Seroprevalence studies have shown their value in estimating the size and directionality of an outbreak of infectious disease, especially the current pandemic of coronavirus 2-induced severe acute respiratory syndrome (SARS-CoV-2) 2019 (COVID -19). A new study published in medRxiv* The prepress server describes the prevalence of SARS-CoV-2 antibodies in five representative regions of Germany.
Seroprevalence is the number of people in a population who test positive for a specific disease based on serology samples (blood serum).
German estimates of the number of infections in its population are mainly based on the number of compulsorily reported infections, derived from local health authorities. Once the first case was reported in January 2020, the strategy initially focused on case studies, contact tracking, and the search for infection points.
Polymerase chain reaction (PCR) detection tests of SARS-CoV-2 genetic material were performed for certain groups, such as health care workers.
As a result, estimates of viral transmission ruled out asymptomatic or mild infections, as they do not reach medical attention. The current study seeks to use population-based data on viral ear-specific immunoglobulin (Ig) G titers antigen to calculate the number of people exposed and the infection mortality rate for each age group.
This would help control the functioning of various interventions at the population level and how to prevent a further increase in incidence and set up vaccination policies.
MuSPAD sampling time per site compared to reported cases Source @RKI in Germany, July 2020-February 2021, aggregate data from the rural area and the city of Osnabrück and Freiburg.
The researchers found 30 studies from Germany and found that the reported seroprevalence was mostly low, below 5%, and mainly from hotspots or group-specific screening. They only considered that a single study, called the Corona substation study of the Rhineland study, fit their criteria. This study calculated a low seroprevalence below 1%, which would mean that Germany remained almost completely vulnerable to the virus.
The current study is based on MuSPAD (Multilocal and Serial Prevalence Study of Antibodies against SARS-2 Coronavirus in Germany) data. MuSPAD is a multi-local study established by researchers to understand the community prevalence of SARS-CoV-2 and allow comparisons with other European countries.
It addresses seroprevalence by region, time points, social and demographic data, and comorbidities. The researchers randomly tested more than 13,000 and 6,000 adults in two rounds of testing in five German counties with Spike S1-specific IgG ELISA (enzyme-linked immunosorbent assay). The first group of participants was tested twice to monitor for changes in seroprevalence over time.
About 40% of participants in both stages had no history of COVID-19-like illness as of February 2020. About 10% had been exposed to a confirmed case.
About 20% had household members who had tested for the virus by PCR. Less than 20% had tested themselves. In the second stage, the proportion was about one-third, in both categories. In one county, Reutlingen, 8% of household members were tested in the first stage, but 45% in the second.
Less than 1% and just over 2% of participants in the first and second stage had tested positive at any time.
Underestimation of infections
Seroprevalence was low until the end of 2020 due to many unreported cases. Seropositivity was almost four times higher among those with two or more COVID-19-like symptoms, such as loss of odor, cough, respiratory distress, fever, or fatigue.
The seroprevalence of the first stage, in June 2020, was 2.4% for Reutlingen; 1.5% for Freiburg; and 2.3% for Aachen. These values increased to 2.9% for Reutlingen in October 2020, stage 2; 2.5% for Freiburg; 5.4% for Aachen; and 1.3% for Osnabrueck, with 2.4% for Magdeburg, both in November-December 2020.
Based on these results, about 2.5-4.5 more cases were reported than reported to health authorities, called the Surveillance Detection Report (SDR). This was the lowest among people aged 80 or older, who had the highest seroprevalence. “Age-specific SDR differences should be considered when modeling and predicting COVID-19 morbidity.“.
With the second wave (November 2020 to February 2021), another 2-5% of the population became infected.
They also found that with efficient insulation and contact tracking, the number of people who needed to be quarantined to prevent an infection was 8.2.
Risks of mortality from infection
Estimates of infection mortality fell between 0.2 and 2.4%, increasing with age.
The odds of seroprevalence were 80% more likely with lower education. In contrast, smoking was related to only half the odds of being HIV-positive. However, there is much evidence to indicate that the disease is much more severe in those with lungs damaged due to smoking,
This is the first population-level seroprevalence study of accurately plotted SARS-CoV-2 in several regions of Germany. The two rounds of sampling helped to monitor seroprevalence variations in these representative regions.
However, seroprevalence could not be measured at all sites simultaneously, meaning that antibody levels would have decreased more significantly in the last ones tested. At the same time, the second wave was established towards the end of the second stage of testing, which is reflected in the test results.
What are the implications?
The five conclusions reached were:
The grouped seroprevalence of 1.3% indicates that the prevalence was underreported, with only 20-40% of cases reported in the first wave, but 40-50% in the second wave.
Seroprevalence remained low until mid-December 2020, in all regions. This was due to the first wave receding in most regions, but for Magdeburg, it represented the appearance of the second wave.
The SDR is twice as high for those aged 80 or over in the first wave and the difference ranges from 25% to 50% for different cities. More efficient detection of older people through notification should help improve predictions and risk assessment models and therefore shape focused preventive interventions.
The low infection mortality rate observed in Magdeburg is attributed to researchers who captured the initial period of the second wave, where the study ended before completing mortality records. For example, they included 15 deaths on November 15, 2020, while at the end of the year there were almost 50.
The study also shows that contact tracking was highly efficient, with only eight people needing to be quarantined to prevent infection.
Finally, the risk of limited education for viral containment was also observed, probably because it is associated with lower socioeconomic status and changes in employment, which raise barriers to personal isolation at home.
“We recommend that prediction efforts use age-specific regional underreporting ratios if they are available to predict more seriously serious courses of illness and death. We also recommend that testing and screening efforts be targeted especially at those younger, middle-aged adult groups that appear prone to the lowest notification in our study.“.
* Important news
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.