Median age of first patients diagnosed with COVID-19 in Brazil was lower than elsewhere

Study shows that the 20-39 age group accounted for almost half the cases confirmed in the first month, possibly explaining why a smaller proportion of the total number infected were hospitalized in the period.

By Elton Alisson  |  Agência FAPESP – The median age of the patients diagnosed with COVID-19 in the first month of the epidemic in Brazil was 39, less than in other countries.

This factor, in conjunction with the fact that a large proportion of initial patients belonged to higher-income groups, may have contributed to the relatively low hospitalization rate in Brazil in the period, which was only 10%, compared with 20% in the US, for example.

These are some of the findings of an international study led by Brazilian researchers and supported by FAPESP under the aegis of the Brazil-UK Center for Arbovirus Discovery, Diagnosis, Genomics and Epidemiology (CADDE). 

A preliminary report on the study is published on the platform medRxiv in a preprint (not yet peer-reviewed) version.

“These first infected patients were relatively well-off and so were able to get diagnostic testing, for example, facilitating early social isolation and reducing contagion,” Julio Henrique Rosa Croda, one of the authors of the study, told Agência FAPESP. Croda is a researcher at Fundação Oswaldo Cruz (Fiocruz), one of Brazil’s main biomedical and public health research centers.

The researchers analyzed the epidemiological, demographic and clinical characteristics of COVID-19 cases confirmed between February 25 and March 25, 2020.

Their main data source was the REDCap notification database established at the start of the outbreak by the Brazilian health ministry.

Their analysis of the data showed that 1,468 cases of COVID-19 were confirmed in Brazil in the period, 48% of these patients were aged 20-39, and 10% were hospitalized. Cardiovascular disease and high blood pressure were associated with hospitalization.

“The median age of hospitalized COVID-19 patients in Brazil may be lower than elsewhere because of a higher prevalence of co-morbidities than among people in the same age group in other countries, but this hypothesis is yet to be confirmed,” Croda said. 

Another possible explanation for the lower age of hospitalized patients with the disease in Brazil is that the 20-39 age group corresponds to a sizable proportion of the total population (32%), he said.

Class differences

To find out whether the first notified cases of infection by SARS-CoV-2 were associated with income and socio-economic status, the researchers looked for correlations with the patients’ residential addresses in metropolitan São Paulo.

The analysis showed that the proportion of tested cases rose as neighborhood per capita income increased.

“We detected a socio-economic disparity in access to COVID-19 diagnostic testing in Brazil. This inequality has persisted as the number of cases has grown,” Croda said.

The researchers also found that only 33.1% of cases were confirmed by public laboratories during the first month of the epidemic. The rest were confirmed by private laboratories.

“The disease was initially confined to the well-off. In late March there was a transition and it spread to lower-income groups,” Croda said.

The article “Epidemiological and clinical characteristics of the early phase of the COVID-19 epidemic in Brazil” (doi: 10.1101/2020.04.25.20077396) by Julio Croda, Ester C. Sabino, Nuno Rodrigues Faria et al. can be read at: www.medrxiv.org/content/10.1101/2020.04.25.20077396v1.full.pdf.