Table 3. Methodological Recommendations for Future Studies of Persistent COVID-19 Symptoms.

Category	Recommendations
Study population	Report underlying comorbidities (based on WHO56 and CDC57 guidelines), including hypertension, type 2 diabetes, obesity, chronic kidney disease, cancer, compromised immunity, COPD, heart conditions, and smoking
	Report prevalence of symptoms before COVID-19 infection
	Report severity of COVID-19 illness: asymptomatic or mild, moderate, severe, and critical using standard COVID-19 symptom severity scales (eg, WHO56)
	Report patient care settings, including inpatient (ICU/non-ICU), outpatient, and individuals not seeking treatment
	Use patient flowchart similar to STROBE diagram58 reporting the number of patients eligible, excluded, and lost to follow-up (with reasons)
	Include a comparable cohort of individuals without COVID-19 for comparison
Recruitment strategy	Recruit patients consecutively and indicate reasons for any nonconsecutive enrollees
Follow-up	Define time zero, with universal reporting of time from initial diagnosis or first symptom onset
	Report mean length of follow-up, including SD and range
	Measure and report outcomes longitudinally at fixed intervals (at least monthly)
Exposure measurement	Report COVID-19 diagnosis based on PCR test or test of equivalent specificity
	Provide name of specific confirmatory test, along with its sensitivity and specificity
Outcomes of interest	Refer to established core outcome sets (eg, COMET Initiative59 or WHO COVID-19 Working Group60) to identify relevant symptoms and outcome definitions for a disease category
Outcome measurement	Report methods of collecting outcome information (eg, phone vs in-person); passive methods (eg, EHR) discouraged for symptoms unlikely to require specific treatment or be passively reported (eg, fatigue and neurocognitive outcomes)
	Include operational definitions for each measured symptom
	Report severity of symptoms (mild, moderate, severe, and/or critical)
	Report number of symptoms experienced by each patient
	Use validated instruments to measure symptoms when available (eg, Chalder Fatigue Scale or Fatigue Severity Scale to measure fatigue, 36-Item Short Form Survey or EuroQol questionnaires to measure quality of life) (Table 1)
	Include questionnaire used to measure symptoms (when applicable) in supplementary material
Results	Stratify symptom frequency and severity by baseline severity of COVID-19 infection and/or patient care setting and patient characteristics (eg, age, comorbidities, and race/ethnicity)

Abbreviations: CDC, Centers for Disease Control and Prevention; COMET, Core Outcome Measures in Effectiveness Trials; COPD, chronic obstructive pulmonary disease; EHR, electronic health record; ICU, intensive care unit; PCR, polymerase chain reaction; WHO, World Health Organization.