Community seroprevalence of COVID-19 in probable and possible cases at primary health care centres in Spain

Fam Pract. 2021 Mar 29;38(2):154-159. doi: 10.1093/fampra/cmaa096.


Background: There is a scarcity of information about patients with mild or moderate symptoms during the coronavirus disease 2019 (COVID-19). This is especially true for those who attended and were followed up at primary care settings.

Objectives: We aim to measure the seroprevalence of antibodies against SARS-CoV-2 infection in a community sample of possible cases and among probable cases followed in primary care.

Methods: We selected a random sample of 600 individuals stratified by age groups from a total population of 19 899 individuals from a community area in Barcelona. We also invited all the patients that had been followed by General Practitioners (GPs). For both populations, we used COVID-19 rapid lateral flow immunoassays, which qualitatively assess the presence of patient-generated Immunoglobulins G (IgG) and Immunoglobulin M (IgM).

Results: Three hundred and eleven asymptomatic individuals from the randomly selected sample participated in the study. The mean age was 43.7 years [standard deviation (SD) = 21.79] and 55% were women. Seventeen individuals were seropositive for IgM and/or IgG, resulting in an overall prevalence of 5.47% (95% confidence interval = 3.44-8.58). Six hundred and thirty-four symptomatic patients were followed up by GPs. The mean age was 46.97 years (SD = 20.05) and 57.73% were women. Of these, 244 patients (38.49%) were seropositive. Results of the multivariate logistic regression analysis showed that the odds ratio for a positive test was significantly increased in patients who had fever, ageusia and contact with a patient diagnosed with COVID-19.

Conclusions: The seroprevalence of antibodies against SARS-CoV-2 among possible cases was lower than expected. Approximately, 40% of the symptomatic patients followed up by GPs during the peak months of the pandemic were positive.

Keywords: General practice; infectious diseases; practice management; primary care; public health; screening.

Publication types

  • Observational Study

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • COVID-19 / diagnosis*
  • COVID-19 / epidemiology*
  • COVID-19 Serological Testing*
  • Child
  • Child, Preschool
  • Cross-Sectional Studies
  • Female
  • Follow-Up Studies
  • Humans
  • Infant
  • Logistic Models
  • Male
  • Middle Aged
  • Prevalence
  • Primary Health Care*
  • Prospective Studies
  • Seroepidemiologic Studies
  • Severity of Illness Index
  • Spain / epidemiology
  • Young Adult