In conjunction with its research partner, the University of Miami Miller School of Medicine, Miami-Dade County has just completed a second round of its COVID-19 community testing to ascertain the prevalence of infection within the County’s 2.75 million residents. The program differs from several others conducted elsewhere in the US in that it employs random sampling, weighted across the County’s 32 municipal statistical areas.

To date, nearly 1,800 individuals have participated in this program. Four hundred were tested during our pilot phase, where we examined the feasibility of our recruitment strategy and implementation methods. Approximately 700 have participated each week thereafter. This represents 85% of residents who were randomly selected to participate in the initiative; participants voluntarily shared information about their health, and gave two drops of blood to determine whether they had produced antibodies to the novel coronavirus infection. Testing for antibodies helps approximate the prevalence, or amount, of infection within our community at a given time.

While this is not a perfect measure, and all antibody tests for coronavirus have known limitations, we believe that our data sheds new light on what is happening in our community. Prior to this testing effort, our best available information came from public testing sites (which are very restricted in terms of who can get tested, thereby giving a very limited understanding of the virus and its local impact), hospitalization data and the medical examiner reports.

Our data from this week and last tell a very similar story. In both weeks, 6% of participants tested positive for COVID-19 antibodies, which equates to 165,000 Miami-Dade County residents. This figure directly contrasts with testing site data, which indicated that there 10,000 positive cases, suggesting that the actual number of infections is potentially 16.5 times the number of those captured through testing sites and local hospitals alone. Using statistical methods that account for the limitations of the test (sensitivity and specificity), we are 95% certain that the true amount of infection lies between 4.4% and 7.9% of the population, or between 123,000 and 221,000 residents. These results are similar but not identical to other recent, non-randomized testing programs that have been conducted throughout the United States.

Importantly, of the individuals who tested positive for the antibodies each week, more than half had NO symptoms in the seven to fourteen days prior to screening. Quantifying the number of asymptomatic individuals with infection is critically important for public health, as these individuals do not feel sick or unwell, and may unintentionally transmit the virus to others. This is particularly true for vulnerable population groups who may be at increased risk for hospitalization and death from COVID-19.

From national data, we have observed disparities in who is at risk of getting COVID and who dies from it. Our data uphold a similar trend locally. In particular, the data indicates that African American and Caribbean communities may be twice as likely to be infected with COVID-19 than other racial groups. While we cannot fully explain these differences yet, we are committed to trying to address them. We will work with key leaders across the County to determine how to best increase testing opportunity, as well as, support navigation to resources to further reduce exposure and transmissibility of infection.

We will also continue community testing, and begin re-engaging participants who screened positive in week one and/or two to undergo follow up screening. This serial testing may give us novel insight into how long antibodies persist, providing an invaluable tool to help "manage the curve" and get our community safely to work again. We will share our data with the Florida Department of Health and with epidemic modelers at the University of Washington to leverage state and national expertise to improve broader understanding of COVID-19 and inform an ever-evolving public health response.

While 6% represents a substantial infection rate, the fact that this number held steady implies that our physical distancing is working and that together, we are "flattening the curve." That is why any openings we are planning for parks and other places will require strict following of social distancing and police will be out enforcing the rules. We want to get to a "new normal," but we can only do that if people take personal responsibility.