Focus falls on clusters of large virus outbreaks

Expert says officials need to target hot spots, which seem to be big gatherings

After two-and-a-half months of lockdown restrictions to slow the spread of COVID-19, it’s become clear where Californians are most at risk. Long-term care homes for the elderly, jails and prisons, food processing plants and social gatherings appear to be the main culprits for repeated outbreaks. And as communities begin lifting restrictions on churches, schools and other large gatherings, the state’s major outbreaks offer clues to where health measures are most needed going forward. “We’re clearly seeing those clusters of cases occurring in these congregate settings — that is a warning to us that in those types of settings we have to be

more vigilant,” said Dr. Lee W. Riley, a professor of infectious diseases and vaccinology at the UC Berkeley school of public health. A Bay Area News Group review of known major outbreak clusters across California shows they account for a significant share of the state’s more than 100,000 cases: • An outbreak of more than 1,100 infections among inmates and staff at a federal prison complex in Santa Barbara County is among the biggest concentrations of cases in the country. • The nearly 17,000 residents and workers infected in California’s skilled-nursing and residential care facilities for the elderly make up more than 16% of the state’s total COVID-19 cases. • The more than 2,000 who have died at those facilities make up more than half the state’s coronavirus deaths. And the list of major outbreaks continues to mount: 693 infected at a state prison in Chino, 355 at a Los Angeles jail, 188 at a Visalia nursing home, 180 infected at Central Valley Meat Co. in Hanford, 103 aboard a cruise ship that anchored in Oakland, 71 at a Sacramento church and 106 at a San Francisco homeless shelter. Smaller case clusters locally in the past week include 39 infected at Morgan Hill seafood wholesaler Lusamerica Fish, 12 at a Cardenas Markets store in Oakland, and four family gatherings in Santa Cruz County, including a Mother’s Day celebration, that together boosted the county’s case total 20%. What makes places like these hot spots? Riley said a lot has to do with the nature of the coronavirus. The infected tend to “shed” the virus for up to five days before they start feeling ill, he said, much longer than the day or two with influenza. That means people are going to work and socializing without knowing they are transmitting the virus. Even so, he said it takes about 15 minutes of close contact for the “viral load” to reach a threshold that causes a nearby person to catch the disease. “You really need close contact for a period of time for this to happen,” Riley said. “The number of viruses it takes to establish and produce an infection is relatively large. Unlike measles, which just needs a few, with this coronavirus, you may need prolonged contact for enough virus to get transmitted.” Indoor settings also aid transmission of the virus, Riley said. Outdoor breezes quickly scatter airborne virus, thinning their concentration, and sunlight destroys them after about a half-hour. Indoors, concentrated virus can linger in the air much longer and survive on some surfaces for days. That explains why so many outbreaks occur at institutional settings like jails, prisons and elder care homes, where inmates and residents remain inside together in large numbers and share many facilities. It also explains clusters of cases among crowded, multigenerational households and large family gatherings. “The virus has the potential to hang around longer than it does outdoors, where the wind’s blowing,” Riley said. For the same reason, California’s efforts to close down parks and other outdoor gathering spots may have been overkill, when health officials should have been focusing on controlling the spread in congregate living and work settings, experts say. How the risk shakes out for businesses is less clear, as some deemed essential and allowed to remain open during the lockdown seem to be harder hit than others. The U.S. Centers for Disease Control and Prevention this month reported that 4,913 workers in 115 meat and poultry plants employing 130,000 workers in 19 states have tested positive for the disease and 20 have died, despite sanitation and social distancing measures for these essential food businesses. Why meat plants? The CDC said it’s hard for those workers to stay separated and wear masks on the job, and there are “sociocultural and economic challenges” with a diverse, lowwage workforce, including language barriers and employees living in crowded settings and sharing rides to work. Supermarkets and grocery stores, however, seem to have suffered fewer and smaller outbreaks. The United Food and Commercial Workers union said 5,500 of its grocery employee members have been infected nationally. FMI, the food industry association representing major grocery chains, did not dispute the figure, which is less than a tenth of a percent of the industry’s total workforce of 6 million. But health officials don’t track COVID-19 outbreaks at private businesses like they do for elder care and correctional facilities, so what is known about them is only what the companies disclose or surfaces in news accounts. At least one California grocery chain said infections have been minimal. Raley’s, which includes Bel Air Markets and Nob Hill Foods, said there have been just four cases among its 13,000 employees at four of its 126 stores; all of the infections were in the Sacramento area. But the question remains — beyond these known clusters, how did the tens of thousands of Californians who aren’t accounted for in publicized major outbreaks become infected? Before the rapid rise in cases prompted the lockdowns in mid-march, public health officials flagged cases with no known exposure to the virus through infected people or foreign travel as “community transmission.” But most counties have since stopped reporting that. And that means we’re still not certain of the threat from handling the gas pump or from the jogger huffing and puffing past us on the park trail. “We don’t know if people just going to parks or beaches, just sort of casual social gathering, contribute a whole lot to infections,” Riley said. Public health officials “really need to identify the high-transmission settings and then target those and not have these unfocused measures on social distancing.” While local health departments are focusing major efforts on “contact tracing” people who have been exposed to infections, experts say they should be providing the public with information about the infections to help us understand the risks. “Contact tracing data needs to be reported by setting,” said Dr. Rajiv Bhatia, assistant professor of primary care and population health at Stanford University and San Francisco’s former director of occupational and environmental health. “If we can get that together for California and for the nation, we can tell people what the relative risks are. Do we see infections in schools? If not, then maybe schools are safer.” Bhatia said public health officials have more information than they’ve shared publicly about where people are being infected. He has filed public records requests for the data. Alameda, Contra Costa and San Mateo county health departments either did not respond or did not have information about other workplace clusters. Santa Clara County said that besides longterm care facilities there haven’t been other undisclosed clusters like the Lusamerica plant. However, a study in March mentioned five people infected in association with an outbreak at an unidentified “large facility with multiple employers, large areas of shared space, and heavy pedestrian traffic.” “There’s a public safety interest in knowing where the infections are coming from and knowing the relative risks in different places,” Bhatia said. “When any location is associated with an outbreak, it’s important for the public to know — period.”