Sudden infant death syndrome related to climate

Screening for viral pathogens in the gastrointestinal tract from cases of sudden unexpected death in infancy at the Tygerberg Medico-legal Mortuary

Sudden and unexpected death in infancy (SUDI) may be triggered by an external risk or exposure. Intestinal infections with enteric viruses may disrupt the gut and enhance bacterial toxins present in SUDI cases. While diarrhoeal disease deaths have decreased worldwide, approximately half a million deaths still occur in children in Sub- Saharan Africa and South Asia. Furthermore, the role of viral enteropathogens in SUDI cases have not been investigated. The aim of this study was to describe specific viral pathogens in stool samples collected from SUDI cases and age-matched, apparently healthy infants in Cape Town, South Africa. Stool samples were collected from 176 SUDI cases between June 2017 and May 2018. In addition, stool samples were collected from the nappies of 30 age-matched, apparently healthy infants as a control group. Real-time polymerase chain reaction was performed on the stool samples for viral detection. A total of 111 SUDI cases were positive for viruses, with rotavirus (38.6%; 68/176) and norovirus GI and GII (30.0%; 53/176) were prevalent in SUDI cases. Adenovirus Type F was present in only 15.9% (28/176), astrovirus in 9.7% (17/176), and sapovirus in 0.6% (1/176) of cases. In the control samples, norovirus GII was detected most frequently (36.7%; 11/30), followed by rotavirus (33.3%; 10/30), and sapovirus in 6.7% (2/30). While there was no significant association between SUDI cases and enteric viruses, the majority of viruses were significantly associated with the seasons. The study confirms the importance of rotavirus vaccination and describes the significance of norovirus infection in children, post rotavirus vaccine introduction.

Hyperthermia and Heat Stress as Risk Factors for Sudden Infant Death Syndrome: A Narrative Review

BACKGROUND AND OBJECTIVES

Heat stress and hyperthermia are common findings in sudden infant death syndrome (SIDS) victims. It has been suggested that thermal stress can increase the risk of SIDS directly via lethal hyperthermia or indirectly by altering autonomic functions. Major changes in sleep, thermoregulation, cardiovascular function, and the emergence of circadian functions occur at the age at which the risk of SIDS peaks-explaining the greater vulnerability at this stage of development. Here, we review the literature data on (i) heat stress and hyperthermia as direct risk factors for SIDS, and (ii) the indirect effects of thermal loads on vital physiological functions.

RESULTS

Various situations leading to thermal stress (i.e., outdoors temperatures, thermal insulation from clothing and bedding, the prone position, bed-sharing, and head covering) have been analyzed. Hyperthermia mainly results from excessive clothing and bedding insulation with regard to the ambient thermal conditions. The appropriate amount of clothing and bedding thermal insulation for homeothermia requires further research. The prone position and bed-sharing do not have major thermal impacts; the elevated risk of SIDS in these situations cannot be explained solely by thermal factors. Special attention should be given to brain overheating because of the head's major role in body heat losses, heat production, and autonomic functions. Thermal stress can alter cardiovascular and respiratory functions, which in turn can lead to life-threatening events (e.g., bradycardia, apnea with blood desaturation, and glottal closure). Unfortunately, thermal load impairs the responses to these challenges by reducing chemosensitivity, arousability, and autoresuscitation. As a result, thermal load (even when not lethal directly) can interact detrimentally with vital physiological functions.

CONCLUSIONS

With the exception of excessive thermal insulation (which can lead to lethal hyperthermia), the major risk factors for SIDS appears to be associated with impairments of vital physiological functions when the infant is exposed to thermal stress.

The EASE Project Revisited: Improving Safe Sleep Practices in Ohio Birthing and Children's Hospitals

Literature has shown hospitalized infants are not often observed in recommended safe sleep environments. Our objective was to implement a quality improvement program to improve compliance with appropriate safe sleep practices in both children's and birthing hospitals. Hospitalists from both settings were recruited to join an Ohio American Academy of Pediatrics collaborative to increase admitted infant safe sleep behaviors. Participants used a standardized tool to audit infants' sleep environments. Each site implemented 3 PDSA (Plan-Do-Study-Act) cycles to improve safe sleep behaviors. A total of 37.0% of infants in children's hospitals were observed to follow the current American Academy of Pediatrics recommendations at baseline; compliance improved to 59.6% at the project's end (P < .01). Compliance at birthing centers was 59.3% and increased to 72.5% (P < .01) at the collaborative's conclusion. This study demonstrates that a quality improvement program in different hospital settings can improve safe sleep practices. Infants in birthing centers were more commonly observed in appropriate sleep environments than infants in children's hospitals.

Influence of Skin-to-Skin Contact and Rooming-In on Early Mother–Infant Interaction

The objective of this research was to study influence of birth routines on mother–infant interaction at Day 4. The present research is part of a longitudinal study where mother–infant pairs were randomized by infant location and apparel. We intended to assess mother–infant interaction from videos filmed at Day 4. A protocol for the assessment/coding of the affective quality of maternal behaviors indicative of early mother–infant interaction was developed and interculturally validated. Results were compared with birth randomization, as to explain impact of birth practices. Findings indicate that separation and swaddling at birth interfered with mother–infant interaction during a breastfeeding session at Day 4; these mothers significantly demonstrated more roughness in their behaviors with their infants at Day 4. Results also show evidences of a sensitive period for separation after birth. Implications are to encourage immediate and uninterrupted skin-to-skin contact at birth, and rooming-in during postpartum, as recommended in World Health Organization/UNICEF Ten Steps for Successful Breastfeeding.

Swaddling: a traditional care method rediscovered

BACKGROUND

This study was undertaken to compare the sleep profiles of healthy infants in swaddling and sleeping bag conditions.

