Viruses and sudden infant death

Sudden Infant Death Syndrome: Risk Factors and Newer Risk Reduction Strategies

Sudden infant death syndrome (SIDS) continues to be one of the top causes of infant death in the U.S. Despite significant public health initiatives focused on high-risk populations to enhance sleep environments and techniques. The SIDS rate has remained stable in recent years. Risk factors and newer risk reduction strategies for SIDS are the focus of this review article. We conducted a comprehensive literature search on Medline, Cochrane, Embase, and Google Scholar until July 2022. The following search strings and Medical Subject Heading (MeSH) terms were used: "SIDS," "Sudden Infant Death" and "SUID". We explored the literature on SIDS for its epidemiology, pathophysiology, the role of various etiologies and their influence, associated complications leading to SIDS, and preventive and treatment modalities. Despite a more than 50% drop-in rates since the start of the "Back to Sleep" campaign in 1994, sudden infant death syndrome (SIDS) continues to be the top cause of post-neonatal mortality in the United States, despite continued educational initiatives that support safe sleep and other risk reduction strategies. The new American Academy of Pediatrics guidelines for lowering the risk of SIDS include a lot of emphasis on sleeping habits, bedding, and environment but also include elements that are frequently ignored (i.e., prenatal care, smoking, alcohol and drug use, and childhood vaccinations). This study highlights these less-frequently discussed aspects and identifies treatments that have produced beneficial behavioral shifts that benefit newborns as well as their mothers' health and wellbeing.

Pulmonary immune profiling of SIDS: impaired immune maturation and age-related cytokine imbalance

BACKGROUND

For sudden infant death syndrome (SIDS), an impaired immunocompetence has been discussed for a long time. Cytokines and chemokines are soluble immune mediators (SIM) whose balance is essential for the immune status. We hypothesized that an imbalanced immune response might contribute to the etiology of SIDS.

METHODS

We investigated 27 cytokines, chemokines, and growth factors in protein lysates of lungs derived from 29 SIDS cases and 15 control children deceased for other reasons.

RESULTS

Except for the CCL5, no significant differences were detected in the lungs between SIDS cases with and without mild upper respiratory tract infections. In contrast, IL-1RA, IL-7, IL-13, and G-CSF were decreased in the merged SIDS cases compared to control cases without evidence of infection. Plotting SIM concentrations against infant age resulted in increasing concentrations in control but not in SIDS lungs, indicating a disturbed immune maturation. Moreover, an age-dependent shift towards a Th2-related pattern was observed in SIDS.

CONCLUSIONS

Our findings suggest that an impaired maturation of the immune system, an insufficient response to respiratory pathogens, and an immune response modulated by Th1/Th2 imbalance might play a possible role in triggering SIDS. These findings might in part be explained by chronic stress.

IMPACT

Maturation of the cytokine and chemokine network may be impaired in SIDS. An imbalance between Th1- and Th2-related cytokines, which may reflect a state of chronic stress causing a more Th2 shift. An impaired immune maturation, an insufficient response to respiratory pathogens, and an immune response modulated by Th1/Th2 imbalance might play a possible role in SIDS.

Peripheral Neuroplasticity of Respiratory Chemoreflexes, Induced by Prenatal Nicotinic Exposure: Implication for SIDS

Sudden Infant Death Syndrome (SIDS) occurs during sleep in seemingly healthy infants. Maternal cigarette smoking and hypoxemia during sleep are assumed to be the major causal factors. Depressed hypoxic ventilatory response (dHVR) is observed in infants with high risk of SIDS, and apneas (lethal ventilatory arrest) appear during the fatal episode of SIDS. Disturbance of the respiratory center has been proposed to be involved, but the pathogenesis of SIDS is still not fully understood. Peripherally, the carotid body is critical to generate HVR, and bronchopulmonary and superior laryngeal C-fibers (PCFs and SLCFs) are important for triggering central apneas; however, their roles in the pathogenesis of SIDS have not been explored until recently. There are three lines of recently accumulated evidence to show the disorders of peripheral sensory afferent-mediated respiratory chemoreflexes in rat pups with prenatal nicotinic exposure (a SIDS model) in which acute severe hypoxia leads to dHVR followed by lethal apneas. (1) The carotid body-mediated HVR is suppressed with a reduction of the number and sensitivity of glomus cells. (2) PCF-mediated apneic response is largely prolonged via increased PCF density, pulmonary IL-1β and serotonin (5-hydroxytryptamine, 5-HT) release, along with the enhanced expression of TRPV1, NK₁R, IL1RI and 5-HT₃R in pulmonary C-neurons to strengthen these neural responses to capsaicin, a selective stimulant to C-fibers. (3) SLCF-mediated apnea and capsaicin-induced currents in superior laryngeal C-neurons are augmented by upregulation of TRPV1 expression in these neurons. These results, along with hypoxic sensitization/stimulation of PCFs, gain insight into the mechanisms of prenatal nicotinic exposure-induced peripheral neuroplasticity responsible for dHVR and long-lasting apnea during hypoxia in rat pups. Therefore, in addition to the disturbance in the respiratory center, the disorders of peripheral sensory afferent-mediated chemoreflexes may also be involved in respiratory failure and death denoted in SIDS victims.

