ABSTRACT
Since the beginning of the pandemic of COVID-19, there has been a widespread assumption that most infected persons are asymptomatic. A frequently-cited early study from China suggested that 86% of all infections were undocumented, which was used as indirect evidence that patients were asymptomatic. Using data from the most recent wave of the EPICOVID19 study, a nationwide household-based survey including 133 cities from all states of Brazil, we estimated the proportion of people with and without antibodies for SARS-CoV-2 who were asymptomatic, which symptoms were most frequently reported, the number of symptoms reported and the association between symptomatology and socio-demographic characteristics. We were able to test 33,205 subjects using a rapid antibody test that was previously validated. Information on symptoms was collected before participants received the test result. Out of 849 (2.7%) participants who tested positive for SARS-CoV-2 antibodies, only 12.1% (95%CI 10.1-14.5) reported no symptoms since the start of the pandemic, compared to 42.2% (95%CI 41.7-42.8) among those who tested negative. The largest difference between the two groups was observed for changes in smell or taste (56.5% versus 9.1%, a 6.2-fold difference). Symptoms change in smell or taste, fever and myalgia were most likely to predict positive test results as suggested by recursive partitioning tree analysis. Among individuals without any of these three symptoms (74.2% of the sample), only 0.8% tested positive, compared to 18.3% of those with both fever and changes in smell or taste. Most subjects with antibodies against SARS-CoV-2 in Brazil are symptomatic, even though most present only mild symptoms.
ABSTRACT
Population based data on COVID-19 are essential for guiding public policies. We report on the first of a series of planned seroprevalence surveys relying upon on household probabilistic samples of 133 large sentinel cities in Brazil, including 25,025 participants from all 26 states and the Federal District. Seroprevalence of antibodies to SARS-CoV-2, assessed using a lateral flow rapid test, varied markedly across the countrys cities and regions, from below 1% in most cities in the South and Center-West regions to up to 25% in the city of Breves in the Amazon (North) region. Eleven of the 15 cities with the highest seroprevalence were located in the North, including the six cities with highest prevalence which were located along a 2,000 km stretch of the Amazon river. Overall seroprevalence for the 90 cities with sample size of 200 or greater was 1.4% (95% CI 1.3-1.6). Extrapolating this figure to the population of these cities, which represent 25% of the countrys population, led to an estimate of 760,000 cases, as compared to the 104,782 cases reported in official statistics. Seroprevalence did not vary significantly between infancy and age 79 years, but fell by approximately two-thirds after age 80 years. Prevalence was highest among indigenous people (3.7%) and lowest among whites (0.6%), a difference which was maintained when analyses were restricted to the North region, where most indigenous people live. Our results suggest that pandemic is highly heterogenous, with rapid escalation in Brazils North and Northeast, and slow progression in the South and Center-West regions.
ABSTRACT
BackgroundWhile the recommended laboratory diagnosis of COVID-19 is a molecular based assay, population-based studies to determine the prevalence of COVID-19 usually use serological assays. ObjectiveTo evaluate the sensitivity and specificity of a rapid diagnostic test for COVID-19 compared to quantitative reverse transcription polymerase chain reaction (qRT-PCR). MethodsWe evaluated the sensitivity using a panel of finger prick blood samples from participants >18 years of age that had been tested for COVID-19 by qRT-PCR. For assessing specificity, we used serum samples from the 1982 Pelotas (Brazil) Birth Cohort participants collected in 2012 with no exposure to SARS-CoV-2. ResultsThe sensitivity of the test was 77.1% (95% CI 66.6 - 85.6), based upon 83 subjects who had tested positive for qRT-PCR at least 10 days before the rapid diagnostic test (RDT). Based upon 100 sera samples, specificity was 98.0% (95% CI 92.9 - 99.8). There was substantial agreement (Kappa score 0.76) between the qRT-PCR results and the RDT. InterpretationThe validation results are well in line with previous assessments of the test, and confirm that it is sufficiently precise for epidemiological studies aimed at monitoring levels and trends of the COVID-19 pandemic.