METHODS

Polysomnographs of 85 healthy infants (40 in the study group, 45 in the control group) with a mean age of 7.5 weeks were recorded in the sleeping laboratory. A positive decision from the local Ethics Committee and the written consent of the parents were obtained for the study.

RESULTS

Swaddling significantly reduces the rate of spontaneous waking (events/h: 1.39 [0.85-2.77] vs. 2.81 [1.49-4.53], P=0.020) and the number of sleep stage changes (events/h: 3.82 [2.97-5.16] vs. 5.37 [3.58-6.67], P=0.015). Swaddling promotes quiet sleep (36.37% [29%-40.31%] vs. 30.2% [24.45%-36.78%], P=0.032), the time spent awake was decreased (8.98% [4.62%-14.25%] vs. 14.17% [9.2%-18.94%], P=0.001) and sleep efficiency was increased (91.02% [85.75%-95.38%] vs. 85.83% [81.06%-90.8%], P=0.001).

CONCLUSION

Swaddling promotes a more quiet sleep in infants.

Virological investigations in sudden unexpected deaths in infancy (SUDI)

Previous studies have implicated viral infections in the pathogenesis of sudden unexpected death in infancy (SUDI), and routine virological investigations are recommended by current SUDI autopsy protocols. The aim of this study is to determine the role of post-mortem virology in establishing a cause of death. A retrospective review of 546 SUDI autopsies was carried out as part of a larger series of >1,500 consecutive paediatric autopsies performed over a 10-year period, 1996-2005, in a single specialist centre. Virological tests were performed as part of the post-mortem examination in 490 (90%) of the 546 SUDI autopsies, comprising 4,639 individual virological tests, of which 79% were performed on lung tissue samples. Diagnostic methods included immunofluorescence assays (using a routine respiratory virus panel; 98% of cases), cell culture (61%), rapid culture techniques such as the DEAFF test for CMV (55%), PCR (13%), electron microscopy (10%), and others. Virus was identified in only 18 cases (4%), viz. five cases of enterovirus, four of RSV, three of HSV and CMV, and one each of adenovirus, influenza virus and HIV. In seven of the 18 cases the death was classified as due to viral infection, whilst of the remaining 11 cases, death was due to bacterial infection in five, a non-infective cause in one and unexplained in five. Virus was identified in 33% of deaths due to probable viral infections, but also in 6% of SUDI due to bacterial infections, and in 2% of SUDI due to known non-infective causes and unexplained SUDI. When predominantly using immunofluorescence, virus is identified in only a small proportion of SUDI autopsies, resulting in a contribution to the final cause of death in <2% of SUDI post-mortem examinations. Routine post-mortem virological analysis by means of an immunofluorescence respiratory virus panel appears to be of limited benefit in SUDI for the purposes of determining cause of death. Application of a broader panel using more sensitive detection techniques may reveal more viruses, although their contribution to the final cause of death requires further exploration.

Cardiovascular control during sleep in infants: Implications for Sudden Infant Death Syndrome

In infants the cardiorespiratory system undergoes significant functional maturation after birth and these changes are sleep-state dependent. Given the immaturity of these systems it is not surprising that infants are at risk of cardiorespiratory instability, especially during sleep. A failure of cardiovascular control mechanisms in particular is believed to play a role in the final event of Sudden Infant Death Syndrome (SIDS). The "triple risk model" describes SIDS as an event that results from the intersection of three overlapping factors: (1) a vulnerable infant, (2) a critical development period in homeostatic control, and (3) an exogenous stressor. This review summarises normal development of cardiovascular control during sleep in infants and describes the association of impaired cardiovascular control with the three overlapping factors proposed to be involved in SIDS pathogenesis.

Sudden infant death syndrome in Brazil: fact or fancy?

CONTEXT AND OBJECTIVE

The true incidence of sudden infant death syndrome (SIDS) in Brazil is unknown. The aim here was to identify SIDS cases in the city of Ribeirão Preto, State of São Paulo, between 2000 and 2005, in order to estimate its incidence.

DESIGN AND SETTING

Retrospective analysis of data on live births and infant deaths in Ribeirão Preto and from autopsies of infants performed at the Death Verification Service of the Interior (SVOI) between 2000 and 2005.

RESULTS

There were 47,356 live births and 537 deaths, with infant mortality rates ranging from 12.9 to 10.9 of live births. Among the 24 infants who died possibly due to SIDS and who were autopsied at the SVOI, six were from families living in the municipality (0.13 of live births): three (50%) were diagnosed as SIDS, and one each (16.66%) as indeterminate cause, bronchoaspiration and cerebral edema. Two deaths occurred in the first month of life (33.33%) and one each (16.66%) at two, four, six and eight months. Two deaths each (33.33%) occurred in the months of February and December, one each in August and October (16.66%). Four cases (66.7%) occurred in the summer and one each (16.66%) in winter and spring. There was 5:1 predominance of males over females.

CONCLUSIONS

The frequency of SIDS was lower than what has been reported worldwide and in the Brazilian literature, thus suggesting underdiagnosis, indicating the lack of any specific postmortem protocol for SIDS identification and showing the need to implement this.

