SARS-CoV-2 epidemiology in the Icelandic population

1. In this study of the incidence of SARS-CoV-2, screening of over 5% of the Icelandic population revealed a frequency of infection of nearly 1%.

2. The percentage of participants who tested positive remained stable over the course of the 20-day study, consistent with a slow spread of the virus.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Despite global implementation of lockdowns and widespread dissemination of social distancing guidelines, over 3 million people in over 200 countries have been infected with SARS-CoV-2, and over 200,000 have died from COVID-19. The Icelandic population consists of 364,000 inhabitants, and the international airport is the only major gateway onto the island. The first infection in Iceland was detected in late February, and by the end of March, over 1300 persons had tested positive. This study analyzed the spread of the virus in Iceland using a combination of targeted testing of persons deemed to be at high risk and population screening on both an open-invitation and random-sampling basis. Over 9000 individuals participated in targeted testing, and over 13% were found to be positive. Of the 13,000 persons who participated in population screening, under 1% were found to be positive. This percentage remained stable for the 20-day duration of screening, indicating relatively slow spreading of the virus in large part due to national containment measures. In the population-screening pool, nearly half of the participants reported having symptoms, most commonly rhinorrhea and cough, yet nearly half of the patients who tested positive were asymptomatic at the time of screening. Women and children experienced a lower incidence of positive results, but it is unknown whether this phenomenon was due to less exposure or greater resistance. A limitation of the study design was that those more concerned about infection were more likely to participate.

Click here to read the study in NEJM

Relevant Reading: Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2)

In-Depth [prospective cohort]: In this study of the Icelandic population, targeted testing and population screening were used to evaluate the spread of SARS-CoV-2 in light of recently implemented containment measures. Eligibility criteria for targeted testing were either the presence of symptoms (cough, fever, myalgia, dyspnea) and recent international travel or contact with an infected person. Population screening was available for all asymptomatic or mildly-symptomatic residents of Iceland. In addition to this open-invitation recruitment method, 6782 persons between the ages of 20 and 70 were directly contacted via text message, and 2283 (37.7%) participated in the study. Among those who were targeted for testing, 1221 (13.3%) tested positive for SARS-CoV-2. In contrast, only 100 of 13,080 population screening participants tested positive (0.8%; 95% confidence interval [CI], 0.6 to 1.0). 87 of 10,797 persons (0.8%; 95% CI, 0.6 to 1.0) who accepted the open invitation were positive, compared to 13 of 2283 persons (0.6%; 95% CI, 0.3 to 0.9) who were randomly selected. In the early phases of targeted testing, 65% of participants who were positive reported recent international travel compared to only 15.5% in the later phases. RNA sequencing of 643 samples revealed a novel domestic mutation, but the haplotypes present in the population largely belonged to the A1 and A2 clades.

Image: PD

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