INTRODUCTION

Sudden unexpected death in infancy (SUDI) is simply defined as the death of an infant that is sudden and is unexpected. If a detailed post-mortem examination fails to reveal an adequate explanation for death then the term ‘sudden infant death syndrome’ (SIDS) is used. If the autopsy does not reveal an explanation for death, but there are suspicious features, the term ‘unascertained’ is often applied. The difference between SIDS, which legal authorities will regard as natural disease, and unascertained is, therefore, related to the level of suspicion. The latter term can cause distress to parents and lead to unnecessary inquests. It should be used sparingly. In strict logic, of course, the difference between ‘I don't know’ (SIDS) and ‘I don't know’ (unascertained) is unascertained and unascertainable.

The age distribution of SUDI and SIDS is the most consistent and characteristic feature of sudden infant death. The risk of SUDI and SIDS is low in the first few days of life, the risk then rises to a peak at two to three months, followed by a rapid fall so that the condition is uncommon after six months and rare after twelve months (Fig. 1.1). This risk profile is approximately reciprocal to infant serum IgG levels, and therefore sudden death occurs when infants have least protection against common bacteria and common bacterial toxins. For this reason it is important that careful microbiological investigation is carried out in all sudden infant deaths.