Clinical and experimental aspects of breathing modulation by inflammation

Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.

Coxsackievirus B heart infections and their putative contribution to sudden unexpected death: An 8-year review of patients and victims in the coastal region of Tunisia

Coxsackieviruses B (CV B) are known as the most common viral cause of human heart infections. Cardiac inflammations contribute to sudden unexpected death (SUD) significantly. The diagnosis remains difficult with the traditional diagnostic tests and must be substantially improved. This has prompted health professionals to seek new diagnostic procedures which may provide important clues regarding underlying etiology. The present study is based on patients with infectious heart diseases and SUD victims with no relevant pathologies. They were investigated for possible CV-B infection. Patients with coronary artery diseases and unnatural road and domestic accident victims served as controls. The samples were studied for CV-B applying PCR. Histopathology for inflammatory markers, immunohistochemistry (IHC) for immune inflammatory cells and the enteroviral VP1-capsid protein were performed. Overall, 102 patients and 87 SUD victims were studied. As controls, 100 patients and 54 SUD unnatural accident victims were enrolled. CV-B were detected in 28 patients and 15 SUD victims. The control group samples were completely virus negative. Compared to controls, IHC revealed a significant presence of T and B lymphocytes within the myocardium. Furthermore, enteroviral VP1-capsid protein were detected from samples by IHC. Applying a comprehensive combination of methods, our results demonstrate the involvement of CV-B in cases of heart infection suggesting they play a significant role in SUD. Our results emphasize the importance of opting for a combination of methods.

Seasonal Timing of Infant Bronchiolitis, Apnea and Sudden Unexplained Infant Death

Rates of Sudden Unexplained Infant Death (SUID), bronchiolitis, and central apnea increase in winter in temperate climates. Though associations between these three conditions are suggested, more work is required to establish if there is a causal pathway linking bronchiolitis to SUID through inducing central apnea. Utilizing a large population-based cohort of infants studied over a 20-year period (n = 834,595, from birth years 1989–2009)), we analyzed ecological associations between timing of SUID cases, bronchiolitis, and apnea healthcare visits. Data were analyzed between 2013 and 2015. We used a Cox Proportional Hazards model to analyze possible interactions between maternal smoking and maternal asthma with infant bronchiolitis on time to SUID. SUID and bronchiolitis both occurred more frequently in winter. An increase in bronchiolitis clinical visits occurred within a few days prior to apnea visits. We found a temporal relationship between infant bronchiolitis and apnea. In contrast, no peak in SUID cases was seen during peaks of bronchiolitis. Among those without any bronchiolitis visits, maternal smoking was associated with an increased risk of SUID: Hazard Ratio (HR) of 2.38 (95% CI: 2.11, 2.67, p-value <0.001). Maternal asthma was associated with an increased risk of SUID among infants with at least one bronchiolitis visit: HR of 2.40 (95% CI: 1.04, 5.54, p-value = 0.04). Consistent trends between bronchiolitis, apnea, and SUID were not established due to small numbers of SUID cases. However, interaction analysis revealed potential differential associations of bronchiolitis and SUID by maternal smoking, maternal asthma status.

