Risk assessment in travel medicine: how to obtain, interpret, and use risk data for informing pre-travel advice

It has been recommended that numerical risk data should be provided during the pre-travel consultation in order for travelers to make informed decisions regarding uptake of preventive interventions. In this article, we review the definitions of the various risk measures, particularly as they relate to travel health, and discuss the study designs and methodological details required to obtain each measure. Risk measures can be broadly divided into absolute risk measures (including incidence rate, attack rate, and incidence density) and risk factor measures (including relative risk, risk ratio, and odds ratio). Although there are limitations inherent to each measure, absolute risk measures estimate the baseline risk for an "average" traveler, and risk factor measures help determine whether the risks for an individual traveler are likely to be higher or lower than this average, which is determined by specific traveler and itinerary characteristics. Incremental risk considerations add additional complexity, and risk communication plus risk perception/risk tolerance have additional impact on the individual traveler's interpretation of risk measures. Travel health practitioners should be aware of the complexities, limitations, and difficulties in understanding numerical risk data, as these factors are important in travelers' acceptance or rejection of interventions offered.