The concentration of particulate matter in outdoor air, as indicated by daily measures of particulate matter 10 microm in diameter (PM10) in many cities, has been found to be associated with the daily number of deaths and hospital admissions in these cities. To understand this association better, we studied the daily number of hospital admissions for respiratory diseases and the concentrations of eight pollutants in ambient air, during a period of 38 months, in an area with cold winters and air pollution that comes mainly from motor vehicles. We estimated the changes in risk of hospitalization by interquartile increases in pollutant concentrations by Poisson regression analyses. Controlling for periodic trends and weather, the relative risk of hospitalization associated with an interquartile increase of PM10 was 1.038 [95% confidence interval (CI) = 0.991-1.087]. In contrast, the relative risk associated with benzene was 1.105 (95% CI = 1.047-1.166). In a two-pollutant model, the relative risk estimates were 1.014 (95% CI = 0.966-1.063) for PM10 and 1.090 (95% CI = 1.031-1.153) for benzene. We evaluated other two- and three-pollutant models and concluded that pollutants other than PM10 are more strongly associated with hospital admissions for respiratory diseases.
The objective of the study was to assess the relationship between breastfeeding and lower respiratory tract infections (LRTIs) during the first year of life, with special reference to maternal smoking. A cohort of 3,754 children born in 1992-1993 in the City of Oslo, Norway was recruited and data were collected at birth, 6 and 12 months of age. Complete information was obtained from 3,238 children (follow-up rate 86%). The main outcome was an episode of a LRTI, such as pneumonia, bronchitis or bronchiolitis, based on a self-administered questionnaire addressed to parents when the child was 6 and 12 months old. The outcome was specified as physician-diagnosed. In logistic regression analysis adjusting for confounding, maternal smoking increased the risk of LRTIs in children breastfed for 0-6 months (odds ratio (AOR) 1.7; 95% confidence interval (95% CI) 1.2-2.4), but not essentially when the child was breastfed for more than 6 months (AOR 1.1; 95% CI 0.7-1.6). Short-term breastfeeding (0-6 months) and no maternal smoking was related to an adjusted AOR of LRTIs of 1.3 (95% CI 1.0-1.7), and short-term breastfeeding combined with maternal smoking was related to an adjusted AOR of 2.2 (95% CI 1.6-3.1), as compared with long-term breastfeeding and no maternal smoking. The present study indicates a protective effect of long-term breastfeeding on the risk of lower respiratory tract infection during the first year of life. The results suggest that the protective effect is strongest in children exposed to environmental tobacco smoke.
OBJECTIVE: To estimate the effects of the type of day care on respiratory health in preschool children. METHODS: A population-based cross-sectional study of Oslo children born in 1992 was conducted at the end of 1996. A self-administered questionnaire inquired about day care arrangements, children's health, environmental conditions, and family characteristics (n = 3853; response rate, 79%). RESULTS: In logistic regression controlling for confounding, children in day care centers had more often nightly cough (adjusted odds ratio, 1.89; 95% confidence interval, 1.34-2. 67), and blocked or runny nose without common cold (1.55; 1.07-1.61) during the past 12 months compared with children in home care. Poisson regression analysis showed an increased risk of the common cold (incidence rate ratio, 1.21; 1.12-1.30) and otitis media (1.48; 1.22-1.80), and the attributable proportion was 17.4% (95% confidence interval, 10.7-23.1) for the common cold and 32.4% (18. 0-44.4) for otitis media. Early starting age in the day care center increased the risk of developing recurrent otitis media. Also the lifetime risk of doctor-diagnosed asthma was higher in children who started day care center attendance during the first 2 years of life. CONCLUSIONS: Attendance to day care centers increases the risk of upper respiratory symptoms and infections in 3- to 5-year-old children. The starting age seems to be an important determinant of recurrent otitis media as well as asthma. The effect of day care center attendance on asthma is limited to age up to 2 years. This effect is most likely mediated via early respiratory tract infections that are substantially more common in children in day care centers compared with children in home care.
In this study the impact of pregnancy duration on the measured level of HSV-2 antibodies was assessed. The study population comprised 35,940 pregnant women in Norway, in 1992-4, followed during pregnancy. A random sample of 960 women was selected. A mean of 2.6 serum samples from each woman were analysed for HSV-2 specific IgG antibodies at different times in pregnancy. Crude and adjusted odds ratios were estimated in logistic regression models taking all observations per women into account. Twenty-seven percent of the pregnant women had antibodies against HSV-2 in the first trimester. The adjusted odds ratio of being HSV-2 antibody positive decreased during the pregnancy and was 0.5 (0.2-0.9, 95% confidence interval) in the 40th as compared to the 10th week of pregnancy. About 50% of initially HSV-2 positive women did not have detecable antibodies by the end of the pregnancy. This may be explained by haemodilution during pregnancy. Our findings have diagnostic implications and should encourage further studies.