Swaddling: a systematic review

Swaddling was an almost universal child-care practice before the 18th century. It is still tradition in certain parts of the Middle East and is gaining popularity in the United Kingdom, the United States, and The Netherlands to curb excessive crying. We have systematically reviewed all articles on swaddling to evaluate its possible benefits and disadvantages. In general, swaddled infants arouse less and sleep longer. Preterm infants have shown improved neuromuscular development, less physiologic distress, better motor organization, and more self-regulatory ability when they are swaddled. When compared with massage, excessively crying infants cried less when swaddled, and swaddling can soothe pain in infants. It is supportive in cases of neonatal abstinence syndrome and infants with neonatal cerebral lesions. It can be helpful in regulating temperature but can also cause hyperthermia when misapplied. Another possible adverse effect is an increased risk of the development of hip dysplasia, which is related to swaddling with the legs in extension and adduction. Although swaddling promotes the favorable supine position, the combination of swaddling with prone position increases the risk of sudden infant death syndrome, which makes it necessary to warn parents to stop swaddling if infants attempt to turn. There is some evidence that there is a higher risk of respiratory infections related to the tightness of swaddling. Furthermore, swaddling does not influence rickets onset or bone properties. Swaddling immediately after birth can cause delayed postnatal weight gain under certain conditions, but does not seem to influence breastfeeding parameters.

[Sleeping habits related to sudden infant death syndrome: a population-based study]

This cross-sectional study on sleeping habits with potential risk for sudden infant death syndrome included all live births in Passo Fundo, Rio Grande do Sul, Brazil, in 2003 with data collection from Certificates of Live Birth and interviews, analyzed with descriptive statistics and the chi-squared test. From the 2,634 live births, 2,285 children were selected (86.75%), with 8.4% exclusion and 5.2% losses. Protective habits included 77% of infants with appropriate clothing, 90% loosely wrapped, 69% with thin blankets, 98% sleeping in the parents' bedroom, and 56% in the crib. Potentially risky habits included lateral decubitus (92%), use of a pillow (88%), and feet far from the lower edge of the crib (96%). Among low-income families, bed-sharing with other children was significant (p = 0.00). Thus, in a county with a low prevalence of sudden infant death syndrome, infants are exposed to both protective and risk factors, suggesting that in underprivileged populations in developing countries, other risk factors for this syndrome should be considered.

Heat stress and sudden infant death syndrome incidence: a United States population epidemiologic study

OBJECTIVES

To determine the role of heat stress in sudden infant death syndrome (SIDS) by examining the SIDS rates during periods of extreme environmental temperatures in a period when most infants were placed prone for sleep.

DESIGN

A retrospective study of SIDS rates and mortality rates attributable to excessive environmental heat in relationship to climatologic temperature was performed. Data were collected for each of 454 counties in 4 states (Arkansas, Georgia, Kansas, and Missouri) from May 1 to September 30, 1980, and were then summed to yield the mortality rates for each 5 degrees F (2.8 degrees C) temperature range.

RESULTS

chi2 analyses revealed significant relationships for heat-related mortality rates and both the maximal daily temperature and mean daily temperature but demonstrated no such relationships for SIDS rates. No association between SIDS rates and heat-related mortality rates was found with Spearman's ranked correlation, for either the maximal daily temperature or the mean daily temperature.

CONCLUSIONS

On the basis of our findings of no significant association between SIDS and either measure of temperature during periods of high heat stress-related death rates, it seems unlikely that the heat stress associated with the combination of prone sleep positions and elevated environmental temperatures has a significant role in the development of SIDS.

Viruses and sudden infant death

Viral respiratory infections are the most likely trigger for sudden infant death syndrome (SIDS). SIDS cases commonly have evidence of respiratory tract inflammation, a preceding history of symptoms of minor illness and occur in winter peaks coinciding with respiratory viral epidemics. Respiratory infections are a common cause for infants presenting with sudden events, involving apnoea and hypoxaemia and there are physiological mechanisms by which infants may develop sudden and severe, potentially life-threatening hypoxaemia. The rate of SIDS has fallen in the last 15 years. This is probably more to do with the reasons for the fall in deaths from respiratory causes rather than changes in sleeping position. Further falls in SIDS death rates may occur with reductions in cigarette smoking, encouragement of breastfeeding and minimising the potential for young infants to acquire respiratory infections. Early identification and recognition of life-threatening features of infections may further minimise the risks of sudden death.

Sudden infant death syndrome: overview and update

The past decade and a half has seen marked changes in the epidemiology of sudden infant death syndrome (SIDS). The avoidance of certain risk factors such as sleeping prone and cigarette smoke exposure has resulted in the death rate falling dramatically. Careful evaluation of environmental factors and endogenous characteristics has led to a greater understanding of the complexities of the syndrome. The development and implementation of death scene and autopsy protocols has led to standardization in approaches to unexpected infant deaths with increasing diagnoses of accidental asphyxia. Despite these advances, there is still confusion surrounding the diagnosis, with deaths being attributed to SIDS in many communities and countries where death scene investigations and autopsies have not been conducted. The following review provides a brief overview of the historical background, epidemiology, pathology, and pathogenesis of SIDS. Contentious issues concerning the diagnosis and current problems are discussed. Despite calls to abandon the designation, SIDS remains a viable term for infants who die in their sleep with no evidence of accident, inflicted injury, or organic disease after a full investigation has been conducted according to standard guidelines.

Risks of ancient practices in modern times

Swaddling, ie, wrapping the child to restrict movement, is an ancient practice. In the Netherlands, it is becoming increasingly popular as an intervention for excessive crying in infants. However, one must be well aware of the potential risks. We present the case reports of a twin boy and girl who had been swaddled and kept in a heated room for several days. On admission to the hospital, both infants suffered from severe hypovolemic shock, hyperthermia, and secondary respiratory insufficiency. The girl developed multiple organ dysfunction syndrome and died, whereas the boy had an uneventful recovery. When swaddling is being considered as an intervention for excessive crying in infants, parents have to be well-informed about the possible side effects and about additional measures that they may have to take to make it a safe intervention.

