Prevalence Of COVID-19 Antibodies In Washoe Co. Expected To Be Low

Jun 22, 2020

Coverage of novel coronavirus is supported by the Mick Hitchcock, Ph.D., Project for Visualizing Science, a science reporting project from the Reynolds School of Journalism.

The Washoe County Health District is conducting its first antibody study to learn the prevalence of COVID-19 in the general population. This requires a blood test that looks for antibodies, which are the body’s immune response to a past infection.

The Nevada State Public Health Laboratory worked on validating the antibody test before it was used in the study.

As KUNR’s Anh Gray reports, getting a representative sample of the county for the study is a complex process.


To determine the prevalence or percentage of people in Washoe who might have been infected with COVID-19, an antibody study is needed on a sample size that can be representative of the general population, so in late May, Washoe’s health district mailed more than 1,000 invitations to randomly-selected households.

The study was designed using the Centers for Disease Control and Prevention Community Assessment for Public Health Response (CASPER) toolkit, which provides epidemiologic techniques for sampling methodology and study assessements.

Epidemiology Program Manager Heather Kerwin is with the Washoe County Health District. She says as part of the study, a survey with questions related to health and demographics was also administered in English and Spanish.

“We weight population, demographic factors against our survey participants,” Kerwin said, “to make sure that we're accounting for disparate participation by age, by gender, by race, ethnicity. We'll even try [to] pull in income, if we can.”

Letters were sent throughout the county, but snail mail proved to be a challenge.

“It has been taking a little bit longer for mail delivery,” Kerwin explained. “People were not going to and from work, and so sometimes people were not in their normal habit and pattern of checking their mail regularly.”

The county is divided into 173 census blocks, and about seven households from many blocks were randomly selected to receive an invitation. Then one adult per household could choose to get the serology test, which detects antibodies in the blood.

But responses were not flooding in after the mailed letters were sent. Kerwin says there weren't responses from 45 census blocks, so to drum up more participants, health officials followed up.

“Teams went out and knocked on over 250 household doors, reminding them that they had received a letter," Kerwin explained. “And in some instances we found, these are addresses that nobody could deliver to, and [due to] some other barriers that we found in the field, they hadn't even received some of the letters.”

The initial goal of the study was to get about 500 people, but they only got 233. Health officials learned a few factors may have contributed to fewer participants. More than 100 letters were returned and marked “undeliverable.” Some people had scheduling conflicts during designated testing days, and Kerwin says some may not have been interested because of growing complacency about the pandemic.

Dr. Wei Yang is a professor with the Division of Epidemiology, Biostatistics, and Environmental Health with the University of Nevada, Reno School of Community Health Sciences. He helped with the study design. He says researchers can still gain more insights about how widespread COVID-19 is in the community from this initial study.

“But this is just a part of the understanding,” Yang explained. “As I mentioned, we cannot emphasize too much of a significance because this is just the start.”

"In studies, generally a larger sample size would yield more precise data, but to be clear, without having completed data analysis yet," Yang said, “I couldn't make conclusions of the margin of error at this point.” 

The health district plans to eventually reproduce the study two more times. The second study would likely take place in the fall before the start of the cold and flu season. The third study, will likely be sometime in the spring of next year. The goal is to understand the spread of COVID-19 over time.

So far, scientists have not yet concluded whether having antibodies can actually protect against future infections, but for some, having information about past exposure can be useful.

Adam Mayberry is the communications manager for the Truckee Meadows Fire Protection District (TMFPD). He says the agency administered an FDA-approved antibody test to 132 personnel in May.

“A majority of them are what we consider our frontline staff,” Mayberry said, “our firefighters, paramedics, captains, battalion chiefs, those that are in residency on a daily basis fighting fires, responding to rescue incidents.”

Fourteen percent of tests came back positive for antibodies, but the particular test available to them at the time could detect four types of coronaviruses, and COVID-19 was one of them. Even though it wasn’t definitive, Mayberry said, “We just felt a real important desire to better understand how the COVID-19 pandemic was affecting our staff, given that we’re first responders. It really allowed us to have a better understanding, a general understanding, if in fact they were protected against a coronavirus.”

About 85 percent of calls for help to the agency are medical-related, according to Mayberry. He says more antibody testing later on could be used to compare and understand personnel exposure to COVID-19 over the course of the pandemic since the agency now has some baseline data. Also, TMFPD is now offering employees, who want to get an antibody test that's specific to detecting COVID-19, the option to get one through a private lab.

As for prevalence in the general population, Washoe’s health district plans to release findings once they become available. The data will provide a more accurate picture of how widespread the virus is in the county, more insights on the fatality rate, and how much of the population might have some immunity. For now, researchers estimate only a small percentage of Washoe residents have antibodies; the rate is expected to be in the single-digit range.