The protective effect of breast feeding in relation to sudden infant death syndrome (SIDS): III. Detection of IgA antibodies in human milk that bind to bacterial toxins implicated in SIDS

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.

A pilot study to investigate the measurement of immunoglobulin A in Welsh Cob and Welsh Pony foals' faeces and their dam's milk

Aims: To determine if an ELISA for measurement of IgA in equine serum could be used to measure concentrations of IgA in foal faeces and to determine correlations with concentrations in the milk of the dam.Methods: Faeces from 20 Welsh Cob and Welsh Pony foals and milk from their dams were collected within 12 hours (Day 0) and at 6 days after parturition (Day 6). On Day 6, faeces could not be collected from 2/20 foals, and milk samples could not be collected from 3/20 mares. An equine IgA ELISA validated for serum and plasma was used to measure concentrations of IgA in all samples in triplicate. The precision of the assay for each sample type was determined using modified CV.Results: IgA was not detectable in 7/20 Day 0 faecal samples and in 2/18 Day 6 faecal samples. For samples with detectable IgA, the mean modified CV was 10.5 (95% CI = 6.0-15.0)% for Day 0 faecal samples, and was 6.8 (95% CI = 4.3-9.4)% for Day 6 faecal samples. Median concentrations of IgA in faeces on Day 0 were lower than concentrations on Day 6 (0.7 mg/g vs. 37 mg/g dry matter; p = 0.003). Concentrations of IgA in milk and faeces on Day 6 were statistically correlated (r = 0.59; p = 0.006).Conclusions and clinical relevance: The IgA ELISA showed acceptable precision when used to estimate concentrations of IgA in foal faeces during the first week of life, but IgA could not be detected in 37% of meconium samples collected on Day 0. This assay may be useful for investigation of the role of maternal milk IgA in the gastrointestinal tract of neonatal foals, but further assessment of both accuracy and precision of the ELISA is required.

Early life nutrition

Nutritionally, the first 1,000 days of an infant's life - from conception to two years - has been identified as a highly influential period, during which lasting health can be achieved. Significant evidence links patterns of infant feeding to both short and long-term health outcomes, many of which can be prevented through nutritional modifications. Recommended globally, breastfeeding is recognised as the gold standard of infant nutrition; providing key nutrients to achieve optimal health, growth and development, and conferring immunologic protective effects against disease. Nevertheless, infant formulas are often the sole source of nutrition for many infants during the first stage of life. Producers of infant formula strive to supply high quality, healthy, safe alternatives to breast milk with a comparable balance of nutrients to human milk imitating its composition and functional performance measures. The concept of 'nutritional programming', and the theory that exposure to specific conditions, can predispose an individual's health status in later life has become an accepted dictum, and has sparked important nutritional research prospects. This review explores the impact of early life nutrition, specifically, how different feeding methods affect health outcomes.

Quantification of vaccine-induced antipertussis toxin secretory IgA antibodies in breast milk: comparison of different vaccination strategies in women

BACKGROUND

Pertussis vaccination during pregnancy or immediately after delivery is a strategy that is increasingly being recommended to protect young infants from disease. Breast milk contains disease-specific antibodies that can contribute to the protection of young infants. The composition of breast milk could be altered by vaccination during pregnancy or near delivery. However, the quantification of these antibodies in breast milk lacks standardization.

METHODS

In this paper, sample preparation procedures and detection methods for total and antipertussis toxin (anti-PT) secretory immunoglobulin (sIg) A are proposed that can be accurately repeated and are in accordance with European Medicines Agency and Food and Drug Administration requirements. Both antibody analytes were measured in breast milk samples of lactating women obtained 8-9 weeks postpartum to compare different maternal pertussis vaccination strategies: vaccination during pregnancy, shortly after or at delivery (cocoon), less than 5 years before delivery or more than 5 years before delivery.

RESULTS

The validated immunoassays could quantitatively detect total and anti-PT sIgA in the processed breast milk samples. Significantly higher levels of anti-PT sIgA were measured in breast milk after pertussis vaccination during pregnancy or at delivery [geometric mean concentration (GMC): 2.56 and 2.15 IU/mg] in contrast to mothers with no recent (>5 years) pertussis vaccination (GMC: 0.96 IU/mg; P = 0.014 and P = 0.028).