Postmortem diagnosis of infectious heart diseases: A mystifying cause of Sudden Infant Death

Sudden infant death (SID) is an unresolved problem of high relevance and previous studies have indicated a role of viral heart infections. The diagnosis remains difficult in clinical practice using routine diagnostic tests and must be substantially improved. A prospective study based on post-mortem samples from SID victims whose heart disease was not clinically recognized was conducted for 4 years in a Tunisian University Hospital. Pediatric cases of unnatural death served as controls. Both SID victims and controls were investigated for possible coxsackievirus-B (CV-B) infection in heart tissue. During the study period, 39 cases with a male predominance (77%) were reported. There was no positive family history of coronary artery disease among the victims. In 35 cases (90%), low birth weight and/or critical development period were reported. All SID victims had complained of mild fever and insomnia for a few days preceding death, which required infectious laboratory investigations marked with an elevated white blood cell count (WBC) and C-reactive protein (CRP). The cardiac biomarkers were also elevated. The histopathological investigations of the heart tissue samples revealed signs of myocardial and pericardial inflammation. Enterovirus was detected by immunohistochemistry (IHC) and PCR from myocardial samples from 6 cases (15.3%) having myocarditis and 3 cases (7.7%) having perimyocarditis. The current study is of great interest and is aimed at urging health professionals to adopt systematically long intensive heart care in infants with underlying vulnerability as well as new diagnostic approaches including histopathology complemented with IHC and molecular pathology.

Infectious causes of sudden infant death syndrome

Investigators have long suspected the role of infection in sudden infant death syndrome (SIDS). Evidence of infectious associations with SIDS is accentuated through the presence of markers of infection and inflammation on autopsy of SIDS infants and isolates of some bacteria and viruses. Several observational studies have looked into the relation between seasonality and incidence of SIDS, which often showed a winter peak. These all may suggest an infectious aetiology of SIDS. In this review we have summarised the current literature on infectious aetiologies of SIDS by looking at viral, bacterial, genetic and environmental factors which are believed to be associated with SIDS.

Frequency of apnea and respiratory viruses in infants with bronchiolitis

The frequency of apnea in infants <12 months of age admitted with acute bronchiolitis was 5.16% (95% confidence interval: 3.94-6.72). Most commonly detected viruses in the 51 apneic infants were respiratory syncytial virus (33.3%), rhinovirus (13.7%) and viral coinfections (23.5%). Young age and prematurity were the main risk factors for apnea independent of the respiratory syncytial virus status. Non-respiratory syncytial virus infants had a higher rate of prematurity.

Response of smooth bronchial musculature in bronchoconstrictor substances in newborn with lung atelectasis at the respiratory distress syndrome (RDS)

Objective:

Role of the atelectasis (hypoxia) in the respiratory system of the live and exited newborn (250 up to 3000 g. of body weight), which has died due to different causes was studied in this work.

Methods:

Response of tracheal rings to dopamine, serotonine and ethanol in the different molar concentrations (dopamine: 0,05 mg/ml, 0,5 mg/ml, 5 mg/ml; serotonine (5-HT): 10^-4, 10^-3, 10^-2, 10^-1 mol/dm³; ethanol: 0,2 ml, 0,5 ml, 1,0 ml; 96%) was followed up. Study of the smooth tracheal musculature tone (STM) was elaborated in 16 tracheal preparations taken following the newborn death due to different causes.

Results:

Based on functional researches of tracheal isolated preparations, it was ascertained as follows: atelectasis (cases born with lung hypoxia) has changed the response of STM to dopamine, serotonine and ethanol in a significant manner (p<0,01) in comparison to cases of controlling group, which has died due to lung inflammatory processes (e.g. pneumonia, bronchopneumonia, cerebral hemorrhage), which have also caused significant response (p<0,05).

Conclusion:

Results suggest that exited cases from lung atelectasis and cases of controlling group reacts to above mentioned substances by causing significant constrictor action of tracheobronchial system.

Post-mortem diagnosis, of cytomegalovirus and varicella zoster virus co-infection by combined histology and tissue molecular biology, in a sudden unexplained infant death

BACKGROUND

An autopsy case of a two-month-old male infant who suddenly and unexpectedly died during his sleep, eight days after the onset of benign varicella.

OBJECTIVES

To describe post-mortem combined histological and tissue molecular biological techniques for the diagnosis of cytomegalovirus and varicella zoster virus co-infection as a cause of death.

STUDY DESIGN

Real-time quantitative PCR and RT-PCR assays for Herpesviruses, respiratory viruses, Adenovirus, Enterovirus and Parvovirus B19 were performed on multi-organ frozen samples and paraffin-embedded tissues in combination with histology.

