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Volume 27, Number 11—November 2021
Dispatch

Prevalence of SARS-CoV-2 Antibodies after First 6 Months of COVID-19 Pandemic, Portugal

Luísa Canto e Castro, Ana Helena Guia Pereira, Rita Ribeiro, Catarina Alves, Luís Veloso, Vera Vicente, Dalila Alves, Inês Domingues, Cláudia Silva, Andreia Gomes, Marta Serrano, Ângela Afonso, Marc Veldhoen, Maria José Rego de Sousa, José Germano Rego de Sousa, Germano de Sousa, Maria M. Mota, Bruno Silva-Santos1, and Ruy M. Ribeiro1Comments to Author 
Author affiliations: Fundação Francisco Manuel dos Santos, Lisbon, Portugal (L. Canto e Castro); Universidade de Lisboa, Lisbon (L. Canto e Castro, I. Domingues, C. Silva, A. Gomes, M. Serrano, Â. Afonso, M. Veldhoen, M.M. Mota, B. Silva-Santos, R.M. Ribeiro); Centro de Medicina Laboratorial Germano de Sousa, Lisbon (A.H.G. Pereira, R. Ribeiro, M.J. Rego de Sousa, J.G. Rego de Sousa, G. de Sousa); CTI Clinical Trial and Consulting Services, Portugal (C. Alves, L. Veloso, V. Vicente, D. Alves); Los Alamos National Laboratory, Los Alamos, New Mexico, USA (R.M. Ribeiro)

Main Article

Table 2

Prevalence of antibodies against severe acute respiratory syndrome coronavirus 2, weighted and adjusted for the strata, by sociodemographic, health, and epidemiologic characteristics, Portugal, September 8‒October 14, 2020*

Characteristic No. participants Seroprevalence, % (95% CI)
Overall
 13,398
 2.2 (2.0–2.5)
Sex
M 5,985 2.3 (2.0–2.8)
F
 7,413
 2.1 (1.9–2.6)
Persons per household
1 1,141 2.1 (1.6–4.6)
2‒4 11,139 2.1 (1.9–2.5)
>5
 1,069
 2.3 (1.9–4.5)
Education
Less than high school 4,145 2.1 (1.7–2.8)
High school, post-high school, no undergraduate degree 3,373 2.0 (1.8–3.1)
Undergraduate or graduate degree 5,603 2.1 (1.8–2.7)
Other
 270
 2.9 (2.1–10.6)
Occupation
Employed 7,584 2.3 (2.0–2.8)
Unemployed 668 2.5 (1.9–5.1)
Student 2,488 2.3 (1.9–3.5)
Retired 1,943 1.6 (1.2–3.0)
Disability 143 0.3 (0.2–3.0)
House worker 223 1.0 (0.5–6.6)
Other
 333
 3.8 (2.9–9.1)
Professional sector
Commerce/industry/building 1,324 2.7 (2.2–4.3)
Administration/services 1,930 2.5 (2.0–3.7)
Education 1,351 1.5 (1.1–3.1)
Health 875 3.2 (2.4–5.9)
Transportation 207 3.2 (2.3–10.3)
Other
 1,772
 1.8 (1.4–3.0)
For employed workers, current working arrangements
Teleworking
No 6,480 2.4 (2.2–3.0)
Yes 1,104 1.4 (1.0–3.1)
Physically at work, contact with colleagues
No 263 2.8 (2.0–8.4)
Yes 6,579 2.3 (2.1–2.9)
Physically at work, contact with the public
No 4,184 2.3 (1.9–3.0)
Yes
 3,400
 2.3 (2.0–3.2)
Body mass index, kg/m2†
Underweight and normal weight, <24.99 5,352 1.8 (1.5–2.3)
Overweight, 25.00–29.99 4,166 2.4 (2.0–3.1)
Obese, >30.00
 1,766
 2.5 (2.0–3.7)
Smoking status
Non-smoker 9,235 2.4 (2.1–2.9)
Ex-smoker 2,298 2.2 (1.8–3.4)
Smoker 1,862 1.0 (0.9–2.2)
<20 cigarettes/day 1,689 1.1 (0.9–2.4)
>20 cigarettes/day
 173
 0.0 (0.0–5.2)
Physical exercise
No 7,590 2.2 (2.0–2.7)
Yes
 5,808
 2.0 (1.7–2.5)
BCG vaccine
No 688 2.6 (2.0–5.2)
Yes 10,672 2.2 (2.0–2.6)
Do not know
 2,038
 2.0 (1.6–3.2)
Chronic disease
No 9,681 2.2 (2.0–2.6)
Yes
 3,717
 2.0 (1.6–2.8)
Were you in contact with someone infected?
No 3,621 0.7 (0.6–1.3)
Yes 1,025 16.2 (14.2–19.3)
Do not know
 8,752
 1.2 (1.1–1.6)
Where was this potential contact?
Household 295 23.6 (19.8–30.3)
Work 432 9.6 (7.7–17.2)
Family outside household 210 12.9 (10.2–20.9)
Healthcare institution 48 7.5 (5.2–20.9)
Do not know
 40
 18.4 (13.8–35.7)
Was someone in your household given a diagnosis of COVID-19?
No 12,997 1.3 (1.2–1.6)
Yes
 401
 28.3 (24.5–33.7)
Were you given a diagnosis of suspected COVID-19?
No 12,729 1.1 (1.0–1.4)
Yes
 669
 22.7 (19.9–26.8)
If you took a SARS-CoV-2 test, what was the result?
Positive 136 80.1 (70.4–82.3)
Negative 2,030 2.5 (2.1–4.0)
Inconclusive
 27
 22.4 (15.4–37.1)
If you took an antibody test before, what was the result?
Positive 31 62.1 (45.7–69.2)
Negative 219 1.9 (1.4–11.1)
Inconclusive 9 8.0 (4.6–18.8)

*We include the number of participants in the study for reference purposes; these numbers are not adjusted for the population. BCG, Bacillus Calmette–Guérin; COVID-19, coronavirus disease; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2. †Calculated only for adults (>18 years of age).

Main Article

1These authors were co-senior authors.

Page created: August 10, 2021
Page updated: October 19, 2021
Page reviewed: October 19, 2021
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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