CONCLUSION

Vaccination against pertussis in the second/third trimester of pregnancy or immediately postpartum significantly increased the levels of anti-PT sIgA in breast milk.

The relationship between maternal postpartum psychological state and breast milk secretory immunoglobulin A level

BACKGROUND

Maternal psychological state may influence the passive transfer of immune factors (e.g., immunoglobulin) via the mother's breast milk.

OBJECTIVE

The aim of this study was to determine whether a correlation exists between mothers' postpartum psychological state and their breast milk secretory immunoglobulin A (SIgA) levels.

STUDY DESIGN

Eighty-one mothers who delivered at an urban general hospital were included in our analysis. Two weeks after delivery, we measured their breast milk SIgA levels and simultaneously documented their psychological state using the Profile of Mood States (POMS), General Health Questionnaire (GHQ), and State-Trait Anxiety Inventory (STAI) scales.

RESULTS

Breast milk SIgA levels were negatively correlated with negative POMS states (tension-anxiety, depression-dejection, anger-hostility, fatigue, and confusion). A negative correlation was also observed between SIgA levels and GHQ mental health (r = -.625, P = .000), and a similar negative correlation was observed with STAI trait and state anxieties. However, no correlation existed between breast milk SIgA levels and the positive POMS state (vigor).

CONCLUSIONS

These results indicate that the maternal psychological state may affect the immune properties of breast milk.

Pathogenesis of early atherosclerotic lesions in infants

High serologic lipid levels, infections, and genetic susceptibility have been proposed as possible etiologic factors of initial atherosclerotic lesions of the coronary arteries in infancy. At a recent WHO annual meeting, it was stated that breast milk substitutes cause irreparable damage in infants. This prompted us to verify whether formula feeding and parental cigarette smoking might play a role in the pathogenesis of early atherosclerotic alterations in infancy. The major epicardial coronary arteries from 36 infants dying suddenly and unexpectedly (sudden infant death syndrome) were embedded in paraffin and serially cut for histologic examination. In 67% of the cases, multifocal coronary early atherosclerotic lesions of varying entities were detected. The alterations ranged from focal plaques with mild myointimal thickening to juvenile soft plaques reducing the arterial lumen. A significant correlation was observed between the early atherosclerotic lesions and the risk factors considered. In particular, we noted different morphologic patterns related to formula feeding and cigarette smoking. Baby formula feeding and parental cigarette smoking might have an atherogenic effect on the coronary walls as from the first months of life. The lesions appear to be larger and more diffuse when both these atherogenic factors are present.

Ethnicity, infection and sudden infant death syndrome

Epidemiological studies found the incidence of SIDS among Indigenous groups such as Aboriginal Australians, New Zealand Maoris and Native Americans were significantly higher than those for non-Indigenous groups within the same countries. Among other groups such as Asian families in Britain, the incidence of SIDS has been lower than among groups of European origin. Cultural and childrearing practices as well as socio-economic factors have been proposed to explain the greater risk of SIDS among Indigenous peoples; however, there are no definitive data to account for the differences observed. We addressed the differences among ethnic groups in relation to susceptibility to infection because there is evidence from studies of populations of European origin that infectious agents, particularly toxigenic bacteria might trigger the events leading to SIDS. The risk factors for SIDS parallel those for susceptibility to infections in infants, particularly respiratory tract infections which are also major health problems among Indigenous groups. Many of the risk factors identified in epidemiological studies of SIDS could affect three stages in the infectious process: (1) frequency or density of colonisation by the toxigenic species implicated in SIDS; (2) induction of temperature-sensitive toxins; (3) modulation of the inflammatory responses to infection or toxins. In this review we compare genetic, developmental and environmental risk factors for SIDS in ethnic groups with different incidences of SIDS: low (Asians in Britain); moderate (European/Caucasian); high (Aboriginal Australian). Our findings indicate: (1) the major difference was high levels of exposure to cigarette smoke among infants in the high risk groups; (2) cigarette smoke significantly reduced the anti-inflammatory cytokine interleukin-10 responses which control pro-inflammatory responses implicated in SIDS; (3) the most significant effect of cigarette smoke on reduction of IL-10 responses was observed for donors with a single nucleotide polymorphism for the IL-10 gene that is predominant among both Asian and Aboriginal populations. If genetic makeup were a major factor for susceptibility to SIDS, the incidence of these deaths should be similar for both populations. They are, however, significantly different and most likely reflect differences in maternal smoking which could affect frequency and density of colonisation of infants by potentially pathogenic bacteria and induction and control of inflammatory responses.

