Difficulties in interpretation of post-mortem microbiology results in unexpected infant death: evidence from a multidisciplinary survey

Identification of bacterial pathogens in sudden unexpected death in infancy and childhood using 16S rRNA gene sequencing

Background

Sudden unexpected death in infancy (SUDI) is the most common cause of post-neonatal death in the developed world. Following an extensive investigation, the cause of ~40% of deaths remains unknown. It is hypothesized that a proportion of deaths are due to an infection that remains undetected due to limitations in routine techniques. This study aimed to apply 16S rRNA gene sequencing to post-mortem (PM) tissues collected from cases of SUDI, as well as those from the childhood equivalent (collectively known as sudden unexpected death in infancy and childhood or SUDIC), to investigate whether this molecular approach could help identify potential infection-causing bacteria to enhance the diagnosis of infection.

Methods

In this study, 16S rRNA gene sequencing was applied to de-identified frozen post-mortem (PM) tissues from the diagnostic archive of Great Ormond Street Hospital. The cases were grouped depending on the cause of death: (i) explained non-infectious, (ii) infectious, and (iii) unknown.

Results and conclusions

In the cases of known bacterial infection, the likely causative pathogen was identified in 3/5 cases using bacterial culture at PM compared to 5/5 cases using 16S rRNA gene sequencing. Where a bacterial infection was identified at routine investigation, the same organism was identified by 16S rRNA gene sequencing. Using these findings, we defined criteria based on sequencing reads and alpha diversity to identify PM tissues with likely infection. Using these criteria, 4/20 (20%) cases of unexplained SUDIC were identified which may be due to bacterial infection that was previously undetected. This study demonstrates the potential feasibility and effectiveness of 16S rRNA gene sequencing in PM tissue investigation to improve the diagnosis of infection, potentially reducing the number of unexplained deaths and improving the understanding of the mechanisms involved.

Post-Mortem Microbiology: Retrospective Analysis of Infections Caused by Enterococcus Strains

Post-mortem microbiological tests are one of the basic methods for diagnosing the etiology of infections in forensic pathology. One of the major groups of microorganisms abundant in various parts of the human body during life and after death is Enterococcus spp. Depending on the area of the body involved and the patient’s condition, enterococci can be considered to be a microbiome, transient flora or a pathogen responsible for infection. The data used for the analysis were 12 medico-legal autopsy and microbiological reports. Enterococcus spp. was isolated in 10 out of 12 cultures of blood samples collected post-mortem. The abdominal origin of enterococci in the blood was detected in 8 cases. The non-abdominal origin of enterococci in the blood was associated with a skin and soft tissue infection, purulent pneumonia and infective endocarditis. These results suggest that enterococci may be considered a cause of severe infections and with high likelihood. Microbiological cultures are a valuable source of information for helping to confirm the cause of infection. Interpretation of the results of post-mortem examinations must be carried out on the basis of data collected before and after death with the participation of specialists from various fields.

Characterising Post-mortem Bacterial Translocation Under Clinical Conditions Using 16S rRNA Gene Sequencing in Two Animal Models

Sudden unexpected death in infancy (SUDI) is the sudden and unexpected death of an apparently healthy infant occurring within the first year of life where the cause is not immediately obvious. It is believed that a proportion of unexplained infant deaths are due to an infection that remains undiagnosed. The interpretation of post-mortem microbiology results is difficult due to the potential false-positives, a source of which is post-mortem bacterial translocation. Post-mortem bacterial translocation is the spread of viable bacteria from highly colonised sites to extra-intestinal tissues. We hypothesise that although post-mortem bacterial translocation occurs, when carcasses are kept under controlled routine clinical conditions it is not extensive and can be defined using 16S rRNA gene sequencing. With this knowledge, implementation of the 16S rRNA gene sequencing technique into routine clinical diagnostics would allow a more reliable retrospective diagnosis of ante-mortem infection. Therefore, the aim of this study was to establish the extent of post-mortem bacterial translocation in two animal models to establish a baseline sequencing signal for the post-mortem process. To do this we used 16S rRNA gene sequencing in two animal models over a 2 week period to investigate (1) the bacterial community succession in regions of high bacterial colonisation, and (2) the bacterial presence in visceral tissues routinely sampled during autopsy for microbiological investigation. We found no evidence for significant and consistent post-mortem bacterial translocation in the mouse model. Although bacteria were detected in tissues in the piglet model, we did not find significant and consistent evidence for post-mortem bacterial translocation from the gastrointestinal tract or nasal cavity. These data do not support the concept of significant post-mortem translocation as part of the normal post-mortem process.

