Asthma hospitalizations continue to decrease in schoolchildren but hospitalization rates for wheezing illnesses remain high in young children

AIM

To analyse changes in hospitalization rates for asthma in children during recent years.

METHODS

In a population-based analysis, changes in asthma hospitalization rates were studied in children in Göteborg (Gothenburg), the second largest city in Sweden, during 1985-2000. The changes in different age groups have been correlated with the delivery of inhaled corticosteroids to the age groups.

RESULTS

In the 5 to 18-y age group, there was a continuous, significant decrease in number of hospital days, admissions and individual patients admitted for asthma not only for the entire study period, 1985-2000, but also during the past 10-y period. The number of hospital days in the year 2000 was only 6% of the figure for 1985. An inverse correlation between delivery of inhaled corticosteroids and hospitalization for asthma was seen not only during 1985-1995, when use of inhaled corticosteroids became widespread (r(s) = -0.95, p = 0.007 for hospital days), but also when the entire period from 1985 to 2000 was analysed. Conversely, in the 0 to 1-y and 2 to 4-y age groups, there was no decrease in hospitalizations for wheezing illnesses or asthma-like symptoms during the past 10-y period, 1991-2000.

CONCLUSION

During the period 1985-2000 the number of hospital days owing to asthma decreased by more than 90% in the 5 to 18-y age group. The marked decrease in asthma hospitalization rates among schoolchildren represents a great advance in paediatric respiratory medicine, which has been continuous during the past 10-y period. However, in young children admissions for wheezing have apparently not decreased.

Born small for gestational age: relation to future allergy and asthma

AIM

To evaluate whether intrauterine growth retardation (IUGR) protects against the development of allergy.

METHODS

A case-control study of 1515 subjects (15-25 y), of whom 430 were cases (birthweight/length below -2 SD for gestational age). Birth data were from the national birth register. The frequencies of allergic diseases were evaluated by questionnaire.

RESULTS

For the 950 who replied, the frequencies of allergic diseases were similar in cases and controls.

CONCLUSION

IUGR does not protect against the development of allergy.

Bradycardic response during submersion in infant swimming

The diving response involves reflex bradycardia, apnoea and peripheral vasoconstriction and is known to exist in human infants. The response diminishes with increasing age and has been reported to disappear by the age of 6 mo. This study was performed to analyse the physiological events during natural diving of full-term healthy infants and describe how these events alter with maturation. Thirty-six infants were studied during diving exercises in infant swimming. All of the infants who participated showed an immediate decrease in heart rate when submerged. On average, the heart rate decreased by 25% (range -5.0% to -50.7%, p <0.0001). The bradycardia was sustained during the dive and for some seconds afterwards. The response was often followed by a tachycardia as the bradycardia ceased. A decline of reflex bradycardia was observed with increasing age (p = 0.03), but the response was still clearly evident in infants over the age of 6 mo.

CONCLUSION

This study demonstrates the existence of a diving response in infants, which includes an immediate bradycardic response, suggesting vagal mediation. Although the bradycardic response gradually decreases, the study shows that a clear-cut response exists in children older than has previously been reported.

Breast feeding and the sudden infant death syndrome in Scandinavia, 1992-95

AIMS

To assess the effects of breast feeding habits on sudden infant death syndrome (SIDS).

METHODS

The analyses are based on data from the Nordic Epidemiological SIDS Study, a case-control study in which parents of SIDS victims in the Scandinavian countries between 1 September 1992 and 31 August 1995 were invited to participate, each with parents of four matched controls. The odds ratios presented were computed by conditional logistic regression analysis.

RESULTS

After adjustment for smoking during pregnancy, paternal employment, sleeping position, and age of the infant, the adjusted odds ratio (95% CI) was 5.1 (2.3 to 11.2) if the infant was exclusively breast fed for less than four weeks, 3.7 (1.6 to 8.4) for 4-7 weeks, 1.6 (0.7 to 3.6) for 8-11 weeks, and 2.8 (1.2 to 6.8) for 12-15 weeks, with exclusive breast feeding over 16 weeks as the reference. Mixed feeding in the first week post partum did not increase the risk.

CONCLUSIONS

The study is supportive of a weak relation between breast feeding and SIDS reduction.

