Through SARS-CoV-2 IgG testing of PCR positive and negative cases the study will follow the COVID-19 immune response by monitoring the SARS-CoV-2 IgG antibody levels over a period of two years. Further, risk factors will be identified by the use of the test-negative design including population controls, allowing comparison of participants with positive and negative tests, and with population controls (triangulation). Special emphasis will be on high risk groups in general and on different occupational, environmental and socio-economic groups in particular. Finally, severity of illness, deaths and the use of health care during will be assessed using national register data from Telemark and Agder.

Objectives

The main objectives are:

1. Monitor the incidence of COVID-19 and the development of the SARS-CoV-2-IgG levels of cases in Agder and Telemark over a period of two years (WP1).
2. Identify risk factors for COVID-19 by comparison of SARS-CoV-2 antibody positive and negative cases in Telemark and Agder, and comparison of these groups separately with population controls (WP2).
3. The incidence of neurocognitive symptoms and fatigue in COVID-19 patients (WP3).
4. Investigation of severity, death and the use of health care for the COVID-19 patients based on data from national registers (WP4).

The main exposures are (WP1-3):

• Infection (mild, severe) with COVID-19.
• Occupational risk factors assessed by occupational codes (ISCO88) and job exposure matrix categorisation.
• Environmental risk factors (road traffic outside bedroom window, travel by foot or bicycle alongside busy roads, and the use of a fireplaces in residential homes. Further, estimated measurements of air pollution may be linked to participants' home address.
• Socioeconomic status; age, sex, comorbidity, medication use, lifestyle factors (smoking, BMI, physical activity, others), geographic region/municipality, education and income.

Inclusion Criteria:

• Age 18 - 85 years
• Performed SARS-CoV-2 PCR test

Exclusion Criteria:

• Non-Norwegian speakers.
• Deceased
• inability to answer questionnaire due to dementia or similar conditions

Inhabitants of Agder and Telemark County in Norway fulfilling the inclusion criteria.