National registry for sudden unexpected deaths of infants and children in England: why do we need one and do families want one?

The sudden and unexpected death of an infant or child is devastating. An inability to explain why an infant or child died is difficult to accept for both families and professionals. No reliable national dataset exists to estimate precisely how many infants and children die unexpectedly each year in England. This lack of accurate epidemiological data belies the scale of this public health problem. Detailed controlled observational studies of infant deaths identifying risk factors and providing evidence-based advice for parents has seen a dramatic reduction in incidence over the last 30 years by almost 80% but greater knowledge is needed if future deaths of infants and older children are to be prevented and families optimally supported. We propose that a national registry of sudden unexpected deaths in infancy and childhood would accurately determine incidence, identify unknown risk factors and highlight good care practices, ensuring these can be standardised nationally. For such a project to be successful, however, parents must be at the heart of it. We held a consultation day between families, professionals and supporting charities (The Lullaby Trust, Child Bereavement UK, SUDC UK and CRY) to seek opinion on the desire for a registry and how best to ensure families are engaged. Here, we summarise our rationale for a registry and the feedback we received from attendees regarding their views of the proposal and the practical aspects of administering it.

Post-mortem microbiology in sudden death: sampling protocols proposed in different clinical settings

BACKGROUND

Autopsies, including minimally invasive autopsies, are a powerful tool for determination of the cause of death. When a patient dies from an infection, microbiology is crucial to identify the causative organism. Post-mortem microbiology (PMM) aims to detect unexpected infections causing sudden deaths; confirm clinically suspected but unproven infection; evaluate the efficacy of antimicrobial therapy; identify emergent pathogens; and recognize medical errors. Additionally, the analysis of the thanatomicrobiome may help to estimate the post-mortem interval.

AIMS

The aim was to provide advice in the collection of PMM samples and to propose sampling guidelines for microbiologists advising autopsy pathologists facing different sudden death scenarios.

SOURCES

A multidisciplinary team with experts in various fields of microbiology and autopsies on behalf of the ESGFOR (ESCMID - European Society of Clinical Microbiology and Infectious Diseases - study group of forensic and post-mortem microbiology and in collaboration with the European Society of Pathology) developed this narrative review based on a literature search using MedLine and Scopus electronic databases supplemented with their own expertise.

CONTENT

These guidelines address measures to prevent sample contamination in autopsy microbiology; general PMM sampling technique; protocols for PMM sampling in different scenarios and using minimally invasive autopsy; and potential use of the evolving post-mortem microbiome to estimate the post-mortem interval.

IMPLICATIONS

Adequate sampling is paramount to identify the causative organism. Meaningful interpretation of PMM results requires careful evaluation in the context of clinical history, macroscopic and histological findings. Networking and closer collaboration among microbiologists and autopsy pathologists is vital to maximize the yield of PMM.

Testing for Infectious Diseases in Sudden Unexpected Infant Death: A Survey of Medical Examiner and Coroner Offices in the United States

OBJECTIVES

To determine interoffice variability in routinely performed sudden unexpected infant death (SUID) postmortem studies for infection and to assess availability and perceived utility of various tests of infectious diseases.

STUDY DESIGN

Online surveys were sent to all 154 offices of US medical examiners and coroners serving populations >300,000 people. Surveys included a set of potential laboratory tests for infectious disease. Respondents were asked to select which tests were available in their offices, and which tests were performed routinely in SUIDs vs which tests should be performed routinely.

RESULTS

Of the 45 complete responses, 4.4% did not routinely perform histology, 8.9% did not routinely perform viral studies (ie, culture or molecular diagnostics), 22.2% did not routinely perform blood cultures, 26.7% did not routinely perform lung bacterial cultures, and 44.4% did not routinely perform cerebrospinal fluid cultures.

CONCLUSIONS

Our findings suggest that there is considerable interoffice variability with testing for infectious diseases in SUIDs. This appeared to be largely the result of a perceived lack of testing utility rather than a lack of test availability. Evidence-based practice guidelines regarding the interpretation of microbial testing results, as well as common testing protocols/algorithms, may lead to more accurate and standardized data, thus improving SUID investigation and surveillance.

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.

