Photo: Mostphotos

During the COVID-19 pandemic, free PCR testing was offered throughout Sweden. However, a new study from the Department of Public Health Sciences at Stockholm University shows that it was far from self-evident who actually got tested – and that differences in testing behavior followed clear social and demographic patterns.

The study, published in the scientific journal European Journal of Epidemiology, is based on 1.5 million working-age individuals in the Swedish regions Stockholm and Skåne who carried out just under 495,000 PCR tests between July and December 2020. By linking test results to national registers, the researchers were able to examine differences in testing behavior based on gender, education, income, country of birth, and health status.

Most likely many undetected cases 

The results show that men, people with low levels of education, and people born outside Europe got tested less frequently than women, people with higher education, and those born in Sweden. When these groups did get tested, their results were more often positive, and they were at significantly higher risk of being hospitalized.

People with higher education and income got tested more often, but their test results were less frequently positive.

Photo: Bildbyrån

“In groups where few people got tested but positivity rates were high, there is reason to believe that there were relatively many undetected cases. We already know that socially disadvantaged groups and people born abroad were particularly hard hit by the pandemic. Our results show that differences in testing behavior may have contributed to this,” says Olof Mpumwire Östergren, researcher at the Department of Public Health Sciences, Stockholm University.

Testing is a social behavior

Testing behavior depended on a number of factors, the researchers note. The marked differences in testing by gender, socioeconomic status, and national background – even after adjusting for occupation, age, and likely exposure in the neighborhood – indicate that testing is a social behavior.

Social norms encouraging individuals to get tested may be especially strong in groups that are also economically and socially well equipped to adapt their lives to a positive test result. Although fear of severe illness may be equally strong across groups, fear of indirect consequences of a positive result – such as having to stay home and lose income – may deter some individuals from testing.

More equitable testing strategies needed

The study further shows that areas with lower testing rates often had more hospitalisations, suggesting that the spread of infection in these areas was underestimated during the acute phase of the pandemic. The results presented in the study show that differences in testing behavior meant that official statistics did not give a representative picture of the infection’s spread, which in turn may have made it harder for policymakers to direct efforts where they were most needed.

The researchers argue that future pandemics require more equitable testing strategies. One proposal is to allocate part of the testing capacity for random and representative testing, as well as to collect data on both positive and negative test results.

“It’s important to balance individuals’ need to test to protect themselves and those around them against society’s need for an accurate picture of where the infection is. This can be achieved with relatively simple measures—for example, by collecting information on negative tests. That would be an important part of preparedness for the next pandemic,” Mpumwire Östergren says.

Håkan Soold