Relationship between respiratory syncytial virus bronchiolitis and future obstructive airway diseases

Evidence from a large number of prospective case-control studies shows that respiratory syncytial virus (RSV) bronchiolitis in infancy is often associated with recurrent wheezing and asthma during subsequent years. However, wheezing tends to diminish and most studies show no significant increase in wheezing compared to controls by school age or adolescence. An unresolved question is whether severe RSV infection during infancy causes the respiratory sequelae or inherent abnormalities predispose an infant to develop severe respiratory infection and sequelae, i.e. RSV is associated with the development of pulmonary sequelae. Studies on long-term outcome of RSV bronchiolitis are reviewed from an evidence-based perspective. The majority of prospective placebo-controlled studies do not show any long-term beneficial effects of corticosteroid treatment, i.e. the risk of subsequent wheezing is not diminished by the treatment. The evidence for an increased risk of allergic sensitization after RSV bronchiolitis is not nearly as strong as the evidence for an increased risk of subsequent wheezing. In fact, most studies do not show any significant increase in atopy after RSV bronchiolitis. This suggests that the increased risk of wheezing after RSV is not linked to an increased risk of atopy. There are some indications that infants who develop severe RSV and subsequent wheezing may have aberrations that predate the RSV infection. To decide whether respiratory syncytial virus bronchiolitis causes, or is associated with the respiratory sequelae (or with subsequent allergy), it will be necessary to conduct prospective, randomized studies, where the cytokine profile prior to bronchiolitis onset is known. Such studies should preferably include some form of intervention against respiratory syncytial virus. A more complete understanding of the risk factors for severe respiratory syncytial virus infection and the role of respiratory syncytial virus infection in the initiation of asthma is needed as a basis for large-scale and cost-effective programmes to prevent respiratory syncytial virus-related morbidity.

Changes in the epidemiology of sudden infant death syndrome in Sweden 1973-1996

BACKGROUND

From the early 1970s to the early 1990s, there was a significant rise in the incidence of sudden infant death syndrome (SIDS) in Scandinavia. Following the risk reducing campaign, the incidence has fallen to about the same level as in 1973.

AIMS

To identify the changes that have occurred in the epidemiology of SIDS.

METHODS

We compared the Swedish part of the Nordic Epidemiological SIDS Study (NESS), covering the years 1992-1995, with two earlier, descriptive studies during this period. To assess the changing effects of risk factors, we analysed data from the Medical Birth Registry of Sweden, covering the years 1973-1996.

RESULTS

There was a predominance of deaths during weekends in the 1970s and 1990s. The seasonal variation was most notable in the 1980s. The proportion of young mothers decreased from 14% to 5%. Cohabitation (living with the biological father) was as frequent in the 1990s as in the 1970s. The prevalence of high parity, admissions to neonatal wards, low birth weight, prematurity, and multiple pregnancies were all increased in the 1990s compared to the 1970s. No significant change in the prevalence of previous apparent life threatening events was found. Deaths occurring in cars diminished from 10% to below 2%. In the data from the Medical Birth Registry of Sweden, there were significantly increased odds ratios after the risk reducing campaign of the risk factors smoking during early pregnancy and preterm birth. We could find no increased effects of maternal age, parity, or being small for gestational age over time. The rate of deaths at weekends remained increased; the median age at death fell from 90 to 60 days. Seasonal variation was less notable in the periods of low incidence.

Inflammatory mediators in blood and urine

Inflammation plays a major role in the pathophysiology of asthma. Therefore, monitoring of the disease and its management preferably should include assessment of mediators of airways inflammation. Much interest has been focused on using eosinophil granule proteins in blood and urine as markers of asthma inflammation. The eosinophil granule proteins are important mediators in allergic inflammation. They often function well as inflammatory markers when used in controlled clinical studies, and are therefore useful research tools. With urinary eosinophil-derived protein X (EPX) venous blood sampling is avoided. Disadvantages which limit usefulness in clinical practice are overlap between values in patients and controls, a rather weak correlation to traditional lung function variables, elevation of levels by concurrent allergic disease, and the delay between sampling and test results. Urinary excretion of leukotriene E4 (LTE(4)) reflects the production of cysteinyl leukotrienes, which are major mediators in asthma. The excretion of LTE4 possibly reflects lung function better than serum ECP. In the future, monitoring of cytokines may be used in clinical asthma to monitor control and aid in the prognosis of the disease in the young child. Techniques for simple and rapid monitoring of key type 1 and type 2 cytokines are needed.

