A new Moffitt Cancer Center study shows that the number of Hillsborough County (Tampa area), residents who’ve been infected with COVID-19 is twofold the number of positive tests reported by the Florida Department of Health.
U.S. public health data shows the number of people who test positive for COVID, rates of hospitalization and deaths, but does not accurately reflect the actual extent of the pandemic. Why? These data do not take into account people who were symptomatic but did not undergo testing, and those with mild or no symptoms who were not tested. Early on in the pandemic, testing availability and eligibility requirements also changed.
In a new article published in the March issue of Emerging Infectious Diseases, a journal of the Centers for Disease Control and Prevention, Moffitt researchers set out to estimate the percentage of Hillsborough County residents who had COVID infection and better understand demographics and behavioral factors associated with infection.
COVID-19 antibodies can be detected seven days after symptoms begin and IgG antibodies are detectable within two weeks of infection. Antibody testing is an accurate marker of previous COVID infection regardless of whether symptoms were experienced.
As of June 1, 2021, Florida had the third highest number of confirmed COVID cases in the United States: 2,283,315 (10.6% of residents), resulting in 95,210 hospitalizations and 36,869 deaths. As of June 1, 2021, Hillsborough County had 142,013 positive tests out of approximately 1.47 million residents, or 9.7% of the population.
Moffitt researchers conducted a study of adults in Hillsborough County from October 2020-March 2021. Forty-thousand letters or postcards and 10,000 emails were sent to residents, resulting in a sample size of 867. Participants were scheduled for an in-person blood draw — excluding anyone experiencing symptoms — after completing a short questionnaire on demographics, COVID exposure history, underlying conditions, immunosuppression status and use of immunosuppressive medications.
Among 867 Hillsborough County residents who had not received a COVID vaccine, 19.5% tested antibody positive. This is twofold higher than the confirmed COVID infections reported by the Florida Department of Health for that period of time. Given molecular testing was not widely available early in the pandemic, and when it was available, not everyone experiencing symptoms sought testing, many who were infected were not counted in public health databases.
“A key finding of this study is that nearly 100% of persons who had confirmed or suspected infection were antibody-positive and remained antibody-positive even if the infection occurred more than six months before antibody testing,” said Dr. Anna Giuliano, the founding director of the Center for Immunization and Infection Research in Cancer at Moffitt. “A question that remains unanswered by our analysis and other studies is the duration of the antibody response among those who experienced infection with COVID-19.”
Other key findings include:
- Mask wearing was not associated with antibody status. Nearly 100% of respondents reported mask usage.
- Social-distancing behaviors consistently emerged as a factor associated with risk for infection, with 11% of participants reporting that they never, rarely, or almost never practiced social distancing. This included not avoiding crowds and interacting with a known or suspected virus-positive family member, co-worker or friend
- The percentage seropositive increased with increasing hours per week exposed to an infected person.
- Participants with autoimmune disease or on immunosuppressant medication had lower rates of antibody positivity, roughly half that of the overall study population. This finding is likely attributable to extra precautions taken to avoid infection as opposed to a reflection of actual susceptibility to illness.
- The odds of a positive antibody test was highest among those with a family member as a known virus-positive contact. In shared family spaces where social distancing may not be possible, risk for household transmission is high. Asymptomatic transmission before the onset of symptoms in a household is also highly probable.
- Essential workers, including those working in grocery stores, had higher odds of antibody positivity.
- About 8% of antibody-positive people never had COVID-19 symptoms.