Immunohistochemical expression of inflammatory markers in sudden infant death; ancillary tests for identification of infection

Aims

Sudden unexpected death in infancy (SUDI) investigation requires extensive ancillary investigations, the results of which, such as postmortem microbiology, can be difficult to interpret. Markers of an inflammatory response, including interleukin 6 (IL-6), c-reactive protein (CRP) and cellular adhesion molecules are elevated in infections, yet little attention has been paid to their assessment after death. This study investigates the role of inflammatory markers in SUDI autopsies for determining cause of death.

Methods

Cases of SUDI over a 14 year period were identified from an autopsy database and 100 cases were selected for immunohistochemical staining of heart and liver for IL-6, CRP, P-selectin, VCAM-1 and ICAM-1 (CD54), with staining patterns compared between five groups, including infectious and unexplained SUDI.

Results

There were significant differences between groups. Cases of histological infection demonstrated strongly positive hepatocyte CRP and ICAM-1 expression and increased myocardial staining for CRP. Half of trauma-related deaths demonstrated diffuse hepatic CRP expression but without myocardial CRP staining. Staining of unexplained SUDI cases were predominantly negative, apart from a subgroup in whom Escherichia Coli was identified, who had increased expression of hepatic IL-6.

Conclusions

There were distinct patterns of organ-specific CRP and ICAM-1 expression in SUDI by cause of death. These markers of inflammation were rarely present in unexplained SUDI suggesting either a non-inflammatory cause of death or a failure to mount an effective acute phase response. Immunohistochemical staining offers potential to identify infection-related deaths and provides insight into SUDI mechanisms.

Peptide sharing between Bordetella pertussis proteome and human sudden death proteins: a hypothesis for a causal link

AIM

To explore the molecular basis of the relationship between Bordetella pertussis infection and sudden death.

METHODS

B. pertussis proteins were analyzed for amino acid sequence identity to a set of 67 human proteins that, when altered, have been associated with sudden death.

RESULTS

More than 82,000 pentapeptides are shared between B. pertussis proteins and sudden death-associated antigens.

CONCLUSION

Results suggest that a possible link between B. pertussis infection and sudden death might be represented by potential immunological cross-reactions occurring between B. pertussis proteins and human proteins associated to sudden death.

[Post-mortem microbiology analysis]

Post-mortem microbiology is useful in both clinical and forensic autopsies, and allows a suspected infection to be confirmed. Indeed, it is routinely applied to donor studies in the clinical setting, as well as in sudden and unexpected death in the forensic field. Implementation of specific sampling techniques in autopsy can minimize the possibility of contamination, making interpretation of the results easier. Specific interpretation criteria for post-mortem cultures, the use of molecular diagnosis, and its fusion with molecular biology and histopathology have led to post-mortem microbiology playing a major role in autopsy. Multidisciplinary work involving microbiologists, pathologists, and forensic physicians will help to improve the achievements of post-mortem microbiology, prevent infectious diseases, and contribute to a healthier population.

Clinicopathological features of sudden unexpected infectious death: population-based study in children and young adults

INTRODUCTION AND OBJECTIVES

Infectious diseases are one of the major causes of sudden death, but data of sudden unexpected death from infectious diseases (SUDID) are sparse in children and young people. The aim of this study is to analyse their epidemiological, clinical, pathological and microbiological characteristics.

METHODS

Population observational study of all deaths due to infectious diseases in people aged 0-34 years in Biscay between 1991 and 2010. The data of Mortality Register and Forensic Pathology Service were analysed. The SUDID cases in which a forensic autopsy was performed were identified.

RESULTS

There were 56 SUDID cases (16% of the all sudden deaths). Myocarditis (n=20) and acute bacterial bronchopneumonia/pneumonia (n=18) were the most frequent causes, followed by meningococcemia (n=5) and viral pneumonia (n=4). A chronic co-morbid condition (mainly drug abuse in young people and moderate low birth weight in infants) was recorded in one-third and prodromal symptoms in two-thirds. Seventeen young people had consumed illegal drugs and/or methadone. In 17 of the 23 autopsies where microbiological analyses were performed, the organism responsible was identified. The incidence of SUDID was 0.6/100000 inhabitants/year, representing 5% of all deaths from infectious diseases. SUDID rate was 1.87 times higher in males than in females. The highest incidence occurred in infants (3.7).

CONCLUSIONS

SUDID is infrequent, but it represents a significant proportion of all sudden deaths in children and young people. The relationship between methadone and bronchopneumonia is noticeable. This article stresses the importance of microbiological analyses in SUDID. Investigation based on forensic pathology provides useful epidemiologic, clinico-pathological and microbiological information for prevention of infectious diseases.