The contribution of prone sleeping position to the racial disparity in sudden infant death syndrome: the Chicago Infant Mortality Study

BACKGROUND

Rates of sudden infant death syndrome (SIDS) are over twice as high among African Americans compared with Caucasians. Little is known, however, about the relationship between prone sleeping, other sleep environment factors, and the risk of SIDS in the United States and how differences in risk factors may account for disparities in mortality.

OBJECTIVE

To assess the contribution of prone sleeping position and other potential risk factors to SIDS risk in a primarily high-risk, urban African American population.

DESIGN, SETTING, AND POPULATION

Case-control study consisting of 260 infants ages birth to 1 year who died of SIDS between November 1993 and April 1996. The control group consists of an equal number of infants matched on race, age, and birth weight. Prospectively collected data from the death scene investigation and a follow-up home interview for case infants were compared with equivalent questions for living control participants to identify risk factors for SIDS.

MAIN OUTCOME MEASURES

Risk of SIDS related to prone sleeping position adjusting for potential confounding variables and other risk factors for SIDS, and comparisons by race-ethnicity.

RESULTS

Three quarters of the SIDS infants were African American. There was more than a twofold increased risk of SIDS associated with being placed prone for last sleep compared with the nonprone positions (odds ratio [OR]: 2.4; 95% confidence interval [CI]: 1.6-3.7). This OR increased after adjusting for potential confounding variables and other sleep environment factors (OR: 4.0; 95% CI: 1.8-8.8). Differences were found for African Americans compared with others (OR: 1.8; 95% CI: 1.2-2.6 and OR: 10.3, 95% CI: 10.3 [3.2-33.8, respectively]). The population attributable risk was 31%. Fewer case mothers (46%) than control mothers (64%) reported being advised about sleep position in the hospital after delivery. Of those advised, a similar proportion of case mothers as control mothers were incorrectly told or recalled being told to use the prone position, but prone was recommended in a higher proportion of black mothers (cases and controls combined) compared with nonblack mothers.

CONCLUSIONS

Prone sleeping was found to be a significant risk factor for SIDS in this primarily African American urban sample, and approximately one third of the SIDS deaths could be attributed to this factor. Greater and more effective educational outreach must be extended to African American families and the health personnel serving them to reduce prone prevalence during sleep, which appears, in part, to contribute to the higher rates of SIDS among African American infants.

Physiologic studies on swaddling: an ancient child care practice, which may promote the supine position for infant sleep

OBJECTIVE

The calming effects of swaddling may help infants accept back sleeping and so reduce the risk of sudden infant death syndrome. We hypothesized that swaddling, with minimal leg restraint, would be accepted by postneonatal infants with minimal respiratory effects.

STUDY DESIGN

Postneonatal infants (n = 37)were studied for the introduction of swaddling. Four infants were studied by using traditional swaddling techniques. Swaddle tightness was increased in 13 infants, simulating traditional swaddles. Respiratory variables-respiratory rate, tidal volume, oxygen saturation, heart rate, sigh rate, and "grunting"-were measured.

RESULTS

Hips were flexed and abducted in the swaddle. The majority of infants accepted swaddling while supine, including 78% of infants who slept prone at home. Acceptance decreased with increasing age. With increased swaddle pressure, respiratory rate increased during quiet sleep (P <.05). In rapid eye movement sleep, a slight effect on heart rate was observed (P <.05). Other variables did not change.

CONCLUSIONS

Older infants including usual prone sleepers generally accept a form of swaddling that has minimal respiratory effects. The reintroduction of swaddling, without restricting hip movement or chest wall excursion, combined with supine sleeping, may promote further sudden infant death syndrome reduction.

Circumstances leading to a change to prone sleeping in sudden infant death syndrome victims

CONTEXT

In addition to usual prone sleeping, unaccustomed prone sleeping represents a significant risk factor for sudden infant death syndrome (SIDS). However, little information is available regarding the circumstances leading caretakers to change the infant's sleep position to prone position in SIDS victims.

OBJECTIVE

To determine, in a population of SIDS victims, the timing of a change to prone sleeping and the reason for that change in infants who were originally nonprone sleepers.

DESIGN AND SETTING

Case series analysis from a questionnaire administered between 1991 and 1997 to parents and other caretakers of SIDS victims in the province of Quebec (Canada).

SUBJECTS

One hundred fifty-seven SIDS cases occurring in the province during the study.

RESULTS

Of the 157 SIDS cases studied, 139 were found in the prone position, although only 93 infants usually slept prone. Of the 64 nonprone sleepers, 34 had been changed to prone by the parents or another caretaker before death, and 18 had apparently turned to prone for the first time. In the 34 cases changed to prone, the change occurred <1 week before death for 21 infants; for 16 of those infants, death occurred the first or second time that they slept prone. In 56% of the cases changed from a nonprone to prone sleeping position, a caretaker other than the parents had precipitated the change.

CONCLUSIONS

Ongoing campaigns to decrease the risk of SIDS should emphasize the risk of unaccustomed prone sleeping to both parents and secondary caretakers.

CLINICAL REVIEW ARTICLE: Is changing the sleep environment enough? Current recommendations for SIDS

Sudden infant death syndrome (SIDS or cot death) was the major cause of post-neonatal infant death in many countries in the late 1970s and 1980s. There is now very strong evidence that public intervention campaigns targeting the prone sleeping position, which had been identified by epidemiological studies as a major risk factor, were followed by substantial falls in the rate of SIDS. In the present review we discuss the evidence on which current recommendations for the prevention of SIDS are based. The prone sleeping position is now clearly causally associated with SIDS. Further reductions in SIDS may be produced by recommending the back sleeping position as opposed to the side position. Maternal smoking in pregnancy and bed sharing by infants of mothers who smoke are also strongly associated with SIDS, but have been harder to influence. Paternal smoking has also been implicated, although the magnitude of the reported risk is small. Finally, breastfeeding, pacifier use and having the infant sharing the parents bedroom, but not the bed, may also reduce risk. Continued reductions in SIDS mortality will require innovative public health education to target these major risk factors, while building on the "back to sleep" approach.

