Sudden infant death syndrome

Geographic Variation in Sudden Unexpected Infant Death in the United States

OBJECTIVES

To assess the geographic variation of sudden unexpected infant death (SUID) and test if variation in geographic factors, such as state, latitude, and longitude, play a role in SUID risk across the US.

STUDY DESIGN

We analyzed the Centers for Disease Control and Prevention's Cohort Linked Birth/Infant Death dataset (2005-2010; 22 882 SUID cases, 25 305 837 live births, rate 0.90/1000). SUID was defined as infant deaths (ages 7-364 days) that included sudden infant death syndrome, ill-defined and unknown cause of mortality, and accidental suffocation and strangulation in bed. SUID geographic variation was analyzed using 2 statistical models, logistic regression and generalized additive model (GAM).

RESULTS

Both models produced similar results. Without adjustment, there was marked geographic variation in SUID rates, but the variation decreased after adjusting for covariates including known risk factors for SUID. After adjustment, nine states demonstrated significantly higher or lower SUID mortality than the national average. Geographic contribution to SUID risk in terms of latitude and longitude were also attenuated after adjustment for covariates.

CONCLUSION

Understanding why some states have lower SUID rates may enhance SUID prevention strategies.

A perspective on SIDS pathogenesis. the hypotheses: plausibility and evidence

Several theories of the underlying mechanisms of Sudden Infant Death Syndrome (SIDS) have been proposed. These theories have born relatively narrow beach-head research programs attracting generous research funding sustained for many years at expense to the public purse. This perspective endeavors to critically examine the evidence and bases of these theories and determine their plausibility; and questions whether or not a safe and reasoned hypothesis lies at their foundation. The Opinion sets specific criteria by asking the following questions: 1. Does the hypothesis take into account the key pathological findings in SIDS? 2. Is the hypothesis congruent with the key epidemiological risk factors? 3. Does it link 1 and 2? Falling short of any one of these answers, by inference, would imply insufficient grounds for a sustainable hypothesis. Some of the hypotheses overlap, for instance, notional respiratory failure may encompass apnea, prone sleep position, and asphyxia which may be seen to be linked to co-sleeping. For the purposes of this paper, each element will be assessed on the above criteria.

SIDS pathogenesis: pathological findings indicate infection and inflammatory responses are involved

This article explores the pathological evidence that supports the hypothesis that infection and inflammation are underlying mechanisms in SIDS. It reviews the pathological findings in relation to the risk factors reported for SIDS and compares these findings with other hypotheses suggested as causes of these unexplained deaths in infants. The roles of environmental factors and bacterial products such as soluble curlin detectable in SIDS sera in triggering cytokine cascades and aberrant inflammatory responses resulting in a toxic shock-like event are also explored. Areas for future research are outlined.

Sudden infant death syndrome: a critical review of approaches to research

This review explores the various research approaches taken attempting to solve the problem of SIDS. It would appear that major clues provided by pathological findings have been largely overlooked and as a consequence much effort, time, and money has been wasted on projects that satisfy only sub-specialty and political needs. Close examination of the pathological clues would provide better insights into the mechanisms underlying this enigmatic and heartbreaking problem.

SIDS: more facts and controversies

A more robust theory of the causation of sudden infant death syndrome (SIDS) is needed. The asphyxial theory of SIDS, which encompasses the prone sleeping position, relies on contradictory pathological evidence and fails to explain infants with SIDS who are found in the supine or lateral position. Many of the risk factors for SIDS point to an infective cause. The relative risks of these infection-related factors differ from study to study, as does the relative risk of prone sleeping position. I present the case for an infection model for SIDS causation, which has largely been neglected by mainstream SIDS researchers.

Ventilatory and arousal responses to respiratory stimuli of full term, intrauterine growth restricted lambs

We aimed to determine the effect of intrauterine growth restriction (IUGR) on the control of breathing and arousal in sleeping postnatal animals. We measured ventilatory and arousal responses to respiratory challenges during sleep in normally grown (birthweight 5.17+/-0.48 kg) and IUGR (2.64+/-0.19 kg) full term lambs. During wakefulness, IUGR lambs had significantly lower arterial pH and higher Pa(CO(2)) levels. During quiet sleep, but not active sleep, end tidal CO(2) was elevated in IUGR lambs (P=0.08). During active and quiet sleep, minute ventilation (per kg body weight) was significantly higher in IUGR lambs than controls. Ventilatory responses to hypercapnia and/or hypoxia were not different between control and IUGR lambs during active and quiet sleep but end tidal CO(2) at arousal was consistently higher in IUGR lambs; other indices of arousal were not affected by IUGR. Our findings suggest IUGR lambs require an elevated level of ventilation to maintain respiratory homeostasis and that alterations in lung function are likely consequences of IUGR.