Topical steroid treatment of allergic rhinitis decreases nasal fluid TH2 cytokines, eosinophils, eosinophil cationic protein, and IgE but has no significant effect on IFN-gamma, IL-1beta, TNF-alpha, or neutrophils

BACKGROUND

Topical treatment with glucocorticoids (GCs) is known to decrease eosinophils but not neutrophils in patients with allergic rhinitis.

OBJECTIVE

We sought to examine whether the differential effects of GC treatment on eosinophils and neutrophils are mirrored by differential effects on T(H)1/T(H)2 cytokines and the neutrophil-associated cytokines IL-1beta and TNF-alpha.

METHODS

Differential counts of eosinophils and neutrophils in nasal fluids from 60 children with seasonal allergic rhinitis treated with a topical GC were examined after staining with May-Grünwald-Giemsa stain. Nasal fluid levels of IFN-gamma, IL-4, IL-6, IL-10, IL-1beta, and TNF-alpha were examined with ELISA, and IgE and eosinophil cationic protein (ECP) levels were examined with RIA.

RESULTS

After GC treatment, there was a statistically significant decrease of the T(H)2 cytokines IL-4, IL-6, and IL-10, as well as ECP and IgE. By contrast, there were no significant changes of the levels of IFN-gamma, IL-1beta, TNF-alpha, or neutrophils. In the GC-treated patients IL-1beta and TNF-alpha levels correlated with neutrophils and ECP, and IL-1beta correlated with eosinophils. Furthermore, ECP correlated with both eosinophils and neutrophils. Neither IL-1beta nor TNF-alpha correlated with IgE. Patients with high neutrophil counts after GC treatment were found to have significantly higher eosinophil counts and ECP than patients with low counts.

CONCLUSIONS

The beneficial effects of topical treatment with GC in patients with allergic rhinitis could be attributed to downregulation of T(H)2 cytokines, with an ensuing decrease of eosinophils, ECP, and IgE. It is possible that neutrophils could counteract the beneficial effects of GCs by releasing the proinflammatory cytokines IL-1beta and TNF-alpha.

Increase of the soluble IL-4 receptor (IL-4sR) and positive correlation between IL-4sR and IgE in nasal fluids from school children with allergic rhinitis

Soluble cytokine receptors (SCR) can either act as inhibitors, by competitively inhibiting cytokines from binding to their membrane-bound receptors, or as enhancers, by serving as cytokine carriers. We have previously found that the levels of the Th2 cytokines interleukin (IL)-4, IL-5, IL-6, and IL-10 were positively correlated to eosinophils and IgE in nasal fluids from 60 children with seasonal allergic rhinitis. In this study, nasal fluids were reexamined to analyze IL-4sR, IL-6sR, IL-1 beta, TNF-alpha, IL-1sR2, TNF-sR1, and TNFsR2 in relation to eosinophils, neutrophils, ECP, and IgE. In allergic patients IL-4sR increased significantly during the pollen season, and weak, but positive correlations with IgE and eosinophils were found (r = 0.45, P < 0.001 and r = 0.4, P < 0.001 respectively). By contrast, none of the other SCR showed increases or correlations with IgE. However, positive correlations between IL1 beta, TNF-alpha, IL-6sR, IL-1sR2, TNF-sR1, TNF-sR2, and either neutrophils or ECP were found. Also, in healthy controls, these cytokines and their receptors were positively correlated to neutrophils or ECP. Thus, increased levels of the soluble IL-4 receptor, as well as IgE, were specifically associated with allergic rhinitis, whereas all other SCR correlated with either inflammatory cells or their products, in both allergic and healthy subjects. These results may suggest that SCR in vivo act as cytokine enhancers, rather than inhibitors.

