key: cord-0928350-udq6vw5r
authors: Soriano, Vicente; Meiriño, Rosa; Corral, Octavio; Guallar, María Pilar
title: SARS-CoV-2 antibodies in adults in Madrid, Spain
date: 2020-06-16
journal: Clin Infect Dis
DOI: 10.1093/cid/ciaa769
sha: d253ecd58e39d5620082b366d447742c0c9bba16
doc_id: 928350
cord_uid: udq6vw5r

nan

M a n u s c r i p t Dear Editor:

We read with interest the report by Huff and Singh [1] , where they highlighted the role of asymptomatic transmissions of SARS-CoV-2. The authors pointed out that "public health strategies relying solely on 'symptom onset' for identification of new cases need urgent reassessment". We want to add that information derived from antibody testing may help to obtain a better picture of the coronavirus spread in a given region.

Madrid has been the region more deeply hit by COVID-19 in Spain, with 65,000 confirmed cases and 9,000 deaths up to May 10 th , eight weeks after the country's lockdown had been implemented on March 14 th [2] . We were interested to known in what extent these figures translated into high rates of antibody detection in the community, additionally unveiling asymptomatic cases and persons with symptoms that could not be tested due to shortage of diagnostic tests at the peak of the epidemic.

We retrospectively analyzed all consecutive asymptomatic adults to whom voluntary testing had been offered at our university clinic In Madrid since the last week of April to the first two weeks of May 2020. Capillary blood was examined using PCL COVID-19 IgG/IgM Rapid Gold (PCL Inc., Seoul, Republic of Korea), which is a rapid diagnostic test based on immunochromatography. Specific antibodies against SARS-CoV-2 are recognized using recombinant antigens for the nucleocapsid and the receptor binding domain of the spike protein. The test has granted EU and FDA approval.

We tested 674 adults belonging to different groups, including university employees and their families, health care workers, social services personnel, and persons living in communities, religious or not. Overall, SARS-CoV-2 IgG antibodies were found in 93 (13.8%). Table 1 records seroprevalence rates in groups according to their living ties, i.e. persons without link, family members, and those living in communities of 10-25 persons. The seroprevalence was significantly greater in the latest group compared to the rest (19.2% vs 10.9%; p=0.003).

We found three independent clusters of COVID-19. One occurred in a flat apartment downtown Madrid where 12 women were living together and acknowledged poor A c c e p t e d M a n u s c r i p t preventive measures. All became infected and ten sick, requiring hospitalization two of them. The second cluster involved ten non-related individuals who met together for 3 hours in a small meeting room. Three of them had just returned from Italy and begun with fever and cough two days after. All became ill on the following days, and one required hospitalization at the intensive care unit. Recent seroprevalence surveys from New York State, Los Angeles and Santa Clara, found SARS-CoV-2 antibody rates of 13.9%, 4.6% and 2.8%, respectively, on early April 2020 [3] .

Information from similar surveys in Europe is limited. In France, infection rates of 4.4% have been estimated nationwide based on data from hospitalizations and deaths, being up to 9.9% in Paris [4] .

We found that roughly 10.9% of adults in Madrid (excluding those living in communities) had SARS-CoV-2 antibodies at the time of lockdown release on May 10 th . Given that the population of the Madrid's region is of 6.6 million, the inferred number of infections would be above 700,000, which is more than 10-fold greater than the official 65,000 confirmed SARS-CoV-2 cases. We encourage to perform similar serosurveys periodically and in other regions, to allow proper comparisons of dynamics at distinct sites and the impact of preventive measures.

Conflicts of interest: none for all authors M a n u s c r i p t 

Asymptomatic transmission during the COVID-19 pandemic and implications for public health strategies

Why such excess of mortality for COVID-19 in Spain?

Seroprevalence of SARS-CoV-2 specific antibodies among adults in

Estimating the burden of SARS-CoV-2 in France

A c c e p t e d M a n u s c r i p t