Signs and outcomes from three.32 million individuals examined for SARS-CoV-2

A study recently published in October 2020 on the preprint server medRxiv * shows that extensive studies are required on the clinical features and results of COVID-19 on a national and international level. This is important in order to shape interventions and optimize the use of resources to contain and deal with a second wave of the pandemic.

Differences in the testing strategies

As the world emerged from the shadow of the first wave, most countries relied on testing and case isolation with contact tracing and quarantine. However, there is a huge difference in the way these strategies are implemented from country to country. Some do mass tests on whole populations. Others do more targeted tests.

While the initial shortage of tests has largely been overcome, with the second wave it can happen that the test capacity is again stretched beyond its limits. In addition, there is a lack of information about the clinical profile of the disease and its outcomes in the tested and positive patients. Population-based cohort tests are rare among the numerous reports now available.

Large differences in the proportion of positive tests

The current study aims to identify the social, demographic and clinical characteristics at the time the patient was tested for COVID-19 and the results after a positive test. This is important in understanding the actual severity of the disease and in predicting the spread of the virus and future health care stresses.

The analysis includes over 3.3 million people, of whom ~ 219,000 tested positive between January and June 2020. Patients from three different continents were included.

The comparison of the test numbers with the positives showed that the proportion of positives among those tested was between 2.3: 100 and 31.2: 100. There has been a clear trend over time that the ratio from February to April was much higher (50: 100 in April) than 6.8: 100 in May / June 2020.

Basic comorbidities 30 days before the index date among SARS-CoV-2-tested and tested + cohorts in databases of various settings

Sociodemographic Factors

Most of the participants were adults under 64 years of age, with 20% to 48% being over 65 years old depending on the study. The proportion of women fluctuated between 52% and 64% in almost every study included. The positives usually had a higher prevalence of chronic illness, particularly heart disease and high blood pressure, at ~ 42% and ~ 60% in the positive group versus 19% and ~ 20% in the tested group. Obesity was also more common in the positives with ~ 44% than in 31% in the group tested.

Previous studies have also shown that high blood pressure, heart disease, and diabetes are more common in people with COVID-19.

The symptoms most commonly reported in the group tested were cough, fever, and shortness of breath. Their prevalence was still higher in the positives, and patients were hospitalized for some reason.

COVID-19 symptoms on the index date among SARS-CoV-2-tested and tested + cohorts in databases of various settings

COVID-19 symptoms on the index date among SARS-CoV-2-tested and tested + cohorts in databases of various settings

Results below positives

30 days after diagnosis, ~ 4% to ~ 38% of positives in various studies were hospitalized. The proportion of deaths during this period was between ~ 9% and ~ 11%. The results tended to improve over time. The hospital stay rate of 45% in March 2020 fell to ~ 14% by May and the 30-day death rate decreased from 11% to ~ 1% over the same period. Positive pneumonia patients accounted for ~ 4% to ~ 22% of the total during this period, while 1% to 12% developed acute respiratory distress syndrome (ARDS).

Other complications

Patients who tested positive for COVID-19 had a risk of sepsis between 0.6% and ~ 5%. In this group, the most common kidney complication was acute kidney injury in up to ~ 8%, with 1.5% requiring dialysis.

When considering the total combined cardiovascular event outcome, 0.2% to 5% of these patients were affected. Venous thromboembolism (VTE) was observed in 0.2% to ~ 2%.

Reasons for observed differences

The large inequality in the proportion of positive results shows the differences in test strategies and practices as well as in test coverage. The study also found a significant change in tests over time through May / June 2020.

Although it is now beyond doubt that COVID-19 disproportionately affects the elderly and males, most of the people tested and positive were female and under 64 years of age. Reasons attributed to this phenomenon include increased exposure of women in the workplace, such as in hospitals or nursing homes, or the fact that women may seek tests more often.

Chronic illnesses are more common in the positives, possibly because they are more likely to be tested for those illnesses, or because they or the treatment for these conditions promote SARS-CoV-2 infection.

Serious and critical illness

The analysis shows a total spectrum of severe illnesses that require hospitalization in 4% to 38% of the positives. These patients were also more likely to develop ARDS and various other systemic complications. This is in line with other reports, such as those from the U.S. Centers for Disease Control and Prevention (CDC).

However, as more cases are diagnosed with less severe illness, the proportion of cases in the hospital is likely to decrease. The high mortality of 4% to 11% within a month of the first positive test may be due to the numbers coming from the highest pandemic months.


This is the largest group of patients reported COVID-19 tests, reviews, and baseline traits. The investigators used 12 databases from three continents.

The authors conclude, "Our study suggests that symptoms such as cough and fever remain important disease features that predict a positive test." However, these are somewhat non-specific symptoms and their value in distinguishing between COVID-19 and other diseases like influenza must be carefully studied in future studies.

An important side effect was that an indirect assessment of the population could be performed with a negative COVID-19 test that comprised ~ 93% of the total cohort tested. Therefore, they are responsible for the differences in patient characteristics and results between the tested and positive results.

The challenge for health authorities is to ensure adequate testing capacity for the second wave and to keep the percentage of positives low below 5% to ensure the pandemic stays under control.

* Important NOTE

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.

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