Gastric aspiration and sleeping position in infancy and early childhood

Concern has been expressed that the recommendation of supine sleeping position for infants would result in an increase in deaths due to gastric aspiration. A review of 196 cases of infant and early childhood death in children under 3 years of age, occurring over a 9-year period (September 1989 to August 1998) was undertaken to ascertain how many cases of significant gastric aspiration had occurred. Extensive and widespread filling of the airways/alveoli with gastric contents was found in three infants/young children aged 5, 6 and 30 months, respectively. In each instance the body had been found lying face down (prone), with the face in a pool of vomitus in at least one case. No cases of significant gastric aspiration were found in infants who had been found lying on their sides or backs (supine). In addition, no significant increase in numbers of infant and early childhood deaths in South Australia due to gastric aspiration over this time could be demonstrated. Concerns that the supine rather than the prone position is more likely to result in significant gastric aspiration are not supported by this study.

Birth weight- and gestational age-specific sudden infant death syndrome mortality: United States, 1991 versus 1995

OBJECTIVE

To estimate the changes in birth weight- and gestational age-specific sudden infant death syndrome (SIDS) mortality rates since the publication of the sleep-positioning recommendations by the American Academy of Pediatrics Task Force on Infant Positioning and SIDS.

METHODS

This is a historical cohort study using US vital statistic linked birth and infant death certificate files for the years 1991 and 1995. SIDS deaths were identified as any death attributed to International Classification of Diseases, Ninth Revision code 7980, occurring between the 28th and 365th days of life.

RESULTS

There were 4871 deaths attributed to SIDS in 1991 for a postneonatal mortality rate of 1.2/1000 postneonatal survivors compared with 3114 deaths in 1995 for a rate of.8/1000. This represents a 33% drop in the postneonatal SIDS mortality from 1991 to 1995. Between 1991 and 1995, SIDS rates declined 38%, 38%, 35%, and 32% for birth weight groupings of 500 to 999 g, 1000 to 1499 g, 1500 to 2499 g, and >/=2500 g, respectively. There were no SIDS deaths attributed to infants weighing <500 g. The SIDS rates declined 27%, 21%, 40%, and 23% for gestational age groups of <29 weeks, 29 to 32 weeks, 33 to 36 weeks, and >/=37 weeks. The rate of decline did not differ significantly across birth weight- or gestational age-specific categories. There was a significant increase in the black:non-black postneonatal SIDS mortality ratio from 2.00 to 2.28, reflecting a smaller decline in birth weight- and gestational age-specific mortality for blacks than observed for the non-black population.

CONCLUSION

Postneonatal SIDS mortality decreased significantly across all broad birth weight and gestational age categories. If the decline in the prevalence of prone positioning that has been reported since 1992 has occurred across all birth weight and gestational age, these data support the hypothesis that supine or side sleep positioning is effective in preterm/low birth weight infants as well as term infants.

Sudden infant death syndrome, virus infections and cytokines

Many epidemiological risk factors identified for sudden infant death syndrome (SIDS) suggest a viral aetiology, e.g. exposure to cigarette smoke and winter peak, mild respiratory symptoms. Virus infections and bacterial toxins induce cytokine activity and it has been suggested that uncontrolled inflammatory mediators could be involved in some cases of SIDS. The aim of this review was to assess the evidence for virus infection in SIDS and to examine those findings in relation to individual variations in cytokine responses and various pathophysiological mechanisms proposed for SIDS such as sleep derangement, hypoxia, cardiac arrhythmia, vascular hypotonicity and hypoglycaemia.

IL-6 cerebrospinal fluid levels are related to laryngeal IgA and epithelial HLA-DR response in sudden infant death syndrome

The objective was to investigate whether there is any correlation between signs of central and peripheral immune stimulation in victims of sudden infant death syndrome (SIDS), the former expressed by IL-6 in cerebrospinal fluid (CSF), the latter by IgA, IgG, and IgM immunocytes, T lymphocytes, and HLA-DR expression in laryngeal mucosa. Seventeen SIDS cases with low CSF IL-6 levels (< or =5 pg/mL) and 20 cases with high CSF IL-6 levels (> or =30 pg/mL) were subjected to immunohistochemical quantitation of IgA, IgG, and IgM immunocytes; semiquantitative scoring of T lymphocytes in the mucosa of epiglottis and larynx, and semiquantitative evaluation of HLA-DR expression. SIDS cases with IL-6 levels > or =30 pg/mL had a significantly higher number of IgA immunocytes in laryngeal mucosa (p = 0.007) and in epiglottis (p = 0.03) than cases with IL-6 levels < or =5 pg/mL. Furthermore, laryngeal HLA-DR expression was significantly more extensive in SIDS cases with IL-6 levels > or =30 pg/mL than in those with levels < or =5 pg/mL (p = 0.05). No differences were found for IgG and IgM immunocytes or for T cells. In addition, babies found prone more often had symptoms of slight infection before death and had a higher number of IgA immunocytes in the larynx (p = 0.02) than babies sleeping on their side or back. Because IL-6 levels > or =30 pg/mL correspond to the levels found in infants who die from infectious diseases such as meningitis/septicemia and pneumonia, the findings favor the hypothesis that many SIDS cases may be caused by an "overreaction" of the immune system to an otherwise harmless infection.

Living at high altitude and risk of sudden infant death syndrome

OBJECTIVE

To investigate the association between altitude of residence and risk of sudden infant death syndrome (SIDS).

