Cascais Municipality SARS-CoV-2 survey: 1st phase results

Having as a mission «To foster research, training and implementation on Global Health and Tropical Medicine», GHTM R&D Centre’s researchers are very interested to better understand the percentage of SARS-CoV-2 infections in the Portuguese Speaking Communities, in Portugal or abroad.

In May 2020, the Cascais City Council established a partnership with GHTM to conduct a community-level seroprevalence survey, which included blood serology testing for SARS-CoV-2 antibodies together with socio-demographic and clinical questions.

The survey’s general goals were:

to estimate Cascais municipality SARS-Cov-2’s seroprevalence;
to identify associated socio-demographic and clinical factors .

This 1^st phase of the study comprehended the pandemic period between May and September 2020, and had 12,032 respondents, corresponding to 5.62% of Cascais’ total population.

The lab assay used to detect SARS-Cov-2 IgG/IgM antibodies was the ROCHE SARS-CoV-2 Rapid Antibody Test.

The percentage of reactive tests was 1.3% (95% C.I.: 1.12 – 1.53) overall, 1.16 % among females and 1.56 % of males. The age group with the highest prevalence (2%) was 20-39 years old. Generally, there were not significant differences among educational levels or professional status. However, immigrant respondents had a significantly higher seroprevalence (2.99% vs 1.31%) p<0.05. Moreover, immigrants in the age group of 20-29 years old had significantly a higher seroprevalence when compared to the others (11.1%).

Furthermore, a significantly lower seroprevalence was found among patients reporting to have Diabetes (0,58%) and cardiovascular disease (0,76%), possibly reflecting higher levels of adherence to social distancing recommendations in these patients, for which a high risk for severe disease was reported since the beginning of the pandemic.

The sample comprised 1669 people who had done at least a PCR test, with 60 positives. Of these, unexpectedly, 32.8% did not test positive for IgG/IgM antibodies. Among the 5.3% of respondents who reported contact with a suspected or infected person, 9.65% were reactive.

Of the 44.3% of respondents that mentioned having had one symptom congruent with COVID-19, 2.02% were serum-positive. 1.8% of these never did a PCR test and were seropositive. On the other hand, of the 158 serologic reactive, 31.6% were asymptomatic. The most frequent symptom of the disease was fatigue, referred by 37.4% of the reactive, although loss of taste or smell are the most specific COVID-19 symptoms, as 98.6% and 98.3%, respectively, of seronegative people did not show them.

These results highlight represent the largest serological SARS-Cov-2 survey in Portugal. Questionnaires are still being analysed and further results, corresponding to the time period between October 2020 and January 2021 will be reported soon.