RESULTS

Cytomegalovirus and varicella zoster virus were detected by molecular biology with highest viral loads detected in the lungs (4.6×10(7) and 1.9×10(5) genome copies per million of cells, respectively). Pulmonary extensive necrotizing inflammation and immunohistochemistry correlated to virological data. Virological molecular biology was negative on paraffin-embedded tissues.

CONCLUSIONS

This case shows that thorough quantitative virological investigations on frozen tissues must be performed in combination with histology and immunohistochemistry for the determination of the cause of a sudden unexplained infant death.

Configurative domains in child health research: sudden infant death in the Swedish Medical Journal

The aim of present investigation is to discover publishing portrayals embedded in sudden infant death informatics disseminated by a medical journal at regional level. In particular, gender configurative domains regarding health policy and nursing practices are scrutinized. A qualitative literature review was performed using a critical discourse analytical approach. The full texts of 55 articles/comments published within the field by the Swedish Medical Journal from January 1, 1980 to March 6, 2007 were examined. Four configurative domains were recognized as setting the agenda and as working throughout the reviewed text viz., (a) the clinical-medical episteme, (b) the individualized family domain, (c) gender domains in prevention and nursing practices, and finally (d) the configurative entry into gendered academic writing of the subject in view. The skewed gendered publishing portrayals observed were consistent throughout more than two decades. Gender analysis in child health research is highlighted.

Inflammatory responses to acute pneumovirus infection in neonatal mice

Background

The innate immune responses of neonates differ dramatically from those of adults. Here we examine the acute inflammatory responses of neonatal and weanling mice infected with pneumonia virus of mice (PVM), a rodent pathogen (family Paramyxoviridae, genus Pneumovirus) that replicates the sequelae of severe respiratory syncytial virus infection.

Results

We demonstrate that virus replication proceeds indistinguishably in all age groups (inoculated at 1, 2, 3 and 4 weeks of age), although inflammatory responses vary in extent and character. Some of the biochemical mediators detected varied minimally with age at inoculation. Most of the mediators evaluated demonstrated elevated expression over baseline correlating directly with age at the time of virus inoculation. Among the latter group are CCL2, CCL3, and IFN-γ, all cytokines previously associated with PVM-induced inflammatory pathology in mature mice. Likewise, we detect neutrophil recruitment to lung tissue in all age groups, but recruitment is most pronounced among the older (3 - 4 week old) mice. Interestingly, all mice exhibit failure to thrive, lagging in expected weight gain for given age, including the youngest mice that present little overt evidence of inflammation.

Conclusions

Our findings among the youngest mice may explain in part the phenomenon of atypical or minimally symptomatic respiratory infections in human neonates, which may be explored further with this infection model.

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.

Acute life threatening event (ALTE) in an infant with human coronavirus HCoV-229E infection

In this short report we discuss the temporal association between an acute life threatening event (ALTE) and a RT-PCR confirmed coronavirus HCoV-229E infection in a 4 months old otherwise healthy infant. More detailed microbiological investigations of affected children even without apparent signs of a respiratory tract infection may help to clarify the etiology in some patients and extend our understanding of the pathogenesis. PCR-based techniques should be utilized to increase the sensitivity of detection for old and new respiratory viral pathogens in comparable cases.

Respiratory syncytial virus infection in anesthetized weanling rather than adult rats prolongs the apneic responses to right atrial injection of capsaicin

Apnea is a common complication in infants infected by respiratory syncytial virus (RSV). A recent study has shown that intranasal inoculation of RSV in conscious weanling rats strengthens the apneic responses to right atrial injection of capsaicin (CAP), leading to 66% mortality. The objectives of the present study were to determine 1) whether RSV infection changes baseline minute ventilation (Ve) and arterial blood gases in anesthetized rats; 2) what the effects of RSV infection are on the respiratory responses to CAP; and 3) whether the RSV-strengthened apneic responses are age dependent. Our experiments were conducted in anesthetized and spontaneously breathing rats divided into four groups of weanling and adult rats that received either intranasal inoculation of RSV or virus-free medium. Two days after RSV infection (0.7 ml/kg), animal blood gases, baseline Ve, and Ve responses to right atrial injection of three doses of CAP (4, 16, and 64 microg/kg) were measured and compared among the four groups. Our results showed that RSV infection increased respiratory frequency (approximately 25%, P<0.05) in weanling but not adult rats, with little effect on arterial blood gases. RSV infection amplified the apneic responses to CAP in weanling but not adult rats, characterized by increases in the initial (40%) and the longest apneic duration (650%), the number of apneic episodes (139%), and the total duration of apneas (60%). These amplifications led to 50% mortality (P<0.05). We conclude that RSV infection increases respiratory frequency and strengthens the apneic responses to CAP only in anesthetized weanling but not adult rats.

