The number of Houstonians who had COVID-19 could be four times higher than indicated by viral testing, according to new data from the Houston Health Department. The department tested the blood of volunteers from randomly selected Houston households for the presence of COVID-19 antibodies, an indication of previous infection.

Data from the antibody testing survey, an ongoing collaboration between the health department, Baylor College of Medicine and Rice University, shows an estimated 13.5% of Houstonians (approximately 250,000 people) previously had COVID-19 by September 19. At that time only 57,000 infections were identified by traditional viral testing.

“Transparency is a critical part of our mission during the pandemic and our goal is to keep the public informed about the COVID-19 infection rate and how people can practice safe and healthy habits,” said Mayor Sylvester Turner. “This information, combined with findings from the department’s wastewater testing, PCR clinical case surveillance system and other programs, analyzed with advanced data science techniques, gives us invaluable insight to precisely target testing and educational resources to help save lives.”

The results showed that a higher proportion of people with COVID-19 antibodies lived in high positivity rate areas (18%) of the city than those who lived in low positivity rate areas (10%).  In addition, more women (17%) than men (10%) had antibodies, more Hispanics (18%) and Blacks (15%) had antibodies than non-Hispanic Whites (5%), and more people under 40 years of age (17%) than 40 and older (9%) had COVID-19 antibodies in their blood.

“The statistically designed study produces scientifically sound estimates of the prevalence of SARS-CoV-2 virus in our community,” said Dr. Katherine B. Ensor, Noah G. Harding Professor of Statistics at Rice University and incoming president-elect of the American Statistical Association.

“Along with tracking virus spread, the survey will provide insight on how much antibodies were made and how long they last over a 4-month interval (short-term duration) in blood circulation. In addition, the survey may help identify short-term immunity after infection,” said Dr. Pedro Piedra, professor of molecular virology and microbiology at Baylor College of Medicine.

“We used two labs to verify results and we are confident this data gives us reliable new information on the extent of the spread of this virus in our community,” said Dr. Loren Hopkins, chief environmental science officer for the Houston Health Department.

The survey was conducted September 8-19 when teams from the health department and Houston Fire Department visited 420 randomly selected Houston households where 678 people voluntarily gave a blood sample.

“This antibody testing investigation is a wonderful example of a partnership between academics and a local health department to answer key questions together about a pandemic that is poorly understood,” said Dr. Elaine Symanski professor in the Center for Precision Environmental Health and Department of Medicine at Baylor College of Medicine. “It would not have been possible without the critical involvement of Houstonians who agreed to participate. We owe them a great deal of thanks.”

Survey teams will conduct phase two of the survey in January when people who participated in phase one will be re-tested to measure the number of antibodies remaining in their blood. Teams will also visit 420 new random Houston homes to ask for voluntary blood samples.

Only homes approached by the teams are eligible to participate, and participation is voluntary. The teams will be identifiable by their “Better. Together.” shirts.

This survey is funded by the Centers for Disease Control and Prevention.

For more information, visit HoustonEmergency.org (https://houstonemergency.org/covid-19-antibody-testing-survey/) .