Study design

The CORFU study is a longitudinal multiple cohort study that aggregates data of seven existing Dutch COVID-19 cohorts, prospectively complemented with routinely collected outcome data on long COVID-19, with a maximum follow-up of 24 months after initial infection. Data will be collected between 1 October 2021 and 31 December 2022.

All cohorts were initiated and designed to conduct COVID-19 research. Six cohorts will collect data according to their individual clinical focus (figure 1). In addition, participants from the community-based POPulation health impact of the COVID-19 pandemic (POPCOrn) cohort will serve as a control group as this cohort partly consists of controls who did not suffer from COVID-19. However, at present, many of the POPCOrn participants could have suffered from (mild) COVID-19. Therefore, all POPCOrn participants will be asked repeatedly to report whether or not they suffered from (confirmed of suspected) COVID-19 and only the participants who did not suffer from COVID-19 will serve as a control. In the POPCOrn cohort, similar outcome data will be collected as in the other participating cohorts. As CORFU is open to new collaborations, it is likely that additional cohorts will join CORFU in the future. Participation of new cohorts will be reported when presenting the CORFU study findings.

Overview of the participating COVID-19 cohorts in the CORFU study. The source population included in the individual cohorts is an estimate as of May 2022. The total number of CORFU study participants might not add up to the total source population (n=12 631) due to non-survivors, participants included in multiple cohorts and participants who might not want to participate in the CORFU study. *At the time of manuscript preparation, prospective inclusion is ongoing in five cohorts: Adelante, CAPACITY-COVID, DC&TC, ELVIS and MaastrICCht cohort. CAPACITY-COVID, Cardiac complications in patients with COVID-19 cohorts; CORADS, COVID-19 Reporting and Data System Score; COVAS, Bernhoven Early detection of Vascular damage after COVID-19 cohort; DC&TC cohort, Dutch COVID and Thrombosis Consortium cohort; ELVIS, ZuydErLand COVID-19 regiStry; ICU, Iintensive care unit; MaastrICCht, Maastricht Intensive Care COVID cohort; NSAID, non-steroidal anti-inflammatory drug; POPCOrn, POPulation health impact of the COVID-19 pandemic; PROMS, Patient-Reported Outcome Measures; VTE, venous thromboembolic.

The cohort-specific follow-up measurements will be complemented by a repeatedly administered CORFU questionnaire covering the full array of long COVID symptoms, health-related quality of life effects and their key determinants. Furthermore, (clinical) data that have already been collected in the participating cohorts during the acute COVID stage will be used to investigate the CORFU study aims.