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OBJECTIVES: Bottle-feeding has been suggested to increase the risk of pyloric stenosis (PS). However, large population-based studies are needed. We examined the effect of bottle-feeding during the first 4 months after birth, by using detailed data about the timing of first exposure to bottle-feeding and extensive confounder information. METHODS: We performed a large population-based cohort study based on the Danish National Birth Cohort, which provided information on infants and feeding practice. Information about surgery for PS was obtained from the Danish National Patient Register. The association between bottle-feeding and the risk of PS was evaluated by hazard ratios (HRs) estimated in a Cox regression model, adjusting for possible confounders. RESULTS: Among 70 148 singleton infants, 65 infants had surgery for PS, of which 29 were bottle-fed before PS diagnosis. The overall HR of PS for bottle-fed infants compared with not bottle-fed infants was 4.62 (95% confidence interval [CI]: 2.78–7.65). Among bottle-fed infants, risk increases were similar for infants both breast and bottle-fed (HR: 3.36 [95% CI: 1.60–7.03]), formerly breastfed (HR: 5.38 [95% CI: 2.88–10.06]), and never breastfed (HR: 6.32 [95% CI: 2.45–16.26]) (P = .76). The increased risk of PS among bottle-fed infants was observed even after 30 days since first exposure to bottle-feeding and did not vary with age at first exposure to bottle-feeding. CONCLUSIONS: Bottle-fed infants experienced a 4.6-fold higher risk of PS compared with infants who were not bottle-fed. The result adds to the evidence supporting the advantage of exclusive breastfeeding in the first months after birth.

OBJECTIVE: The risk of infantile hypertrophk pylonc stenosis is ∼5 times more common in male than female infants. It has been hypothesized that the higher risk among male infants is associated with high levels of testosterone causing hypertrophy of the pylorus muscle. To test this hypothesis, we examined the association between the testosterone levels in the umbilical-cord blood and the risk of infantile hypertrophic pyloric stenosis. PATIENTS AND METHODS: We conducted a matched case-control study nested in the Danish National Birth Cohort using risk-set sampling. From a cohort of 101 042 pregnancies, we identified umbilical-cord blood samples from 46 case subjects (43 male and 3 female infants) who developed infantile hypertrophic pyloric stenosis in the first year of life and 150 gender- and gestational age–matched control subjects. The testosterone levels were measured by liquid chromatography–tandem mass spectrometry. Rate ratios were estimated by using conditional logistic regression. RESULTS: In male infants, the mean testosterone level at birth was 0.78 nmol/L in case subjects and 0.91 nmol/L in control subjects. The rate of infantile hypertrophic pyloric stenosis was inversely, albeit insignificantly, associated with the testosterone levels in male infants; there was a 29% (95% confidence interval: −46% to 65%; P = 35) lower rate per nmol/L. The association was not modified according to age, gestational age, or birth order. CONCLUSIONS: We found no support for the hypothesis that high testosterone levels in the umbilical-cord blood are strongly associated with a subsequently higher risk for infantile hypertrophic pyloric stenosis in male infants.

OBJECTIVE. The risk of invasive pneumococcal disease is increased among children with some chronic diseases. The objective of this study was to quantify the risk of invasive pneumococcal disease in a wide range of chronic diseases. PATIENTS AND METHODS. Cases of invasive pneumococcal disease among children (aged 0–17 years) were identified from 1977 through 2005 by using a national surveillance program in Denmark. Rate ratios were assessed in a case-control study by using 10 age- and gender-matched controls per case. Chronic diseases were defined a priori. RESULTS. Among 1655 children with invasive pneumococcal disease, 19% had a history of chronic disease, according to our definition, versus 5% of controls. An increased risk of invasive pneumococcal disease was observed for children followed >30 days after initial hospital contact for a chronic disease, but it was also increased in children with ≥5 hospital contacts for any other reason. Children with a history of cancer, chronic renal disease, splenectomy, and transplantation were particularly susceptible to invasive pneumococcal disease. Adjusted for number of hospital contacts, the risk for children with other types of chronic disease was 1.4-fold more than for those with hospital contacts for any reason. CONCLUSIONS. Cancer, chronic renal diseases, splenectomy, and transplantation were strongly associated with an increased risk of invasive pneumococcal disease in children. For children with other chronic diseases, their excess risk seemed to be attributable mostly to frail children having repeated hospital contact rather than their underlying condition.

OBJECTIVES. It is well known that children attending childcare have a higher risk of acute respiratory infections compared with children in home care; however, knowledge is sparse regarding how the excess risk of acute respiratory infection varies with age, time since enrollment, and other factors.METHODS. A national register-based study of 138821 inpatient admissions to hospital for acute respiratory infection during 3982925 person-years of follow-up in Danish children aged 0 to 5 years. Data on child and family characteristics, childcare attendance, and hospitalizations were obtained from Danish registries. The outcome of the study was inpatient admissions to hospital for acute respiratory infection. Incidence rate ratios were estimated using Poisson regression.RESULTS. In children CONCLUSIONS. The increased risk of acute respiratory infection was most pronounced among 0- to 2-year-old children living with no other children during the first 6 months of enrollment. Our findings may suggest that it would be optimal to postpone enrollment into childcare until after 1 year of age.

Objective. To describe incidence and temporal trends of intussusceptions in Danish children during 1980 to 2001. Methods. A population-based cohort study was conducted of 1.67 million children who were younger than 5 years during 1980 to 2001 and were followed up for 6.66 million person-years. The Danish National Patient Registry was used to identify cases of intussusception in the cohort. Age-specific incidence rates were main outcome measure. Results. A total of 1814 cases of intussusception among children who were younger than 5 years were reported from 1980 to 2001. The incidence rate remained fairly constant during 1980 to 1990 but decreased by 55% (95% confidence interval: 43%–65%) from 1990 to 2001. The reduction was most pronounced among children aged 3 to 5 months. Conclusions. The incidence of intussusception among Danish children declined significantly during the 1990s, particularly among infants 3 to 5 months of age.