Respiratory infections and immune biomarkers of infection and inflammation in cases of Sudden Unexpected Death in Infancy (SUDI) at the Tygerberg Medico-legal Mortuary
Thesis (MMedSc)--Stellenbosch University, 2018.
ENGLISH SUMMARY: infant death syndrome (SIDS) is the leading cause of infant death in the post-neonatal stage in developing and developed countries. A diagnosis of SIDS is made after medico-legal investigations fail to demonstrate an adequate cause of death in sudden unexpected death in infancy (SUDI) cases and SIDS is diagnosed in over 60% of SUDI cases. The peak incidence of SUDI is observed when infants are aged between two to four months. It is also at this stage that infants lose their maternally acquired immunity against infections. During medico-legal investigations in SUDI cases, viruses and bacteria have been confirmed, although none of them was consistently and exclusively associated with SUDI to date. Furthermore, viral respiratory symptoms are reported in 44% of SUDI cases, but the exact role they play in the events leading up to the death of the infant remains unknown. Viral infections can either facilitate easier bacterial colonisation of the respiratory system or induce an unregulated immune response through the release of cytokines and chemokines (immune biomarkers) that lead to formation of immune complexes in lungs and other respiratory organs. This could result in the loss of functionality and ultimately death of the infant. The role played by viruses and the interaction of the immune system in the events leading to SIDI therefore require further investigation to get a clearer understanding. Objectives: The first aim of this cross-sectional, descriptive study was to characterise the respiratory viruses observed in SUDI cases investigations at the Tygerberg Medico-Legal Mortuary using the Seeplex RV15 ACE detection multiplex PCR kit. The multiplex PCR viral detection results were compared to routine shell vial culture results to determine the superior viral detection method. The second aim was to assess 16 target immune biomarkers as indicators of infection or inflammation prior to or at the time of death of an infant. Methods: Samples were collected from 183 SUDI cases admitted to the Tygerberg Medico-Legal Mortuary between July 2015 and June 2016. Swabs collected from the trachea and left and right lungs were collected for multiplex PCR detection of 15 respiratory viruses. These viral targets were human adenovirus, human bocavirus, human coronavirus 229E/NL63, OC43, human enterovirus, influenza A and B, human metapneumovirus, human parainfluenza 1-4, respiratory syncytial virus A and B and human rhinovirus A/B/C. Serum was also collected for immune biomarker testing. Tissue from both lungs were collected for shell vial culture and blood was collected for HIV 1/2 antibody testing. Microbiology routine testing included culture of heart, left and right lung swab samples. Results: The gender distribution of infants in this study was not consistent with literature. There were 93 (50.8%) females and 90 (49.2%) males, although males have been identified as being at a greater risk of SUDI than females. However, other socio-demographic risk factors for SUDI, such as the greatest risk of death being at age two to four months were consistent with literature. The detection of viruses by multiplex PCR proved to be superior to SVC as the former detected viruses in more cases than the latter. The most commonly detected virus by multiplex PCR was human Rhinovirus A/B/C, which was detected in 65 (35.5%) of the 183 cases tested. Adenovirus was the second most frequently detected virus as it was present in 18 (12.6%) of the cases tested. Parainfluenza 3, Enterovirus and RSV B were detected in 10 (5.5%), 9 (4.9%) and 7 (3.8%) cases respectively. Human metapneumovirus was not detected at all by either assay. The serum concentrations of CRP and IL-6 were significantly elevated in the serum of SUDI cases where infection was the cause death compared to cases that were diagnosed as SIDS. However, levels of IL-18 were significantly reduced in the serum of SUDI cases where infection was the cause of death compared to cases with a final cause of death classification of SIDS. Conclusion: It is possible to change the cause of death from SIDS to infection if serum immune biomarker results and multiplex PCR are used in addition to tissue histology. The current study showed that serum CRP, IL-6 and IL-18 levels can possibly be regarded as candidates for use as indicators of infectious death and these findings need to be further investigated in larger study cohorts and over longer study periods.
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