An official from the Centers for Disease Control and Prevention (CDC) said the agency has begun conducting blood tests to determine the exact number of Americans infected with the coronavirus.

On Friday, Joe Bresee, the deputy incident manager for the CDC’s pandemic response, said the agency launched preliminary studies to determine if a person has been exposed to coronavirus, even without showing symptoms, in order to identify cases that may have slipped through the detection process.

Researchers will be conducting serological tests, also known as serosurveys, by analyzing blood samples to find out if a person has developed certain antibodies to the virus, showing that they were previously infected by the virus and have recovered. The study includes representative blood samples from people, including those from different age groups.

“We’re just starting to do testing and we’ll report out on these very quickly,” Bresee told reporters.

The first part of the study includes the collection of blood samples from people in COVID-19 hotspots who were not diagnosed with coronavirus to determine how widely the virus has circulated. It was also planning to conduct a national survey later on by collecting samples from different parts of the country. The final part of the study includes a survey of special populations with health care workers being a top priority. This is to examine the range of COVID-19 spread within them.

CDC has already begun collecting blood samples from undiagnosed persons in COVID-19 hotspots. The timeline of the study involving health workers was not specified, however, Bresee mentioned that CDC hopes to begin conducting the national survey in the summer.

“We think the serum studies will be very important to understand what the true amount of infection is out in the community,” said Bresee.

Studies have shown that people experience mild infections when they get infected by coronavirus. Data from other COVID-19 infected countries show that about 80% of people tested positive for the virus had mild or moderate symptoms. There have been cases where people have tested positive for the virus even without showing any symptoms.

The CDC study aims to help figure out the possible number of mild and asymptomatic COVID-19 cases so that authorities can plan for future responses to the spread of the virus. For instance, if the study shows that a high percentage of people were likely infected during the first wave of the virus, the response to possible future waves of the virus might be aimed toward providing protection and prioritizing the people with high risk.

The CDC has also been adopting a number of surveillance systems to record the toll of coronavirus pandemic in the United States.

On Friday, the CDC published its first weekly COVID-19 surveillance report. It provides a weekly summary and interpretation of key indicators used to track the coronavirus outbreak in the U.S., including information related to COVID-19 outpatient visits, emergency department visits, hospitalizations, and deaths, as well as laboratory data.

The report mentioned that nearly 76,000 Americans were tested for the infection, with nearly 11,000, or 14.5%, testing positive, in the week. It also mentioned that the percentage of deaths due to pneumonia has increased sharply since the end of February, while influenza deaths increased modestly through early March and declined during the week.

As of Monday, the United States reported 337,637 cases of COVID-19 and the death toll reached 9,647. Meanwhile, a total of 1,275,542 cases were reported worldwide.