Virological analysis in the diagnosis of sudden children death: A medico-legal approach

Infections are considered to be an important cause of unexpected death in children. It has also been assumed that respiratory viruses are involved in the genesis of sudden infant death syndrome (SIDS). The Spanish National Institute of Toxicology and Forensic Sciences act as the forensic reference centre for Spain. We analyse the experience of this centre in the virological study of 64 cases of sudden children death where viral serology, virological cultures, herpesviruses polymerase chain reaction (PCR) and electron microscopy were performed. According to pathological findings, death could only be attributed to an adenovirus infection in one amygdalitis with upper airways stenosis and asphyxia. Human herpes virus 6 (HHV-6) was detected by PCR in one case with pathological findings characteristic of SIDS. Recent infection by respiratory syncytial virus (RSV), Epstein-Barr virus (EBV) and cytomegalovirus (CMV) were also detected. Meanwhile, 85.9% of the cases yielded negative viral results. Twenty-eight infants were finally categorised as SIDS. Pathological findings of infection were detected in 12 patients despite the negativity of viral analyses. Although viral infection is an uncommon cause of sudden children death, a complete microbiological investigation will help to solve the puzzle of SIDS. Definitive guidelines for microbiological analyses need to be updated whilst new pathogens are discovered or new techniques are implemented in order to clarify unsolved cases.

Effect of respiratory syncytial virus on apnea in weanling rats

Apnea is a common complication of respiratory syncytial virus (RSV) infection in young infants. The purpose of this study was to determine whether this infection affects apnea triggered by sensorineural stimulation in weanling rats. We also studied which neurotransmitters are involved in this response and whether passive prophylaxis with a specific neutralizing antibody (palivizumab) confers protection against it. Weanling rats were inoculated intranasally with RSV, adenovirus, or virus-free medium. Changes in respiratory rate and apnea in response to nerve stimulation with increasing doses of capsaicin were measured by plethysmography. Capsaicin-induced apnea was significantly longer in RSV-infected rats at postinoculation days 2 (upper airways infection) and 5 (lower airways infection), and apnea-related mortality occurred only in the RSV-infected group. Reduction in the duration of apnea was observed after selective inhibition of central gamma-aminobutyric acid (GABA) type A receptors and neurokinin type 1 receptors for substance P. Prophylactic palivizumab protected against apnea and apnea-related mortality. These results suggest that sensorineural stimulation during RSV infection is associated with the development of apnea and apnea-related death in early life, whose mechanism involves the release of GABA acting on central GABA type A receptors and substance P acting on neurokinin type 1 receptors.

Possible pathomechanisms of sudden infant death syndrome: key role of chronic hypoxia, infection/inflammation states, cytokine irregularities, and metabolic trauma in genetically predisposed infants

