The number of New Jerseyans who currently have or have ever had COVID-19 has grown by more than 50,000, now that the Department of Health is reporting positive antigen test results that indicate likely cases of the virus.
While the state COVID-19 Dashboard on Tuesday reported just shy of a half-million confirmed cases of the disease caused by the novel coronavirus from so-called PCR tests, that total jumps to 551,419 when close to 52,000 antigen test results are added. If all of those additional positive results are accurate, that would mean more than six of every 100 residents have been infected since the state’s first case 10 months ago.
Since the first positive case of COVID-19 in Bergen County last March 4, state health officials had been reporting results only of tests done using a nasal swab and checked in a lab using a technique known as polymerase chain reaction, or PCR — the only test available at first. Even after antigen testing, which may test nasal secretions or saliva, became more readily available, the state did not report those results for a number of reasons, including that they are less accurate and there was no easy way for the Department of Health to get all the results.
Ordering COVID-19 test kits online
The U.S. Centers for Disease Control and Prevention says the tests are somewhat less accurate, but they are less expensive and can provide results within 15 minutes, as opposed to several days to a week for PCR tests. People can now order a test kit online and test themselves at home, as the U.S. Food and Drug Administration has given an emergency-use authorization to a handful of kits.
Stephanie Silvera, an epidemiologist at Montclair State University, said coronavirus antigen tests are like over-the-counter home pregnancy screenings with some limits to their accuracy, while the PCR tests are equivalent to a blood test to confirm pregnancy. It takes time for the COVID-19 proteins identified by the antigen test to develop in the blood, she explained, while PCR tests are more sensitive and therefor more accurate. With an antigen test, “when it’s positive, you’re positive, but if it’s negative you still might be positive,” she said.
The state released the first data, which appears to date back to May 1 at least, on Monday both on a statewide and county-by-county basis. Between Monday and Tuesday, the number of positive antigen tests increased by almost 1,000.
In announcing the decision to report positive antigen test results as probable COVID-19 infections, Health Commissioner Judith Persichilli explained the benefits and drawbacks of the two tests and said the state had decided to start reporting positive antigen test results. It is unclear, though, how many such results the state is getting.
“Because of its ease of use, antigen tests are available in many settings, some of which are not accustomed to reporting data to the department,” she said. “We continue to connect these entities to our reporting database to get a fuller picture of the tests conducted, and those coming back positive, to enhance our knowledge of disease spread in the state.”
Limited use of negative antigen tests
The dashboard indicates that negative antigen test results are less likely to be reported so this data cannot be used to determine a positivity rate or how many total tests are being conducted in the state. Currently, the dashboard shows that more than 8 million PCR test results have been conducted, which is approaching the size of the state’s population.
Silvera said the addition of the antigen test numbers to the state’s reporting system is helpful, but the data still doesn’t tell the full story.
“Anytime there is more data that can help us determine what the community spread is, that’s good,” she said. PCR and antigen results “combined together is probably a better picture of what is happening,” she added, noting these numbers still don’t reflect all those New Jerseyans who are infected.
The state dashboard indicates this as well, noting: “Unlike PCR testing, most antigen tests are performed outside of central laboratories and therefore need to be reported manually to public health authorities. As a result, the number of reported positive antigen tests greatly underestimates the total number of positive tests performed.”
Silvera said antigen tests are best suited for ongoing disease surveillance,like daily or regular testing at a workplace or nursing home, where they can be used to track changes in the same population over time. The DOH provided tens of thousands of rapid BinaxNOW rapid antigen tests to nursing homes last fall to help them monitor and control the virus after federal officials pledgedto provide the state some 2.6 million of these tests at no cost.
“There’s a role for each of (these tests), but it’s thinking about what you are using them for,” Silvera said. “I wouldn’t use the antigen test on a Friday and say I’d get together (with a group of people) on a Saturday.”
— Lilo H. Stainton contributed to this story