Low levels of interferon-gamma in nasal fluid accompany raised levels of T-helper 2 cytokines in children with ongoing allergic rhinitis

The T-helper 2 (Th2) cytokines interleukin-(IL-) 4, IL-5, IL-6, IL-10 and the Th1 cytokine IFN-gamma and their associations with eosinophil, eosinophil cationic protein (ECP) and immunoglobulin (Ig) E were studied in nasal lavage fluid from 60 school children with allergic seasonal rhinitis and 36 nonatopic healthy controls, before and during the pollen season. Eosinophil differential counts and IgE increased significantly in the patients during the pollen season. The eosinophil differential counts, ECP and IgE were all significantly higher during the season than in specimens simultaneously obtained from the nonatopic controls. Before season, the levels of ECP and IgE, but not eosinophils, were significantly higher in the patients than in the controls. During the season the nasal lavage fluid levels of IFN-gamma were significantly lower and the IL-4/IFN-gamma quotients significantly higher in the allergic than in the control children. In the allergic children, but not in the controls, the nasal fluid levels of the Th2 cytokines IL-4, IL-5 and IL-10 increased during the season, and together with IL-6, were correlated with the differential counts of eosinophils, and with the levels of ECP and IgE. These findings are compatible with the hypothesis that a deficient release of the Th1 cytokine IFN-gamma plays an important role in the pathogenesis of allergic inflammation. Regardless of whether the defective IFN-gamma secretion is primary or a consequence of suppression by other cytokines, it will in the atopic subjects enhance the release of Th2 cytokines, which in turn will facilitate the development of allergic inflammation.

Living conditions in early infancy in Denmark, Norway and Sweden 1992-95: results from the Nordic Epidemiological SIDS study

The objective was to study living conditions of infants and their families in Scandinavia in the 1990s and to assess similarities and differences among the three Scandinavian countries. The emphasis is on health and normality rather than on diseases and other deviations from well-being. The subjects are the 869 controls in the Nordic Epidemiological SIDS study carried out between 1 September 1992 and 31 August 1995 in Norway, Denmark and Sweden. The controls were matched with the 244 SIDS cases for sex, age and maternity hospital. Parents of the SIDS cases and the controls filled in the same questionnaire on family, pregnancy, delivery, the neonatal and the post-perinatal period. The most striking findings were that 99% of the mothers went to regular maternity controls, 97% to well-baby clinics and 84% breastfed exclusively. On the other hand, 11% drank alcohol more than once a month during pregnancy and 29% smoked during pregnancy. Compared to official statistics, to the extent they exist, the differences were small. The material contains valuable information on normal infant care in Scandinavia in the 1990s. Living conditions of infants in Scandinavia are similar in the three countries. Differences exist, but only to a small extent.

Caffeine and alcohol as risk factors for sudden infant death syndrome. Nordic Epidemiological SIDS Study

OBJECTIVE

To assess whether alcohol and caffeine are independent risk factors for sudden infant death syndrome (SIDS).

MATERIALS AND METHODS

Analyses based on data from the Nordic epidemiological SIDS study, a case control study in which all parents of SIDS victims in the Nordic countries from 1 September 1992 to 31 August 1995 were invited to participate with parents of four controls, matched for sex and age at death. Odds ratios (ORs) were calculated by conditional logistic regression analysis.

RESULTS

The crude ORs for caffeine consumption > 800 mg/24 hours both during and after pregnancy were significantly raised: 3.9 (95% confidence interval (CI), 1.9 to 8.1) and 3.1 (95% CI, 1.5 to 6.3), respectively. However, after adjustment for maternal smoking in 1st trimester, maternal age, education and parity, no significant effect of caffeine during or after pregnancy remained. For maternal or paternal alcohol use, no significant risk increase was found after adjusting for social variables, except for heavy postnatal intake of alcohol by the mother, where the risk was significantly increased.

CONCLUSIONS

Caffeine during or after pregnancy was not found to be an independent risk factor for SIDS after adjustment for maternal age, education, parity, and smoking during pregnancy. Heavy postnatal but not prenatal intake of alcohol by the mother increased the risk.

Interleukin-5 and interleukin-8 in relation to eosinophils and neutrophils in nasal fluids from school children with seasonal allergic rhinitis

