoolchildren in inner Sydney in 1992.

OBJECTIVE: To determine the prevalence of tuberculosis (TB) infection in Year 8 schoolchildren (aged 12-14 years) in Sydney. DESIGN: Cross-sectional survey. SETTING: 22 inner city Sydney secondary schools. PARTICIPANTS: 2290 Year 8 school children enrolled in 1992. OUTCOME MEASURES: Distribution of Mantoux test reaction size and proportion of children who were Mantoux positive (i.e., having Mantoux reaction > or = 15 mm with previous Bacille Calmette-Guérin vaccination; > or = 10 mm without). RESULTS: Of the 2290 children, 1836 (81%) were screened and 1801 Mantoux reactions were read. Ten per cent of children were Mantoux positive--27% of foreign-born children and 2% of Australian-born children (relative risk 16.7, 95% confidence interval 10.6-26.4). Two children were found to have active TB disease. CONCLUSION: There is a high prevalence of primary (non-contagious) TB infection in children aged 12-14 years in inner Sydney, mostly confined to children born overseas. Thus there is a large pool of infected children at risk of developing active (contagious) adult-type TB disease in the future. This public health problem should be addressed by identification and treatment of those infected.

Community prevalence survey of children's blood lead levels and environmental lead contamination in inner Sydney.

OBJECTIVE: To determine the distribution of blood lead levels in preschool children in inner Sydney and identify possible sources of environmental lead. DESIGN: Cross sectional community based prevalence survey of children and the houses in which they live, and a survey of volunteer children. SETTING: Mort Bay and Summer Hill, residential localities in inner Sydney. PARTICIPANTS: Ninety-five children aged 9-48 months able to be identified in a defined geographic area and 63 children aged 9-48 months volunteered by their parents. OUTCOME MEASURES: Concentrations of lead in venous blood of all children and in samples from the home environment of Mort Bay children. RESULTS: Four of the children (2.5%) had blood lead levels > or = 1.21 mumol/L (25 micrograms/dL, the current Australian threshold of concern), 27 (17.1%) had levels > or = 0.72 mumol/L (15 micrograms/dL, the new US threshold for individual intervention) and 80 (50.6%) had levels > or = 0.48 mumol/L (10 micrograms/dL, the new US threshold for community intervention). Blood lead concentrations were significantly correlated with concentrations of lead in "sink" soil (r = 0.555, P = 0.026), play area soil (r = 0.492, P = 0.016) and dust from vacuum cleaners (r = 0.428, P = 0.05), and with age of child (r = -0.182, P = 0.023). The presence of the child during house renovation was a strong predictor of having a blood lead level above 0.72 mumol/L (15 micrograms/dL) (odds ratio, 4.6; 95% confidence interval, 1.8-11.7, P = 0.001). CONCLUSIONS: Lead in soil and in household dust in older areas of Sydney is likely to represent a significant health hazard to young children. Many thousands of children may be affected in Sydney and other Australian cities. There is an urgent need for expanded prevalence surveys, public education and the development of strategies for the abatement of lead in urban environments.

Mortality among Australian conscripts of the Vietnam conflict era. I. Death from all causes.

A retrospective cohort study of mortality was conducted to assess whether Army service of young Australian men in the Vietnam conflict influenced the subsequent risk of premature death. Analysis related to all National Servicemen (generally conscripts in the Australian Army) who enlisted during the conflict and served in the Army for at least 12 months. Of these veterans, 19,205 served in Vietnam, while 25,677 served only in Australia. All men were traced from the end of their national service engagement (between 1966 and 1976) until January, 1, 1982. For both groups, death rates were statistically significantly lower than expected for Australian males of the same age. Overall mortality of Vietnam veterans was 1.3 times that of non-Vietnam veterans (95% confidence interval (Cl) = 1.1-1.5). After adjustment for the confounding effects of Army corps grouping, Vietnam veteran mortality was 1.2 times that of non-Vietnam veterans (95% Cl = 1.0-1.4). No other variable examined was confounding. The excess of deaths among Vietnam veterans relative to the veterans not serving in Vietnam was largely confined to The Royal Australian Engineers. Among members of this corps, the relative mortality rate was 2.5 (95% Cl = 1.4-4).

Mortality among Australian conscripts of the Vietnam conflict era. II. Causes of death.

In a cohort of Australian national service conscripts, death rates from International Classification of Diseases, Eighth Revision (ICD-8) cause of death classes for 19,205 veterans of the Vietnam conflict were compared with those of 25,677 veterans who served only in Australia. Comprehensive, clinically reviewed cause of death data were collected and coded to a single ICD-8 three-digit cause of death code by the Australian Bureau of Statistics. Over 98% of the deaths among veterans were included in five classes of causes of death. These were neoplasms (14%), diseases of the circulatory system (7%), accidents, poisonings, and violence (external causes) (74%), and diseases of the digestive system and mental disorders (2% each). For the last two classes, chronic abuse of alcohol was a common factor in most deaths among Vietnam veterans. The death rates of Vietnam veterans were statistically significantly higher than those for other veterans for only two classes of causes of death: diseases of the digestive system and external causes. After adjustment for Army corps grouping, this excess was not statistically significant for external causes. There was no statistically significant difference in death rates from neoplasms, nor were deaths from specific neoplasms more frequent among the group that served in Vietnam. While this suggests that service in the Vietnam conflict has not increased death rates from neoplasms among servicemen, the follow-up period, ranging from 9-16 years, is shorter than the latency period for some neoplasms. The study findings provide a measure of support for claims by Australian Vietnam veterans of an increased incidence of stress-related disorders associated with service in the Vietnam conflict.

Mortality among Vietnam veterans compared with non-veterans and the Australian population.

A retrospective cohort study of mortality was conducted to assess whether the military service of young Australian men in Vietnam has influenced their overall death rates, or those from specific causes. The study was of all national servicemen who were conscripted during the conflict and served in the Army for at least 12 months. Of these, 19 205 served in Vietnam (veterans) while 25 677 served only in Australia (non-veterans). These men were traced from the end of their national service (between 1966 and 1973) until the beginning of 1982. For most causes of death, the observed number of deaths of veterans and of non-veterans was less than expected from Australian population death rates, and for no cause was there a statistically significant excess of deaths compared with that of the Australian population. Similarly, when veterans were compared with non-veterans, there was no statistically significant difference in deaths for all causes combined, for diseases of the circulatory system, for deaths in motor vehicle accidents, for suicide and for all external causes after adjustment for the different subsequent death rates of men who had served in different Army corps. All seven deaths from diseases of the digestive system were of veterans. There was no excess of deaths among veterans from cancer or from atypical causes of death in this group of young men. Three-quarters of deaths of both veterans and non-veterans were from external causes, often involving motor vehicle accidents.

Measuring the accuracy of vital status data in cohort studies.

To measure the quality of vital status data in a retrospective cohort study of mortality among former servicemen of the Vietnam Conflict era, test subjects of independently determined vital status were included among study subjects during vital status ascertainment procedures. This allowed for differentiation between vital status "unknown" and incorrect assignment of vital status, and enabled measurement of the quality of both live and deceased vital status data. Four parameters based on sensitivity and specificity were used to express the quality of vital status data. The deceased specificity rate was 100 per cent, the deceased sensitivity rate was 95.7 per cent, the live specificity rate was 98.5 per cent, and the live sensitivity rate was 95.4 per cent. Using models of misclassification, the estimated death rate was found to be most sensitive to changes in the deceased specificity rate, indicating that emphasis should be given to minimizing incorrect ascertainment of truly alive subjects as deceased when developing vital status ascertainment procedures.