How Do We Define Long COVID?

It’s a story that is becoming all too common: experiencing persistent symptoms after recovering from acute COVID-19 infection. Serious and even debilitating symptoms, such as fatigue and shortness of breath, have become infamous identifiers of post–COVID-19 condition, often called “long COVID.” However, there is still no ubiquitous definition of long COVID.

The United Kingdom National Institute for Health and Care Excellence (NICE), the World Health Organization (WHO), and the US Centers for Disease Control and Prevention (CDC) have all published definitions of post–COVID-19 condition, and there are discrepancies between their respective definitions.

Recent study findings suggest these diverging definitions may prove problematic; the WHO definition was so broad that even individuals who never contracted COVID-19 could be classified as long COVID patients.

A new literature review, published in JAMA Network Open, sought to describe how post–COVID-19 condition has been defined in studies on the topic. From February 1, 2020, to October 26, 2022, the descriptive analysis included studies with information on long COVID.

After identifying 295 studies that met inclusion criteria, the investigators extracted definitions of post–COVID-19 condition, country where the study was conducted, study type, and manuscript submission date.

The included papers consisted of 134 cohort studies (45.4%), 66 cross-sectional studies (22.4%), 45 case reports or case series (15.3%), 13 case-control studies (4.4%), 2 randomized clinical trials (0.7%), and 35 studies with other designs (11.9%). Of all the studies, 167 (56.6%) were conducted in European countries.

Only 102 studies (34.6%) used 1 of the 3 public health organizations’ definitions of long COVID (56 used NICE’s, 31 used WHO’s, and 15 used CDC’s). 6 were submitted for publication before NICE released their definition of long COVID.

Of the 193 studies (65.4%) that did not follow any of these 3 definitions of post–COVID-19 condition, 129 of them (66.8%) used their own definition of long COVID, and 64 (33.2%) did not define long COVID.

The finding that 2 out of 3 studies not adhering to definitions from the NICE, CDC, or WHO suggests they may be leaving something to be desired. The study authors wrote that this diversity of long COVID definitions can lead to “considerable variation when translating findings into clinical management and cost-effectiveness assessments of interventions in patients with post–COVID-19 condition.”

A consistent definition of long COVID is long overdue and can ensure clinical trial evidence is accurately utilized to improve the treatment of patients with post–COVID-19 condition.