Introduction

It is a central, if unspoken, tenet in medicine that interventions which alleviate disease only do good. For non-transmissible diseases this is certainly true. However, over the past decade, the quantitative study of transmissible diseases has shown several examples where the treatment of individuals has consequences on the untreated proportion of the population which may lead to overall disease being increased by the intervention. Whilst conflicts in resource allocation, between, for example, providing kidney machines or hip replacements, are discussed fairly widely, conflicts between treating an individual and increasing the risk of disease to those untreated receive very little attention. The purpose of this review is to raise these issues for discussion.

When evaluating the overall effect of a control policy on morbidity and mortality for any disease, the important considerations are the risks to individuals of infection and consequent disease, and the numbers exposed to those risks. Interventions against transmissible infections will reduce the risk of infection to some or all of the population, but may decrease or increase the risk of disease following infection and may decrease or increase the total number of people exposed to these altered risks. The risks of disease to individuals and groups within a population are, by design, always improved by interventions targetted at them, but the consequences to the remainder of the population who are not directly targetted are not guaranteed to be beneficial, and it is from this inequality that conflicts between population and individual benefits arise.

I begin by outlining the epidemiological differences between transmissible and non- transmissible diseases, for it is in these differences that the conflicts have their origins.