Covid-19 Live Updates: Opening of U.S. Education System Brings Strike Threats, New Cases and Improvisation

On Tuesday, New York City released more than 1.46 million coronavirus antibody test results, the largest number to date, providing more evidence of how the virus penetrated deeply into some lower-income communities while passing more lightly across affluent parts of the city.

Elsewhere in the United States:

• In Puerto Rico, where cases have been trending upward, Gov. Wanda Vázquez said she was imposing a lockdown that will apply on Sundays through Sept. 11, the latest in a series of escalating restrictions meant to keep people at home and not socializing with friends or family. Violators of the island’s mask order will be subject to a $100 fine. A nightly curfew remains in effect. Under the new Sunday order, Puerto Ricans will be allowed to leave their homes that day for only a handful of reasons, like going to grocery stores, pharmacies or hospitals, or working in essential services. Alcohol sales will be banned and beaches closed. Though houses of worship will be allowed to remain open at 25 percent capacity, Ms. Vázquez urged that religious services be held online.

• Apple reached $2 trillion in value, with half added in the past 21 weeks, while the global economy shrank faster than ever amid the pandemic.

• The 4,600 midshipmen, or students, at the U.S. Naval Academy in Annapolis, Md., began a mix of online and in-person classes on Wednesday, but not all of them will be on campus right away. About 500 students will be housed off campus because dormitory space has been set aside for those who may need to quarantine. The U.S. Military Academy at West Point, N.Y., which has more space, allowed all its cadets to be on campus when classes began Monday.

• The University of Notre Dame in Indiana, which moved to online instruction after a surge of cases, said Wednesday that it was pausing football practice for at least a day “in an abundance of caution.” The announcement came less than a day after Notre Dame said that athletic activities would continue during the university’s two-week run of remote learning. The football team is scheduled to begin its season on Sept. 12.

• Nevada reported on Wednesday that were 32 new deaths, a single-day record for the state.

U.S. health officials announce nationwide sewage testing for the virus.

Federal health officials announced a nationwide plan on Monday to begin testing sewage for the virus, as a potential measure of where the virus is spreading and at what rate. Infected people can pass the virus in their feces, and scientists are able to detect its levels in samples of wastewater from local sewage treatment centers.

In a statement, the Centers for Disease Control and Prevention said that it “is currently developing a portal for state, tribal, local, and territorial health departments to submit wastewater testing data into a national database for use in summarizing and interpreting data for public health action.” The program is intended to complement other measures, like clinical testing, not to replace them, the statement read.

Public health workers have analyzed sewage to track other viral outbreaks, like polio, for decades. The technology has advanced to a stage where it can estimate levels of the virus, providing a rough read on the prevalence of infections in an entire community.

The new initiative came days after New York’s governor announced a $500,000 wastewater testing pilot that would begin with samples from Albany, Newburgh and Buffalo, as well as from Onondaga County. On Tuesday, New York City’s mayor said that the city was eager to participate as the program expanded.

“The city is especially well positioned to use this technology because of our infrastructure,” he said.

Reporting was contributed by Sarah Almukhtar, Peter Baker, Alan Blinder, Alexander Burns, Benedict Carey, Choe Sang-Hun, Lynsey Chutel, Emily Cochrane, Nick Corasaniti, Thomas Erdbrink, Richard Fausset, Luis Ferré-Sadurní, Sheri Fink, Jacey Fortin, Katie Glueck, Joseph Goldstein, Jason Gutierrez, Anemona Hartocollis, Isayen Herrera, John Ismay, Mike Ives, Jennifer Jett, Anatoly Kurmanaev, Sharon LaFraniere, Apoorva Mandavilli, Alex Marshall, Jonathan Martin, Patricia Mazzei, Claire Cain Miller, Adam Nagourney, Jack Nicas, Elisabetta Povoledo, Frances Robles, Anna Schaverien, Christopher F. Schuetze, Eliza Shapiro, Jeanna Smialek, Sheryl Gay Stolberg, Eileen Sullivan, Jim Tankersley, Sheyla Urdaneta, Noah Weiland and Elaine Yu.