BACKGROUND: Fetuses of women who repeat small-for-gestational-age births in successive pregnancies may have a different intrauterine growth pattern than SGA birth of non-repeater mothers. Also repeated SGA births may grow differently depending on whether the tendency to repeat is due to some external factors such as cigarette smoking ("false repeaters") or due to genetic or intrinsic factors ("true repeaters"). MATERIAL AND METHODS: Fetal growth were compared in a "nested case-control" study within a longitudinal (cohort) study, comparing three types of SGA births, 23 of "true repeater" mothers, 46 of "false repeater" mothers and 65 of non-repeater mothers, and these were compared with 1017 non-SGA births. Fetal growth was compared using a regression analysis based on repeated measurements (four for each woman). RESULTS: For mean abdominal diameter the "true repeater" SGA births grew more slowly towards the end of pregnancy. However, the growth curves show only minor differences between the three types of SGA births, but the patterns are grossly different from the growth of non-SGA births (controls). CONCLUSION: The intrauterine growth retardation starts early in pregnancy, and is not strikingly different between births of repeater and non-repeater mothers.
In order to assess the relationship between recurrent acute otitis media (rAOM) and age at first acute otitis media (AOM) episode, a prospective cohort of 3754 Norwegian children born in 1992-1993 was followed from birth to 2 years. Recurrent acute otitis media was defined by the criterion of four or more episodes of AOM during a 12-month period. Approximately 5.4% of the children experienced rAOM before the age of 2. Furthermore, children whose first AOM episode occurred before the age of 9 months were at a significantly higher risk for developing rAOM compared to children whose first AOM episode was 10-12 months. In children who had the first ear infection during the first 9 months of life, one-quarter developed rAOM before the age of 2. Multiple logistic regression analysis adjusted for confounding showed that gender and a familial history of atopy were significantly associated with rAOM. In conclusion, the present study found an association between age at first AOM episode and the later subsequent AOM proneness. Additionally, both gender and a family history of atopy seemed to predispose towards otitis-proneness.
We assessed the effect of exposure to environmental tobacco smoke on the risk of developing bronchial obstruction in a 2-year cohort study of 3,754 children born in Oslo, Norway, during a period of 15 months in 1992-1993. We collected questionnaire information on the child's health and environmental exposures at birth and when the child was age 6 months (follow up rate = 95%), 12 months (92%), 18 months (92%), and 24 months (81%). The outcome of interest was defined as two or more episodes of bronchial obstruction or one obstruction lasting more than 1 month, and it was verified by a specialist group evaluating data from questionnaires, clinical examinations, and health records. The risk of bronchial obstruction was increased in children exposed to environmental tobacco smoke (cumulative incidence = 0.109) compared with unexposed children (0.071), with an adjusted odds ratio of 1.6 [95% confidence interval (CI) = 1.3-2.1]. The effect was seen for maternal smoking alone (odds ratio = 1.6; 95% CI = 1.0-2.6), paternal smoking alone (odds ratio = 1.5; 95% CI = 1.1-2.2), and both parents smoking (odds ratio = 1.5; 95% CI = 1.0-2.2). There was no clear exposure-response pattern. The findings indicate that exposure to environmental tobacco smoke such as is experienced in Norwegian housing increases the risk of developing bronchial obstruction during the first 2 years of life.
OBJECTIVE: To assess the weight gain during the first year of life in relation to maternal smoking during pregnancy and the duration of breastfeeding. DESIGN: This was a one year cohort study. SETTING: The city of Oslo, Norway. PARTICIPANTS: Altogether 3020 children born in Oslo in 1992-93. Children were divided into three groups as follows: 2208 born to non-smoking mothers, 451 to mothers who were light smokers ( or = 10 cigarettes per day). MAIN RESULTS: The mean birth weights were 3616 g, 3526 g, and 3382 g and 1 year body weights were 10,056 g (gain 6440 g per year), 10,141 g (6615 g), and 10,158 g (6776 g) in children of non-smoking and light and heavy smoking mothers respectively. Cox regression analysis showed that children of heavy smokers were 2.0 (95% confidence interval, 1.7, 2.3) times and children of light smokers 1.3 (1.2, 1.5) times more likely to have stopped breast feeding during their first year of life compared with children whose mothers were non-smokers. Linear regression analysis, adjusting for confounders, showed that weight gain was slower in breast fed children than in those who were not breast fed (-38 g (-50, -27) per month of breast feeding). Compared with children of non-smokers, the adjusted weight gain was 147 g (40, 255) per year greater in children of light smokers and 184 g (44, 324) per year in children of heavy smokers. CONCLUSION: Children catch up any losses in birth weight due to maternal smoking, but some of the catch up effect is caused by a shorter duration of breast feeding in children of smoking mothers.
Comment In: J Epidemiol Community Health. 1999 Apr;53(4):25610396556