Chronic hypoxia, viral infections/bacterial toxins, inflammation states, biochemical disorders, and genetic abnormalities are the most likely trigger of sudden infant death syndrome (SIDS). Autopsy studies have shown increased pulmonary density of macrophages and markedly more eosinophils in the lungs accompanied by increased T and B lymphocytes. The elevated levels of immunoglobulins, about 20% more muscle in the pulmonary arteries, increased airway smooth muscle cells, and increased fetal hemoglobin and erythropoietin are evidence of chronic hypoxia before death. Other abnormal findings included mucosal immune stimulation of the tracheal wall, duodenal mucosa, and palatine tonsils, and circulating interferon. Low normal or higher blood levels of cortisol often with petechiae on intrathoracic organs, depleted maternal IgG antibodies to endotoxin core (EndoCAb) and early IgM EndoCAb triggered, partial deletions of the C4 gene, and frequent IL-10-592*A polymorphism in SIDS victims as well as possible hypoxia-induced decreased production of antiinflammatory, antiimmune, and antifibrotic cytokine IL-10, may be responsible for the excessive reactions to otherwise harmless infections. In SIDS infants, during chronic hypoxia and times of infection/inflammation, several proinflammatory cytokines are released in large quantities, sometimes also representing a potential source of tissue damage if their production is not sufficiently well controlled, eg, by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). These proinflammatory cytokines down-regulate gene expression of major cytochrome P-450 and/or other enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity, thus affecting metabolism of several endogenous lipophilic substances, such as steroids, lipid-soluble vitamins, prostaglandins, leukotrienes, thromboxanes, and exogenous substances. In SIDS victims, chronic hypoxia, TNF-alpha and other inflammatory cytokines, and arachidonic acid (AA) as well as n-3 polyunsaturated fatty acids (FA), stimulated and/or augmented superoxide generation by polymorphonuclear leukocytes, which contributed to tissue damage. Chronic hypoxia, increased amounts of nonheme iron in the liver and adrenals of these infants, enhanced activity of CYP2C9 regarded as the functional source of reactive oxygen species (ROS) in some endothelial cells, and nicotine accumulation in tissues also intensified production of ROS. These increased quantities of proinflammatory cytokines, ROS, AA, and nitric oxide (NO) also resulted in suppression of many CYP450 and other enzymes, eg, phosphoenolpyruvate carboxykinase (PEPCK), an enzyme important in the metabolism of FA during gluconeogenesis and glyceroneogenesis. PEPCK deficit found in SIDS infants (caused also by vitamin A deficiency) and eventually enhanced by PACAP lipolysis of adipocyte triglycerides resulted in an increased FA level in blood because of their impaired reesterification to triacylglycerol in adipocytes. In turn, the overproduction and release of FA into the blood of SIDS victims could lead to the metabolic syndrome and an early phase of type 2 diabetes. This is probably the reason for the secondary overexpression of the hepatic CYP2C8/9 content and activity reported in SIDS infants, which intensified AA metabolism. Pulmonary edema and petechial hemorrhages often present in SIDS victims may be the result of the vascular leak syndrome caused by IL-2 and IFN-alpha. Chronic hypoxia with the release of proinflammatory mediators IL-1alpha, IL-1beta and IL-6, and overloading of the cardiovascular and respiratory systems due to the narrowing airways and small pulmonary arteries of these children could also contribute to the development of these abnormalities. Moreover, chronic hypoxia of SIDS infants induced also production of hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulated synthesis and release of different growth factors by vascular endothelial cells and intensified subclinical inflammatory reactions in the central nervous system, perhaps potentiated also by PACAP and VIP gene mutations. These processes could lead to the development of brainstem gliosis and disorders in the release of neuromediators important for physiologic sleep regulation. All these changes as well as eventual PACAP abnormalities could result in disturbed homeostatic control of the cardiovascular and respiratory responses of SIDS victims, which, combined with the nicotine effects and metabolic trauma, finally lead to death in these often genetically predisposed children.

Seasonal variation of sudden infant death syndrome in Hawaii

OBJECTIVE

To test whether the sudden infant death syndrome (SIDS) rate displays the universal winter maximum and summer minimum in Hawaii where there is no appreciable seasonal variation of temperature.

DESIGN

The null hypothesis is tested that there is no seasonal variation of necropsied SIDS in Hawaii. The numbers of live births and SIDS cases by month for the years 1979 to 2002 were collected and the monthly SIDS distribution is predicted based on the age at death distribution.

SETTING

The state of Hawaii, located in the midst of the Pacific Ocean, has a semi-tropical climate with temperatures fluctuating diurnally as 25 +/- 5 degrees C throughout the year. Therefore homes are unheated and infants are not excessively swaddled. The Hawaii State Department of Health maintains vital statistics of all infant births and deaths.

MAIN RESULTS

The results reject the null hypothesis of no seasonal variation of SIDS (p = 0.026). An explanation for the seasonal effect of the winter maximum and summer minimum for Hawaiian SIDS is that it arises from the cycle of the school session and summer vacation periods that represent variable intensity of a possible viral infection vector. SIDS rates in both Hawaii and the United States increase with parity, also indicating a possible role of school age siblings as carriers.

CONCLUSIONS

The winter peak of the SIDS in Hawaii is support for the hypothesis that a low grade viral infection, insufficient by itself to be a visible cause of death at necropsy, may be implicated as contributing to SIDS in vulnerable infants.

