Travel History Should Not Be the “Fifth Vital Sign” Even Amid COVID

In a recent Ideas and Opinions article in Annals (1), several authors use the recent emergence of coronavirus disease 2019 (COVID-19) to outline the limited impact of travel restrictions and argue the merits of an intriguing strategy: travel as a “fifth vital sign.”

The logic is straightforward. Travel restrictions and screening may have limited effects on disease containment due to clinically silent incubation periods and variation in the symptoms that emerge. Even in the setting of nonspecific symptoms, COVID-19 and other infections (e.g., Ebola, SARS), can be linked to specific geographic areas—a fact that can help trace patients and enable implementation of infection control measures. As the authors put it, together with temperature, heart rate, respiratory rate, and blood pressure, a travel vital sign could “help us assess a patient's health status, triage the patient to appropriate care, determine potential diagnoses, and predict recovery” related to novel infectious diseases (1).

On the basis of this line of reasoning, the Annals authors pose a thought-provoking question: Should travel be the fifth vital sign? As much value as travel histories possess, it’s hard to imagine any response to that question except a decided “no.” Among a set of reasons, two stand out.

First, the benefit of clinical travel histories depends on—and potentially is muted by—broader infectious disease policy. Take our early experience with COVID-19 in Seattle, the epicenter of the U.S. outbreak. Amid national guidelines and policy directing travel bans toward China, many here were initially perplexed by cases diagnosed “in community” among individuals without travel history there. Viral phylodynamics would later confirm what some have marked as a missed policy opportunity: to implement early travel restrictions on other Asian and European countries that were also reporting early COVID-19 outbreaks at the time, thereby helping those strains enter and spread in the Pacific Northwest. We knew, even without travel vital signs, where individuals had traveled to, but guidelines and policy did not drive attention and resource there.

Second, and more fundamentally, it’s not clear that travel histories should even be framed alongside vital signs. In the setting of an infectious disease outbreak, the utility of a travel history lies in its specificity, that is, the potential precision with which it can create epidemiologic links to a geographic area and rapidly drill down on certain diagnoses. Contrast that with the traditional vital signs of temperature, heart rate, respiratory rate, and blood pressure, which are notoriously imprecise and nonspecific.

For instance, meeting SIRS criteria due to abnormal vital signs might be a powerful signal that “something is off.” But it’s not nearly as useful for identifying what that something is – a key part of the reason the medical community has shifted away from the vital sign-based SIRS criteria toward an organ damage–based criteria for diagnosing sepsis. The same problem exists in thinking about travel history as a vital sign for serious viral infections: It is a very specific piece of information that doesn’t work well alongside nonspecific biometric measurements.

A better solution may be to simply continue the approach already adopted in clinical medicine: using vital signs to help identify patients with clinical disease, followed by focused history-taking to focus the differential. The Annals authors themselves seem to affirm this approach, promoting “a simple, targeted travel history” to “put symptoms of infection in context and trigger us to take a more detailed history, do appropriate testing, and rapidly implement protective measures” (1). Points well-taken, and ones that don’t require travel to be incorporated as a vital sign.   

Ultimately, the ongoing COVID-19 pandemic has created the opportunity to consider different solutions for address infectious disease outbreaks. The dialogue itself is good and welcome during these uncertain times. But of the strategies being considered, incorporating travel as a fifth vital sign is unlikely to be an effective or needed one.

Reference

1. Perl TM, Price CS. Managing emerging infectious diseases: should travel be the fifth vital sign. Ann Intern Med. 3 March 2020. [Epub ahead of print]. doi:10.7326/M20-0643