Detection of specific antibodies in cord blood, infant and maternal saliva and breast milk to staphylococcal toxins implicated in sudden infant death syndrome (SIDS)

The common bacterial toxins hypothesis of sudden infant death syndrome (SIDS) is that nasopharyngeal bacterial toxins can trigger events leading to death in infants with absent/low levels of antibody that can neutralise the toxins. The aim of this study was to investigate nasopharyngeal carriage of Staphylococcus aureus and determine levels of immunity in the first year of life to toxic shock syndrome toxin (TSST-1) and staphylococcal enterotoxin C (SEC). Both toxins have been implicated in SIDS cases. Seventy-three mothers and their infants (39 males and 34 females) were enrolled onto the study. The infants had birth dates spread evenly throughout the year. In infants, S. aureus carriage decreased significantly with age (P<0.001). Between 40% and 50% of infants were colonised with S. aureus in the first three months of life and 49% of the isolates produced one or both of the staphylococcal toxins. There was a significant correlation between nasopharyngeal carriage of S. aureus in mothers and infants in the three months following the birth (P<0.001). Carriage of S. aureus in infants and their mothers was not significantly associated with levels of antibody to TSST-1 or SEC in cord blood, adult saliva or breast milk. Infants colonised by S. aureus had higher levels of salivary IgA to TSST-1 than infants who were culture negative. Analysis of cord blood samples by a quantitative ELISA detected IgG bound to TSST-1 and SEC in 95.5% and 91.8% of cases respectively. There was a marked variation in levels of maternal IgG to both TSST-1 and SEC among cord blood samples. Maternal age, birth weight, and seasonality significantly affected the levels of IgG binding to TSST-1 or SEC. Analysis of infant saliva samples detected IgA to TSST-1 and SEC in the first month after birth; 11% of samples tested positive for salivary IgA to TSST-1 and 5% for salivary IgA to SEC. By the age of two months these proportions had increased to 36% and 33% respectively. More infants who used a dummy tested positive for salivary IgA to TSST-1 compared to infants who did not use a dummy. Levels of IgA to TSST-1 and SEC detected in the breast-milk samples varied greatly among mothers. There was a trend for infants receiving breast milk with low levels of antibody to TSST-1 or SEC to have higher levels of salivary antibody to the toxins. In conclusion, passive immunity to toxins implicated in SIDS cases varies greatly among infants. Infants are able to mount an active mucosal immune response to TSST-1 and SEC in the first month of life.

The role of bacterial toxins in sudden infant death syndrome (SIDS)

There is increasing evidence for the involvement of bacterial toxins in some cases of sudden infant death syndrome (SIDS), particularly the pyrogenic toxins of Staphylococcus aureus. This had led to the hypothesis that some SIDS deaths are due to induction of inflammatory mediators by infectious agents or their products during a period in which the infant is unable to control these normally protective responses. The genetic, developmental and environmental risk factors identified for SIDS are assessed in relation to frequency or density of mucosal colonisation by toxigenic bacteria and their effects on induction and control of inflammatory responses to the toxins.

The role of colostral antibodies in prevention of microbial infections

Mammalian colostrum offers passive protection to the newborn against a variety of microbial pathogens, in the form of specific immunoglobulin A, G and M antibodies. Sharing maternal immunological memory is in many cases vital for the infant, but may have disastrous consequences, such as involuntary transfer of disease and disturbance of the developing immune system. In most published studies, immune milk preparations are reported to be effective in the prevention of various gastroenteric infections, but not in the treatment of an established infection.