Sudden infant death syndrome, infection and inflammatory responses

Sudden infant death syndrome (SIDS) is sudden unexpected death in infancy for which there is no explanation after review of the history, a death scene investigation and a thorough autopsy. The use of common diagnostic criteria is a prerequisite for discussing the importance of infection, inflammatory responses and trigger mechanism in SIDS. Several observations of immune stimulation in the periphery and of interleukin-6 elevation in the cerebrospinal fluid of SIDS victims explain how infections can play a role in precipitating these deaths. Finally, these findings and important risk factors for SIDS are integrated in the concept of a vicious circle for understanding the death mechanism. The vicious circle is a concept to elucidate the interactions between unfavourable factors, including deficient auto-resuscitation, and how this could result in death.

Mucosal immune responses to infections in infants with acute life threatening events classified as 'near-miss' sudden infant death syndrome

This study examined the hypothesis that dysregulation of mucosal immune responses to respiratory infections is a critical event, which could be causal in respiratory arrest of some previously healthy infants. To examine this hypothesis, a prospective study was undertaken of infants presenting to the emergency department of a major teaching hospital with acute life threatening events (ALTE) of unknown cause and classified as "near-miss" SIDS. Salivary immunoglobulin concentrations were measured on admission and again after 14 days. The salivary immunoglobulins were compared with three control groups: infants with a mild upper respiratory tract infection (URTI); bronchiolitis; and healthy age-matched infants. The salivary IgA and IgM concentrations in the ALTE infants at presentation to hospital indicated a significant mucosal immune response had already occurred, with nearly 60% of the IgA concentrations significantly above the population-based reference ranges. The hyper-immune response was most evident in the ALTE infants with pathology evidence of an infection; 87% of these infants had salivary IgA concentrations on average 10 times higher that the age-related median concentration. The most prevalent pathogen identified in the ALTE infants was respiratory syncytial virus (RSV) (64%). RSV was also identified in all subjects with bronchiolitis. Risk factors for SIDS were assessed in each group. The data indicated that the ALTE infants diagnosed as 'near-miss' SIDS were a relatively homogeneous group, and most likely these ALTE infants and SIDS represent associated clinical outcomes. The study identified exposure to cigarette smoke and elevated salivary IgA concentrations as predictors of an ALTE. The study findings support the hypothesis of mucosal immune dysregulation in response to a respiratory infection in some infants with an ALTE. They provide a plausible explanation for certain SIDS risk factors. The underlying patho-physiological mechanism of proinflammatory responses to infections during a critical developmental period might be a critical factor in infants who have life-threatening apnoea or succumb to SIDS. The study raises the possibility of using salivary IgA to test infants who present with mild respiratory infections to identify a substantial number of infants at risk of developing an ALTE or SIDS, thus enabling intervention management to prevent such outcomes.

Update on sudden infant death syndrome

PURPOSE OF REVIEW

With the introduction of the Back to Sleep campaign by the American Academy of Pediatrics in 1992, the incidence of Sudden infant death syndrome has decreased by almost 50%. Despite this success, SIDS continues to be the most common cause of unexplained infant death in Western countries. This article will briefly review the definition, etiology, and risk factors of SIDS. Attention will then focus on ways to target specific associated risk factors and at risk populations to promote a continued downward trend in the number of SIDS deaths.

RECENT FINDINGS

Recent literature in SIDS research has focused on identifying infants at continued risk for SIDS. Children attending child care centers have an increased risk for SIDS, which is of particular concern as the number of infants in child care continues to rise. The reasons for this, along with strategies to decrease this risk, will be reviewed. In addition, the SIDS rate among black infants continues to be more than twice that of white infants. A review of the reasons for this disparity and ways to intervene through targeted campaigns will be discussed. Recent data has also suggested that the prevention of SIDS should not be an indication for use of home cardiorespiratory monitoring. The use of home monitoring may be warranted for some infants and will be reviewed.

SUMMARY

Our jobs as pediatricians should be to ensure that the incidence of SIDS continues to decline. This can be done through parent education at each and every well child visit, lobbying to enforce state law to implement SIDS education campaigns for child care centers and within African-American communities, and continued review of the most current literature in SIDS research to keep ourselves current and well informed.