Emergency department visits and infections

We read with interest the article by Quach and colleagues,1 but disagree with the authors’ interpretation that the findings suggest a causal link between emergency department visits and subsequent infections. The more likely sequence of events may have been that infections in patients led to emergency department visits for nonspecific symptoms, emergency care providers did not always make the diagnosis and diagnoses were made in the subsequent week.

An essential feature of a cohort study is that patients must be free of disease at the time the exposure is assessed. In this study,1 the exposure is the emergency department visit; so, excluding infection as the cause of the emergency department visit is paramount. The authors’ method of excluding infections at the time of the emergency department visit was to examine the reason for the visit. This approach is problematic because reasons for visits often match poorly with clinical diagnoses.2 For example, a complaint of “mobility impairment” from a patient from a long-term care facility does not exclude infection as an etiology. That the emergency department visit came before the diagnosis of infection in no way establishes the direction of causality — this was described by Bradford Hill in 1965 as a problem of temporality.3

An emergency department is an important site of care for residents of nursing homes, and research that suggests emergency departments may be harmful may do a disservice to patients who need such care.4 A person who got sick after visiting an emergency department may have had an illness that predated the visit. We do not dispute that any public place, including hospital emergency departments, may lead to transmission of infection, but in our opinion the evidence presented by Quach and colleagues and the methods used to gather that evidence are insufficient to support their conclusion.1