The objectives of this study were to measure interleukins 5 and 8 (IL-5 and IL-8) in relation to eosinophils and neutrophils, in nasal lavage fluids from 60 school children with allergic rhinitis, and to determine the influence of treatment with a topical steroid (budesonide) on the levels of the two cytokines. Highly sensitive enzyme immunoassays were used to analyze IL-5 and IL-8. IL-5 levels and relative eosinophil counts in nasal lavage fluid increased significantly in patients with allergic rhinitis during the pollen season, compared with values obtained before the start of the season, and decreased significantly after treatment with budesonide. By contrast, no significant changes in IL-8 or neutrophils were found during the pollen season, nor did they decrease following treatment. In the untreated patients, IL-5 levels correlated significantly with eosinophil counts but not with neutrophil counts, whereas IL-8 levels correlated with neutrophil counts but not with eosinophil counts. After budesonide treatment, the correlation between IL-8 and neutrophils remained, and a correlation between IL-8 and eosinophils emerged. These findings support the concepts that IL-5 has a key role in regulating eosinophils and that IL-8 is important for the regulation of neutrophils. Whereas IL-5 and relative eosinophil counts are profoundly affected by topical steroid treatment, IL-8 and neutrophils are not demonstrably affected by such treatment. It is possible that neutrophils, through the release of IL-8, could be chemotactic for eosinophils in steroid-treated patients.

Interactions of infectious symptoms and modifiable risk factors in sudden infant death syndrome. The Nordic Epidemiological SIDS study

The aim of the study was to investigate the effect of infection on sudden infant death syndrome (SIDS) and to analyse whether modifiable risk factors of SIDS, prone sleeping, covered head and smoking act as effect modifiers. In a consecutive multicentre case-control study of SIDS in Denmark, Norway and Sweden, questionnaires on potential risk factors for SIDS were completed by parents of SIDS victims, and for at least two controls matched for gender, age and place of birth. All SIDS cases were verified by an autopsy. The study comprised 244 SIDS cases and 869 controls, analysed by conditional logistic regression. Significantly more cases than controls presenting symptoms of infectious diseases during the last week and/or last day were treated with antibiotics and had been seen by a physician. The finding is consistent with the hypothesis of an infectious mechanism in SIDS induced by local microorganism growth and toxin or cytokine production, and also adds further support to a possible association between infection and SIDS by loss of protective mechanisms, such as arousal. The risk of SIDS among infants with the combined presence of infectious symptoms and either of the other modifiable risk factors, prone sleeping, head covered or parental smoking, was far greater than the sum of each individual factor. These risk factors thus modify the dangerousness of infection in infancy.

Histamine provocation in young, awake children with bronchial asthma, using a fall in oxygenation as the only indicator of a bronchial reaction

Bronchial provocation with histamine was performed in 11 boys and 6 girls, age range 2.7-7.4 y, with unspecific respiratory symptoms or bronchial asthma, using a fall in oxygenation as the only indicator of a bronchial reaction. In addition to transcutaneous oxygen tension (tcPO2), transcutaneous carbon dioxide tension (tcPCO2) was continuously monitored during the provocation procedure in order to identify possible changes in ventilation. A fall of 20% or more in the tcPO2 below a "floating" baseline value, defined as the highest tcPO2 value between the inhalations of histamine up to that point, was regarded as indicating a significant bronchial reaction. One child was excluded from the study because of an "early, false-positive" reaction due to hyperventilation during the inhalation, verified by a decrease in the tcPCO2 followed by a compensatory period of hypoventilation, resulting in a fall of more than 15% in the tcPO2 after the inhalation of saline. In the vast majority of the children, however, the tcPO2 values remained stable during the first dose stages of saline and histamine, with either a gradual fall immediately before or a distinct fall in conjunction with the reaction. The mean reaction concentration was significantly lower in the group of children with clinical asthma, 0.74 mg/ml, compared with the group of children with unspecific respiratory symptoms, 2.00 mg/ml (p = 0.03). In conclusion, a 20% fall in the tcPO2 can be used as the only indicator of a bronchial reaction during bronchial provocation tests in young, awake children. Changes in ventilation evaluated by monitoring tcPCO2, makes it possible to distinguish between a fall in oxygen tension due to an early, "false" reaction as a result of hypoventilation and a "true" bronchial reaction.

Short- and long-term efficacy. Childhood asthma

In clinical studies of asthma, great attention should be focused on the choice and validation of outcome measures. The outcome parameters to be used when evaluating efficacy of early intervention in childhood asthma treatment must be closely linked to the aims of the intervention and considered in the design of the study. In an interventional study, possible adverse consequences should also be considered as outcome measures when designing the study. The appropriate time span for assessing different types of interventions may vary from days to several decades, depending on the character of the intervention. Not only outcome parameters, such as improvement in symptom score and improvement of lung function, but also those that measure reduction in frequency and severity of acute exacerbations, reduction in morbidity and improvement in quality of life should be used. For some purposes, a more detailed approach to symptom severity is needed, such as separation of acute from chronic symptoms. Other outcome measures that need to be considered are: cost-effectiveness, normalization of inflammatory changes in the airways, control of airway hyperresponsiveness, airway growth and prevention of airway remodelling and importantly, whether an intervention against asthma can alter the natural course, or cure, the disease. Interventions should be evaluated to see to what extent such aims have been met.