METHODS

A retrospective, case control study in the Tyrol, Austria enrolled 99 infants with SIDS occurring between 1984 and 1994, and 136 randomly selected control cases. Data on pregnancy, delivery, child care practice, and socio-demographic characteristics including altitude of residence were collected with a standardised questionnaire.

RESULTS

The risk of SIDS increased gradually with increasing altitude of residence. This relation remained independently significant when the analysis was adjusted for gestational age, birth weight, prenatal care, mother's age at delivery, educational level of parents, and cigarette smoking during pregnancy. The prone sleeping position emerged as an obligatory cofactor in this association. In the whole of Austria, a similar trend of association emerged between the average altitudes in the 99 political counties and the rates of SIDS.

CONCLUSIONS

This study identified altitude of residence as a significant risk predictor of SIDS, primarily in combination with the prone sleeping position. Respiratory disturbances, reduced oxygen saturation, and lower temperatures at high altitude might explain this association.

SIDS--changes in the epidemiological pattern in eastern Norway 1984-1996

The objective was to analyse differences in the epidemiological pattern of sudden death in infancy during two time periods--the Sudden Infant Death Syndrome (SIDS) 'epidemic': 1984-1989, and the period of rapid decline in the SIDS rate 1990-1996. Sex distribution, age, sleeping position, signs of infection, day of the week and place of death were registered and compared for the two time periods studied in all SIDS cases autopsied at the Institute of Forensic Medicine, Oslo. There were significantly more deaths in the age group under four months in the period 1984-89 than in the second period. Prone sleeping position, signs of infection, death outdoors and during the winter were more frequent during the first period than in the second. These features also were more frequent in the age group under four months than in the older babies during the first period. The shift in the epidemiological pattern after 1990, when the risk factor campaign was launched, indicates that prone sleeping position, cold climate, sleeping outdoors and infections seem to be risk factors that are particularly harmful to the youngest infants.

Effects of temperature on sleep in the developing rat

In altricial species, such as humans and rats, much of the development of autonomic systems occurs postnatally. Consequently, vulnerabilities exist early in postnatal development when immature autonomic functions are challenged by external factors such as variations in ambient temperature (Ta). Ta profoundly influences sleep/wake state structure in adult animals and humans, and exposure to excessive warmth has been implicated as a risk factor in sudden infant death syndrome. To better understand the relationship between temperature and sleep during development, we investigated the effect of Ta variation on sleep/wake state structure and sleep intensity in developing rats. In this experiment, sleep intensity was measured by the intensity of slow-wave activity during slow-wave sleep. Neonatal Long-Evans hooded rat pups were surgically prepared for chronic sleep/wake state and brain temperature (Tbr) recording. Two-hour recordings of sleep/wake state and Tbr were obtained from rats on postnatal day 12 (P12), P14, P16, P18, and P20 at a Ta of either 28.0-30.0, 33.0-35.0, or 38.0-40.0 degrees C. Ta significantly influenced sleep/wake state structure but had little, if any, effect on sleep intensity in developing rats.

Problems on the diagnosis of sudden infant death syndrome

Various autopsy cases of sudden unexpected death (SUD) in infancy were examined at the Tokyo Medical Examiner's Office between 1985 and 1994. More than half of the SUD were diagnosed as sudden infant death syndrome (SIDS), but a number of other causes, such as mechanical asphyxia, were also diagnosed. SIDS is diagnosed by autopsy, but there are no clear diagnostic criteria differentiating SIDS from other causes of SUD. SUD is diagnosed as SIDS when other causes are excluded, but it is difficult to distinguish between SIDS and mechanical asphyxia. There was not a large difference in autopsy findings, or in death scene or statistical data, between SIDS and non-SIDS cases. In their estimation of the diagnostic ratio of SIDS to other causes of death, medical examiners might be divided into three groups: 'SIDS tolerationist' examiners think that SUD should be positively diagnosed as SIDS, insofar as another cause of death is not proved clearly. A second group of examiners might be regarded as 'SIDS exclusionist': these consider microscopic findings or peculiar death scenes as important contributing factors leading to death. The third group represents a middle stance somewhere between these two. We thought that (forensic) pathologists as well as medical examiners in Japan might have differing stances on SIDS diagnosis. The statistical analysis of SIDS in certain research areas may be affected by the diagnostic 'preference' of pathologists belonging to a certain institute.

Infant sleep position instruction and parental practice: comparison of a private pediatric office and an inner-city clinic

OBJECTIVE

To determine infant sleep instructions that hospital personnel in our community were giving to parents and actual positions practiced after the April 15, 1992 American Academy of Pediatrics recommendation for nonprone positioning.

DESIGN

Survey of mothers of infants </=4 months of age from November 1993 to March 1994 with follow-up survey of selected birth hospitals.

SETTING

A private practice (PP) serving predominantly white middle- and upper-income children and a pediatric clinic (CY) serving inner-city predominantly African-American low-income children in Louisville, Kentucky.

PATIENTS

Fifty infants from each practice site.

OUTCOME MEASURE

The sleep instructions given and practiced, and other risk factors for sudden infant death syndrome (SIDS).

RESULTS

Nonprone sleeping instructions were received by 72% of the PP and only 48% of the CY parents, with 72% of the PP and 54% of the CY following the nonprone recommendations. Infants were more likely to be in smoking households (60% vs 12%) from the CY practice than the PP practice.

CONCLUSIONS

Our study showed that, despite having a higher prevalence of SIDS risk factors, there was a greater delay in discontinuing prone positioning instructions in the hospital serving the CY infants. The evidence suggests that this population is as likely as the PP group to follow medical advice given.