Review of risk factors for sudden infant death syndrome

Sudden infant death syndrome (SIDS) accounts for the largest number of deaths during the first year of life in developed countries. The possible causes of SIDS are numerous and, to date, there is no adequate unifying pathological explanation for SIDS. Epidemiological studies have played a key role in identifying risk factors, knowledge of which has underpinned successful preventive programmes. This review critically assesses information on the main risk factors and causal hypotheses put forward for SIDS, focusing on research published since 1994. The overall picture that emerges from this review is that affected infants are not completely normal in development, but possess some inherent weakness, which may only become obvious when the infant is subjected to stress. Initially there may be some minor impairment or delay in development of respiratory, cardiovascular or neuromuscular function. None of these is likely to be sufficient, in isolation, to cause death and, provided the infant survives the first year of life, may no longer be of any significance. However, when a compromised infant is confronted with one or more stressful situations, several of which are now clearly identified as risk factors, and from which the majority of infants would normally escape, the combination may prove fatal.

Breastfeeding in countries of the European Union and EFTA: current and proposed recommendations, rationale, prevalence, duration and trends

Recommendations suggest exclusive breast feeding for at least the first 4 to 6 months after birth. Paradoxically, an overwhelming proportion of breast feeding (BF) data in Europe refers to all BF, i.e. not only exclusive but also partial BF (including formula, juices, water, sweetened water etc). This makes it difficult to estimate to what extent the recommendations are met. There is currently strong evidence for recommending exclusive breast feeding for at least 6 months. Exclusive BF has progressively gained scientific support. Prevention of infections, allergies and chronic diseases and a favourable cognitive development are highlighted in the recent scientific literature. Further long-term studies on the effects of BF on prevention of chronic disease in the adult are needed. Great differences exist in BF prevalence and duration both within and between European countries. Trends point towards higher prevalence and duration, with some exceptions. Young mothers breast feed less than older mothers; single and/or less educated mothers breast feed less than married mothers with more education. However, inefficient and unreliable monitoring systems prevail, and the data are scarce, not only on exclusive BF but also on demographic, socio-economic, psychosocial and medical determinants of BF patterns. National BF coordinators have not been appointed in many countries, and only every second country has promotion of BF incorporated into their national plan of action for nutrition.

CONCLUSIONS

Efficient surveillance systems, comparable across Europe and using common definitions and methodology, need to be developed. These should include determinants of breast feeding. A European consensus conference should urgently be organised, in which strategies for successful promotion of exclusive BF should be particularly considered. There is now strong evidence for a recommendation to breast feed exclusively for about 6 months, which is more than the duration recommended previously.

Long-time persistence of superantigen-producing Staphylococcus aureus strains in the intestinal microflora of healthy infants

Staphylococcus aureus has been isolated at an increasing rate from infants' stools during the last decades, but it is not known whether this species can colonize and persist in the intestinal microflora. To investigate this, 49 Swedish infants were followed prospectively from birth until 12 months of age. S. aureus was identified in a rectal swab obtained 3 d after delivery and in quantitative cultures of fecal samples collected at 1, 2, 4, and 8 weeks and at 6 and 12 months of age. A random amplified polymorphic DNA (RAPD) method was developed to distinguish individual S. aureus strains from one another and the strains were tested for production of enterotoxins A-D and TSST-1. By 3 days of age, 16% of infants had S. aureus in their intestines, which increased to 73% by 2-6 months, whereafter it decreased slightly to 53%. At the same time S. aureus population counts in colonized infants declined from an average 10(6.8) CFU/g feces during the first months of life to 10(4.0) CFU/g feces by 12 months. Colonized infants usually harbored one or two S. aureus strains in their microflora for long periods of time. Few strains were transient passengers and the median time of persistence of S. aureus strains in the microflora was several months. Of the 75 S. aureus strains identified, 43% produced one or more toxins: 13% SEA, 7% SEB, 23% SEC, 4% SED, and 11% TSST-1. Altogether, 47% of the investigated infants were colonized by a toxin-producing S. aureus during their first year of life. Despite this they were apparently healthy and did not have more gastrointestinal problems than noncolonized infants. This report is the first to show that S. aureus may be a resident member of the normal intestinal microflora in infancy.