A case-control study of smoking and sudden infant death syndrome in the Scandinavian countries, 1992 to 1995. The Nordic Epidemiological SIDS Study

AIM

To establish whether smoking is an independent risk factor for sudden infant death syndrome (SIDS), if the effect is mainly due to prenatal or postnatal smoking, and the effect of smoking cessation.

METHODS

The analyses were based on data from the Nordic epidemiological SIDS study, a case-control study with 244 cases and 869 controls. Odds ratios were computed by conditional logistic regression analysis.

RESULTS

Smoking emerged as an independent risk factor for SIDS, and the effect was mainly mediated through maternal smoking in pregnancy (crude odds ratio 4.0 (95% confidence interval 2.9 to 5.6)). Maternal smoking showed a marked dose-response relation. There was no effect of paternal smoking if the mother did not smoke. Stopping or even reducing smoking was beneficial. SIDS cases exposed to tobacco smoke were breast fed for a shorter time than non-exposed cases, and feeding difficulties were also more common.

CONCLUSIONS

Smoking is an independent risk factor for SIDS and is mainly mediated through maternal smoking during pregnancy. Stopping smoking or smoking less may be beneficial in reducing the risk of SIDS.

Prevalence of allergy in children in relation to prior BCG vaccination and infection with atypical mycobacteria

By influence on the Th1/Th2 cell balance, infectious agents may affect the development of atopic allergy. In this study, we investigated whether previous BCG vaccination or infection with atypical mycobacteria might be related to the development of atopic disease. The study, which involved skin testing with mycobacteria and answers to a questionnaire for more than 6000 children in Sweden, revealed a low prevalence of allergy among BCG-vaccinated children who were immigrants or adopted from other countries. Vaccinated children born in Sweden, however, did not have significantly lower allergy prevalence than age-matched, unvaccinated children. Furthermore, the overall frequencies of skin-test reactivity to the atypical mycobacteria M. avium and M. scrofulaceum were higher rather than lower in allergic than in nonallergic children. By contrast, there was a tendency toward a lower frequency of more strongly positive skin reactions (> or = 10 mm) to mycobacteria in allergic than in nonallergic children. These findings do not support the hypothesis that early mycobacterial infections have a suppressive effect on the development of atopic disease. Earlier findings of an apparent association between atopy and lack of previous mycobacterial infection may possibly be explained by a relatively decreased ability of atopic patients to mount strong Th1 cell-mediated immune responses.

Sociodemographic risk factors for sudden infant death syndrome: associations with other risk factors. The Nordic Epidemiological SIDS Study

The aim of this study was to investigate associations between sudden infant death syndrome (SIDS) and social factors in the Nordic countries. A case-control study was conducted in Denmark, Norway and Sweden: The Nordic Epidemiological SIDS Study. Parents of 244 SIDS infants and 869 control infants matched on gender, age at death and place of birth filled in questionnaires. The dataset was analysed by conditional logistic regression. In univariate analysis, the following sociodemographic factors were associated with an increased risk of SIDS: low maternal age [odds ratio (OR) 7.8; 2.8-21.5], high birth order (OR 4.4; 2.5-7.5), single motherhood (OR 2.9; 1.7-5.0), low maternal education (OR 4.5; 2.8-7.1), low paternal education (OR 3.0; 1.9-4.7), maternal unemployment (OR 2.4; 1.8-3.4) and paternal unemployment (OR 4.0; 2.7-5.9). In a multivariate analysis where maternal smoking was also included, only paternal unemployment, young maternal age and high birth order remained significantly associated with SIDS. Housing conditions were not associated with SIDS. However, the risk of SIDS was high if the family had lived in their present home for only a few years (OR 2.3; 1.3-4.1). Sociodemographic differences remain a major concern in SIDS in a low-incidence situation and even in an affluent population with adequate health services.