As public health experts plead for cities and states to dramatically increase the scale and speed of testing and contact tracing for the coronavirus, researchers in San Francisco, backed by dozens of volunteers, have launched an ambitious effort to test everyone older than 4 years old in a big part of one hard-hit neighborhood. They're calling the effort "Unidos en Salud – United in Health."

Epidemiologists and others at the University of California, San Francisco are trying to determine how deeply the virus has penetrated this one, densely populated section of San Francisco's Mission District, a gentrifying but still predominantly Latino neighborhood.

"Right now, all of our information is really coming from people who are sick," says Dr. Gabriel Chamie, a professor of infectious disease and medicine at UCSF, who is helping to lead the testing study. "That's sort of the tip of the iceberg. We know that. To what extent or what size that iceberg is, outside of the hospital, needs to be determined. The purpose of this study is to understand the value of expanding testing to people without symptoms" in the surrounding area.

The goal is to test everyone over age 4 who lives in the census tract — more than 5,700 residents — simultaneously for both an active infection (using PCR tests, via nasal and throat swab) and for recent past exposure to the virus (using antibody tests, via a finger-prick blood sample). That sort of double-testing of each person provides important information not only about active infections in the neighborhood right now, but also about the number of people who have been exposed in the past and may or may not have developed symptoms.

California still has only tested a little over 1% of the state's population.

Gov. Gavin Newsom has repeatedly pledged to ramp up testing and contact tracing where testing has been limited or non-existent. That includes some rural areas of the state, as well as some communities that are largely African-American and Latino — groups that have been particularly hard-hit by the coronavirus in the U.S.

And the state recently became the first in the nation, according to Newsom's office, to recommend that all asymptomatic people in certain high-risk settings — such as residents and staff in nursing homes and in prisons — get tested for the virus.

These tests go further.

"What we're doing here, essentially, in this small census tract is what the country needs to be able to do to open back up," says Jon Jacobo, who is with the Covid19 Latino Task Force, which mobilized volunteers, nonprofits and Latino community groups to help with the testing project.

"We need to be able to do the testing, the isolation, the follow up, the contact tracing. And until we can do that," he says, "things are not going to go back to normal."

The testing for this project, which began last Saturday in several schools and parks, is scheduled to run through the end of the day Tuesday, with some follow-up, as needed, for people unable to leave their homes.

The Mission District, an area surrounding San Francisco's 18^th century Mission Dolores, is the part of San Francisco hardest hit by the virus, so far, mirroring the growing income inequality and health care disparities in the city. Latinos are 15 percent of San Francisco's population but make up more than 25 percent of all confirmed COVID-19 cases, according to data from the county's department of public health.

The county health director, Dr. Grant Colfax, on Monday said San Francisco needs two- to three-times more testing than current levels before relaxing public health stay-at-home orders and other social distancing measures.

Few U.S. cities have tried to test nearly everyone. Rural Telluride, Colo., is one town that gave a majority of its residents antibody tests, in hopes of determining what percentage of people had a history of infection with the virus. The effort's usefulness to Telluride was blunted, however, by an unforeseen three-week delay in getting test results back.

"OK, we all need to social distance" a volunteer in San Francisco told people Monday, in a long line that stretched around the Mission's Garfield Square. Nurses, doctors and volunteers in protective gear hurried around white pop-up tents on a field that in the days before the coronavirus would have been filled with soccer games and kids.

"Any symptoms like fever? Any dry coughing?" asked medical student Fabian Fernandez, as he also tried to put people at ease while they waited for the nasal swab and finger-prick blood sample of each test.

"I mean some people [are] joking, like 'is this gonna be like a microchip you're implanting?' " Fernandez said of the nasal swab, and chuckles. "But I think, for the most part, people understand that what we're doing here is really important to understand the demographics of this virus."

UCSF researchers hope to have the results of the PCR tests within 72 hours. The antibody test results, however, will take three to four weeks. In light of the pandemic, the study is being fast-tracked, UCSF researchers say, and they hope to publish their results by the end of May.

The tests are free to the public — paid for by UCSF in partnership with the Chan-Zuckerberg Biohub and a separate philanthropic initiative that helped expand UCSF's capacity to process coronavirus tests.

Turnout has been good so far, the UCSF researchers say. By the end of the day Monday, more than 2,500 residents had been tested. To get people to show up, a small army of volunteers for the project hit the streets starting Saturday, knocking on doors and passing out flyers in English and Spanish — offering information about the project going on at testing sites set up around the neighborhood.

That caught the attention of locals including Norma Garcia. "I think it's good for me to know, to take precautions — to protect other people, my neighbors, my community," she says.

Wearing protective masks as they waited in line for a test Monday, Mission residents Jeanette Gehrig and Ian Schillebeeckx, both trained scientists, said they jumped at the chance to get tested when they saw the flyer about it.

"Most people being tested have symptoms. So the positive rate is artificially high," Gehrig said. "So I think just getting a better sense of how many people in this area actually have it or have had it — it'll be useful."

People who test positive will get follow up "contact tracing" phone calls and texts from UCSF experts who, as NPR's reported, are working with the city's health department and the Latino Task Force. They will be asked to self-quarantine for two weeks.

Jacobo with the Latino Covid19 Task Force, who lives in the neighborhood, says that's been an obstacle to testing for some in the community. They might be the family's sole income earner, he says, and fear the 14-day quarantine and the loss of income if they test positive — they don't want to know if they have the virus.

"Maybe you're undocumented and can't miss work and don't get federal stimulus checks. So there's just this whole complication of some of the fears and the angst and the anxiety. And so we're trying our best to work through that and message the fact that, 'look, at its core this can be life or death,' " Jacobo says.

Jonathan Marquez got the message. He was in line with two relatives. The 19-year-old said they wanted to get tested for peace of mind and to help keep themselves and co-workers safe. Some people in his community, he noted, are working two or three jobs to get by financially — often in front-line delivery and cleaning work.

"An example [in] my family — two of my family members work cleaning houses," Marquez said. "So it's like not only for them, but the people they work with. Get tested, be a little more safe – and, hopefully, get back to work as soon as possible."

The 19-year-old college student also works at the San Francisco Giants' Oracle Park during baseball season. Marquez said he wants to know as much as he can before school and baseball return.

Marquez just doesn't know when that'll be.

Copyright 2021 NPR. To see more, visit https://www.npr.org.