Sudden infant death attributed to peracute pulmonary infection: two autopsy cases

This report describes two autopsy cases of sudden infant death attributed to peracute pulmonary infection in which possible causative microorganisms could be identified despite only minor pathological findings. Both babies were 5-month-old boys, who had no symptomatic disorders and were found dead in bed. Their main macropathology was inflated heavy lungs with patchy bleedings. One case showed a pulmonary histopathological finding suggestive of viral infection, and adenovirus DNA was detected from the intrabronchial fluid. In the second case, pulmonary histopathology was a feature of early inflammatory reaction involving focal necrosis with some neutrophil infiltration and many intra-alveolar macrophages containing gram-positive cocci, and Staphylococcus aureus was identified in venous blood culture. These findings significantly support the presence of pathogenic microorganisms in sudden infant death.

The role of breastfeeding in sudden infant death syndrome

The objective of this article is to review the literature regarding the risk of sudden infant death syndrome (SIDS) in bottle-fed infants compared to those that are breastfed. A meta-analysis and qualitative literature review were performed. Cohort and case-control studies were included if they met a minimum SIDS definition and presented data allowing calculation of an odds ratio (OR). Twenty-three studies were included in the meta-analysis. The studies were heterogeneous, and a majority (14) were of "fair" or "poor" quality. Crude ORs from 19 individual studies favored breastfeeding as protective against SIDS. The combined analysis indicated that bottle-fed infants were twice as likely to die from SIDS (pooled OR = 2.11; 95% CI 1.66-2.68). The results of the analysis show that there is an association between bottle-feeding and SIDS, but this may be related to confounding variables.

Immunological evidence for a bacterial toxin aetiology in sudden infant death syndrome

Toxin-specific antibodies to clostridial, enterobacterial and staphylococcal toxins implicated in sudden infant death syndrome were studied in sera from sudden infant death syndrome infants and a comparison group of infants (babies with phenylketonuria). The results indicated a higher proportion of sera from sudden infant death syndrome infants contained IgA that bound to clostridial and enterobacterial toxins but a higher proportion of sera from the phenylketonuria comparison group contained IgA that bound staphylococcal toxins. The higher proportion of serum samples with IgG and IgM in the healthy comparison babies serum probably indicated immunity in this group of babies to these toxins. The effect of gender and age had a minimal effect on the incidence of these antibodies. The presence of toxin-specific antibodies in sudden infant death syndrome and the of comparison infants suggests that all infants are exposed to these toxins and most babies successfully overcome the toxic challenge. Some infants with predisposing risk factors (temperature change, smoking, infection, immune development, sleeping position, etc.) that could affect the baby's immune competency could succumb to these and possibly other toxins. This immunological evidence further strengthens the view that bacterial toxins are a significant cause of sudden infant death syndrome.

The role of infection in sudden infant death syndrome

Studies on the potential role of infectious agents in sudden infant death syndrome (SIDS) have been published over the years in a variety of journals. The aim of this special issue of FEMS Immunology and Medical Microbiology is to bring together a group of the most recent studies from Europe, Australia and Canada which cover epidemiology and laboratory studies examining hypotheses relating to infection and inflammation in SIDS. The articles in this issue examine evidence for the involvement of specific micro-organisms in SIDS and the problems relating to experimental studies on infection in relation to the underlying pathology of these deaths. There is an update on the evidence for the common bacterial hypothesis proposed in 1987 examining risk factors identified in epidemiological studies, particularly how the prone sleeping position could affect bacterial colonisation or induction of toxins. Evidence for induction of inflammatory responses in SIDS infants is reviewed and the relation of these responses to mechanisms proposed as causes of death assessed. Factors found to be associated with reduction of the risk of SIDS (breast feeding and immunisation) are examined in relation to some of the toxigenic bacteria implicated in these deaths. Finally, the high incidence of SIDS in some ethnic groups is examined as a potential model to investigate the contributions of genetic, environmental and cultural differences to susceptibility of infants not only to SIDS but to serious respiratory tract infections.