Drinking Water and Infectious Disease: Establishing the Links

Abstract

Water has a special significance for epidemiologists, whose very science was founded by John Snow's studies of waterborne cholera in nineteenth century London. Many people believe that such outbreaks have been consigned to history, and that water treatment and disinfection have stopped waterborne disease transmission in developed countries once and for all, except on odd occasions when things go wrong. This book will correct that impression; research in the past decade, by some of the authors collected here, has shown that populations in developed countries, drinking water which has been treated to meet WHO guidelines and EU or USEPA quality standards, can still experience a substantial amount of waterborne enteric infection and disease. The book is based on an OECD expert group meeting held in July 2000 to address the need for international coordination for improved surveillance and outbreak investigation. The focus is on issues of epidemiological methodology, with sections on surveillance systems, on outbreak investigation, and on the investigation of sporadic disease. Nearly half the authors are public officials. That sounds like a recipe for something dry and dreary, but the book makes exciting reading. This is partly because the discussions of methodology are liberally illustrated with cases from the field, and good accounts of epidemiological detective work always impart some of the thrill of the chase. Most of the chapters are also well written, or at least adroitly edited to be very readable. It is unusual for practitioners to be good writers, and this group has done well. The theoretical parts, such as the listing of the factors to bear in mind when designing a surveillance system or an outbreak investigation, should be valuable for teaching. Written as they are by practitioners (or by ex-practitioners who have defected to academia) they are rooted in actual practice but trenchant in describing the weaknesses of current arrangements. Statements such as, ‘The surveillance systems of many European countries are incapable of detecting waterborne disease’ and ‘There is very little evidence that coliform monitoring is predictive of disease associated with drinking water’ bring one up short. Clever ideas, such as the suggestion that one ask the cases in a case-control study to suggest their friends as controls, enliven the text. There are accounts of most of the significant events in the field in the past decade, such as the Milwaukee cryptosporidiosis epidemic with over 400 000 cases, and the court case following the outbreak in Torbay, UK. The cause of the former and the outcome of the latter are given in the book, but I mustn't spoil those stories for you. Others, such as Pierre Payment's prospective studies in Canada, are mentioned in passing and the relevant references are cited. The discussion of recent findings about Cryptosporidium is particularly good on what we don't yet know about it. The book thus offers an effective update on recent developments in the study and prevention of waterborne disease. The shortcomings of the book are minor. The discussion of surveillance system design does not describe how parallel systems can be used to increase sensitivity, or the relative advantage of sentinel versus exhaustive systems; there is no mention of the E. coli O157 outbreak in Walkerton, Ontario; and, though there is one chapter about the developing countries, there is no account of the community-based surveillance systems for detecting cases of guinea-worm disease in Africa, whose effectiveness under difficult conditions—remote and inaccessible communities, severe resource constraints, illiterate frontline workers, multiple language communities, and so on—puts the health authorities of Milwaukee to shame.