Ventilatory and arousal responses of sleeping lambs to respiratory challenges: effect of prenatal maternal anemia

We have examined the effects of exposure to chronic maternal anemia, throughout the final one-third of gestation, on postnatal ventilatory and arousal responses to hypoxia, hypercapnia, and combined hypoxia-hypercapnia in sleeping lambs. While resting quietly awake, lambs from anemic ewes had higher arterial PCO(2) levels than control animals during the first 2-3 postnatal wk, but pH, arterial PO(2), and arterial O(2) saturation were not different. During active and quiet sleep lambs from anemic ewes had higher end-tidal CO(2) levels than control animals when breathing room air and at the time of spontaneous arousal or when aroused by progressive hypercapnia or by combined hypoxia-hypercapnia. Ventilation and arterial O(2) saturation during uninterrupted sleep and ventilatory responsiveness to hypoxia (inspiratory O(2) fraction, 10%), progressive hypercapnia, and combined hypoxia/hypercapnia were not significantly affected by exposure to maternal anemia. Our findings show that maternal anemia results in elevated PCO(2) levels in the offspring. This effect may be due, at least in part, to altered pulmonary function.

Lethal synergy between toxins of staphylococci and enterobacteria: implications for sudden infant death syndrome

AIM

To test the hypothesis that lethal synergy occurs between toxin preparations of nasopharyngeal staphylococci and enterobacteria from sudden infant death syndrome (SIDS) victims and matched healthy infants.

METHODS

SIDS and matched healthy babies were studied if both staphylococcal and enterobacterial strains were isolated from the nasopharynx. The lethality of toxin preparations from each bacterial isolate (separately and combined) was assessed over a range of dilutions using the chick embryo assay system.

RESULTS

Staphylococci and enterobacteria were isolated together from the nasopharynx of seven SIDS babies but from only one normal healthy infant. Enterobacterial toxins were lethal at high dilutions. Staphylococcal toxins were less toxic. Simultaneous testing in the chick assay of staphylococcal and enterobacterial toxins, from each baby, at non-lethal concentrations enhanced lethality levels by 177 to 1011% compared with lethality expected by an additive effect alone.

CONCLUSIONS

Synergy occurs between the toxins of nasopharyngeal staphylococci and enterobacteria. This combination of strains is more likely to occur in the nasopharynx of SIDS victims than that of healthy infants.

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.

Epidemiology of sudden infant death syndrome in Japan

An epidemiological survey was carried out to examine the present situation with respect to sudden infant death syndrome (SIDS) in Kanagawa Prefecture. Questionnaires on sudden unexpected death of infants aged < 1 year in 1990-91 were sent to the hospitals and clinics in Kanagawa Prefecture which may take care of such infants. By analysing information from 10,485 replies, 48 out of 73 reported sudden infant deaths were confirmed to be SIDS, although autopsy was not performed in 13 cases (27%). The incidence of SIDS per 1000 live births in Kanagawa Prefecture was 0.29 in 1990 and 0.31 in 1991; and if limited to autopsy cases 0.19 and 0.25, respectively. Sudden infant death syndrome cases in Japan were found to occur more frequently when infants were < 6 months old, at home and sleeping alone, but less in the winter and between midnight and early morning. There was little difference between the numbers in prone and supine sleeping positions at discovery. It was not clear whether SIDS occurred more often to babies sleeping prone than supine, because there were no controls matched with the SIDS cases. In future, continuous epidemiological surveys of SIDS in Japan should be carried out.

Climatic temperature and variation in the incidence of sudden infant death syndrome between the Australian states

OBJECTIVE

To describe the relationship between climatic temperature and the incidence of sudden infant death syndrome (SIDS) for the Australian States and examine the extent to which differences in climatic temperature might explain the regional variation of SIDS in Australia.

DESIGN

Case series study. A generalised linear model was used to model the association between monthly average temperature and the incidence of SIDS.

SETTING

The report is population based. Data are available from all Australian States.

SUBJECTS

Cases of SIDS from birth to less than 12 months of age occurring in Queensland (1981-1987), New South Wales (1981-1987), Victoria (1984-1987), Tasmania (1975-1989), South Australia (1980-1989), and Western Australia (1980-1988).

RESULTS

Every one degree Celsius decrease in average monthly temperature within the range 9 degrees C to 25 degrees C is associated with a 10.6% (95% confidence interval, 9.6%-11.7%) increase in the incidence of SIDS. Climatic temperature accounts for 84% of the interstate variation in the rate of SIDS. After controlling for the effect of temperature, a significant overall difference in SIDS incidence remains (P less than 0.0001) for the Australian States.

CONCLUSION

Climatic temperature accounts for most but not all of the regional variation of SIDS incidence in the Australian States. The remaining variation may reflect differences in the maternal and infant characteristics of the State populations.