Sleep architecture as related to temperature changes in neonates at term

Sleep architecture was assessed under different environmental temperatures in 10 full-term and 10 preterm infants who reached term. Five 30-min periods of baseline, normothermia heating, peak temperature, cooling and normothermia were analysed. A significant decrease in the proportion of active sleep (AS) and an increase in quiet sleep (QS) was noted among the full-term infants during the heating and peak temperature conditions, whereas, among the preterm infants, a similarly significant difference was noted during the heating and cooling stages of the study, but not during the stage of peak temperature. This differential response to environmental hyperthermia is possibly related to maturational factors. This phenomenon may be related to the increased vulnerability of low birth weight infants to apnoea and sudden infant death syndrome.

A potential danger of bedclothes covering the face

Investigations of infants dying unexpectedly have reported up to 28% being found completely under bedding. No detailed physiological studies looking at the possibilities of asphyxia in this situation are available. The aim was to determine the potential for asphyxia under different types and thicknesses of bedding. A mechanical model of a 3-month-old infant's respiratory system was used. Bedding was positioned over the head in a supine position, and inspired carbon dioxide recorded. With a fixed respiratory rate and tidal volume, carbon dioxide accumulation increased with increasing layers of blankets. Up to 8.3% inspired carbon dioxide was recorded with more than four layers of blankets. A cotton sheet between the face and blankets reduced the accumulation by half. An infant found dead under bedding may have been exposed to an asphyxial stress. Suffocation from rebreathing trapped, expired gases can be a cause of death in this situation.

Body temperature regulation in the newborn infant: interaction with sleep and clinical implications

Thermoregulation in newborn infant differs from that of adult. Comparisons between sleep stages show that, during rapid eye movements (REM) sleep, the impairment of thermoregulatory responses in adult is not observed in newborn. Both behavioral and autonomic temperature regulations are always operative in the range of air temperatures usually imposed. The interaction between sleep and thermoregulation seems to be less important in newborns than in adults, suggesting that sleep processes are well protected, reducing the probability of occurrence of central dysfunction. According to the model describing thermoregulation during sleep on the basis of changes in the hierarchical dominance of brain structures, either the influence of diencephalic structures is never depressed in REM sleep or the functional autonomy of the rhombencephalon is still relevant in the immature encephalon of the newborn. The thermoregulatory model also allows understanding of inter-individual differences in thermoregulation and levels of thermoneutrality. An attempt has also been made to learn the role of heat stroke in the production of sudden infant death syndrome when body heat loss is hampered.

Comparison of [125I]iodomelatonin binding sites in infant cerebellum of sudden infant death syndrome and non-sudden infant death syndrome

[125I]Iodomelatonin bindings sites in human infant cerebellum were studied by radioligand receptor binding assay and in vitro quantitative autoradiography. The binding sites characterized in membrane preparations revealed saturable, reversible and highly specific binding sites with a Kd value of 21.2 +/- 8.33 pM and a Bmax value of 2.02 +/- 0.52 fmol/mg protein. 10 microM of GTP gamma S significantly reduced the binding capacity, suggesting the possible G-protein coupling of the binding sites. Autoradiographic study showed that the labelling was mainly located in the cerebellar cortex. On comparison of the binding parameters from cerebellum of sudden infant death syndrome (SIDS) and non-SIDS infants, no significant change in binding capacity and binding affinity was detected. These findings suggest that the binding sites in cerebellum may not be related to the etiology of SIDS.

Accidental death or sudden infant death syndrome?

OBJECTIVE

To describe the reasons why it is difficult to decide whether to attribute some infant deaths to accidents or to SIDS.

METHODOLOGY

To extract from infant deaths data in South Australia those where the cause of death is debatable.

RESULTS

The risks associated with rocking cradles, bed sharing, bedclothes, couch sleeping, unsafe cots or beds and the prone position are presented.

CONCLUSIONS

Uniform worldwide death scene investigations for all infant deaths should help identify unsafe sleeping conditions for infants.

Sleeping position and sudden infant death syndrome in Norway 1967-91

OBJECTIVE

To investigate, in a population based national study, the association between sleeping position of infants and the occurrence of sudden infant death syndrome (SIDS).

DESIGN

A retrospective survey and registry based ecological study. A questionnaire based surveillance of sleeping position was obtained in a random sample (n = 34,799) and surveillance of SIDS was based on all infants born in Norway 1967-91, surviving the perinatal period. Variables studied from the questionnaire were usual sleeping position (placed), breast feeding at 3 months, and maternal smoking in pregnancy, and from the Medical Birth Registry maternal age, birth order, and birth weight.

RESULTS

Proportion of infants sleeping prone increased from 1970 (7.4%) to 1989 (49.1%) and dropped in 1990 (26.8%) and 1991 (28.3%). Occurrence of SIDS increased from 1970 (1.1/1000) to 1989 (2.0) before dropping in 1990 and 1991 (1.1). IMPLICATION AND RELEVANCE OF RESULTS: A cause effect relationship between prone sleeping and SIDS as suggested in previous studies is supported by the present; and so far only, national study of infants' sleeping position.

Sudden infant death syndrome prevention and an understanding of selected clinical issues

The etiology and prevention of sudden infant death syndrome (SIDS) are among the more frustrating topics in pediatrics. This article addresses several clinically relevant issues, including the relationships between apnea and SIDS, the nature of the "terminal event," effectiveness of home monitoring, the role of gastroesophageal reflux in apparent life-threatening events, and the association between the prone sleeping position and SIDS. This article is intended to provide the clinician with an awareness of the issues and the scientific basis needed to understand their contribution to SIDS.

The role of infectious agents in sudden infant death syndrome

Epidemiological factors associated with susceptibility to respiratory infections are similar to those associated with Sudden Infant Death Syndrome. Here we review the evidence that respiratory pathogens might be involved in some cases of Sudden Infant Death Syndrome in the context of factors identified in epidemiological studies of cot deaths: the age range affected; mother' smoking; respiratory viral infections; immunisation status. Both laboratory and epidemiological evidence suggests that vulnerability of infants to infectious agents depends on interactions between genetic, developmental and environmental factors that contribute to colonisation by microorganisms, the inflammatory and specific immune responses and the infants' physiological responses to inflammatory mediators. A model is proposed to explain how microorganisms might trigger a series of events resulting in some of these unexpected deaths and discusses how the the present recommendations regarding child care practices might help reduce the numbers of Sudden Infant Death Syndrome cases associated with infectious agents.

The micro-environment of the sleeping newborn piglet covered by bedclothes: gas exchange and temperature

This study followed the thermal and gaseous micro-environment of the newborn piglet sleeping under two levels of bedding insulation. After 1 h in the piglet's thermal comfort zone, the head of each piglet was covered for 2 h with bedding either 12 mm or 21 mm thick. Body temperature rose rapidly, but the arterial gases showed no change in the direction of asphyxia; with the thicker covering PaO2 was unchanged and PaCO2 fell and pH rose. These changes were despite a small rise in environmental PCO2 and fall in PO2 but were also minimized by the piglet's ability to avoid profound hypocapnia by panting at a very low tidal volume. No significant changes in blood gases occurred with the thinner bedding; the temperature rose markedly but more slowly. It is suggested that human babies submerged under bedclothes for any length of time would be more likely to succumb to the effects of hyperthermia than of asphyxia.

Factors potentiating the risk of sudden infant death syndrome associated with the prone position

BACKGROUND

In several studies the sudden infant death syndrome (SIDS) has been significantly associated with sleeping in the prone position. It is not known how the prone position increases the risk of SIDS.

METHODS

We analyzed data from a case-control study (58 infants with SIDS and 120 control infants) and a prospective cohort study (22 infants with SIDS and 213 control infants) in Tasmania. Interactions were examined in matched analyses with a multiplicative model of interaction.

RESULTS

In the case-control study, SIDS was significantly associated with sleeping in the prone position, as compared with other positions (unadjusted odds ratio, 4.5; 95 percent confidence interval, 2.1 to 9.6). The strength of this association was increased among infants who slept on natural-fiber mattresses (P = 0.05), infants who were swaddled (P = 0.09), infants who slept in heated rooms (P = 0.006), and infants who had had a recent illness (P = 0.02). These variables had no significant effect on infants who did not sleep in the prone position. A history of recent illness was significantly associated with SIDS among infants who slept prone (odds ratio, 5.7; 95 percent confidence interval, 1.8 to 19) but not among infants who slept in other positions (odds ratio, 0.83). In the cohort study, the risk of SIDS was greater among infants who slept prone on natural-fiber mattresses (odds ratio, 6.6; 95 percent confidence interval, 1.3 to 33) than among infants who slept prone on other types of mattresses (odds ratio, 1.8).

CONCLUSIONS

When infants sleep prone, the elevated risk of SIDS is increased by each of four factors: the use of natural-fiber mattresses, swaddling, recent illness, and the use of heating in bedrooms.

Effect of ambient temperature on SIDS rate

OBJECTIVE

To examine the relationship between ambient temperature and rate of sudden infant death syndrome (SIDS).

SUBJECTS AND SETTING

All infants with SIDS occurring during 1980-1989 in the Sydney metropolitan area.

RESULTS

The SIDS rate varied more than threefold over the months of the year and peaked at the minimum daily temperature in July. The rate was negatively linearly related to both the monthly mean minimum and maximum daily temperatures. Both relationships were highly significant (P < 0.001).

CONCLUSION

The significant relationship between daily temperature and SIDS rate means either that daily temperature is an excellent indicator of the cold weather conditions that have a profound effect on the rate of SIDS or that temperature itself plays a direct role in the cause of SIDS.

An analysis of trends in the incidence of sudden infant death in The Netherlands 1969-89

There is considerable interest in the relationship between sleeping position and the occurrence of sudden infant death syndrome (SIDS). As changes have been reported in The Netherlands in the position infants have been placed to sleep, the national Dutch sudden infant death rates were analyzed over the time that such changes have taken place. The overall post-perinatal death rate (1 week less than 1 year) was around 4-4.5 per 1000 live births from 1969 until 1985. From 1985 until 1989 the rate fell from 4.1 to 2.9 per 1000 live births. During the same period the cot death/SIDS rate rose from 0.44 per 1000 in 1969 to between 1.08 and 1.31 per 1000 in 1977-87, and subsequently fell to 0.7 per 1000 in 1989. These trends coincided with changes in prone sleeping position demonstrated in national surveys. The problems of interpreting such national data, with only 50-60% of infant deaths being autopsied and with the possibilities of misclassification over time, are fully discussed. The data are supportive of the relationship between prone sleeping position and cot death.

An overview of retrospective case-control studies investigating the relationship between prone sleeping position and SIDS

A critical overview of 19 case-control studies that have investigated the relationship between prone sleeping position and sudden infant death syndrome (SIDS) is presented. Issues relating to the non-comparability of the studies are described in terms of: (i) case definition; (ii) selection of controls; (iii) quality of the sleeping position data; (iv) recall bias; and (v) adjustment for confounding factors. All studies showed a positive association (2 out of the 19 studies were not significant) between prone sleeping position and SIDS. Meta-analysis techniques applied to six of these studies, based on 'usual' sleeping position in cases and population representative controls, has confirmed an overall higher risk of SIDS in infants who usually sleep prone. The most common odds ratio for an association between prone sleeping position and SIDS was 2.72 (95% confidence interval 2.27-3.26). The extent to which the methodological problems of retrospective case-control studies interfere with our interpretations of this association are discussed.