Abbott Test May Curb Virus Even Missing Some Cases, CDC Says

(Bloomberg) -- Abbott Laboratories’ BinaxNOW, a 15-minute test for Covid-19, may miss nearly two-thirds of infections in those without symptoms, but its turnaround time and affordability make it a potentially useful tool for keeping the virus from spreading, according to a federal study.

The study evaluated results from 3,419 people tested in November with both BinaxNOW and the gold-standard PCR method that detects the genetic makeup of the virus in Pima County, Arizona. The result offers one of the first real-world examinations of how the two approaches stack up against each other.

BinaxNOW, called an antigen test, detected the virus in 64% of those who had symptoms and were positive using the PCR testing approach. But it identified just 36% of those who didn’t have any clear signs of the virus. Both tests accurately ruled out infections in almost all of those who weren’t carrying the virus.

The report was included in the Morbidity and Mortality Weekly Report for the Centers for Disease Control and Prevention. The researchers said the speed and low cost of BinaxNOW, priced at $5 for health care providers and $25 for consumers who have it shipped to their homes, makes it a good way to repeatedly test fixed groups to catch people at their most infectious.

“Despite a lower sensitivity to detect infection, rapid antigen tests can be an important tool for screening because of their quick turnaround time, lower costs and resource needs,” the CDC said in its report.

The 15-minute turnaround time and inexpensive costs can be valuable in limiting transmission when used for serial testing in settings like elementary, middle and high schools, colleges or other places people live in group housing, according to the CDC.

Abbott shares rose 1.5% to $112.57 in New York trading on Tuesday.

‘Powerful Tool’

BinaxNow is a “powerful tool in preventing transmission compared to a 24-hour turnaround PCR test,” said Kim Modory, an Abbott spokeswoman in a statement. The company’s latest studies show BinaxNOW correctly identifies positive cases of Covid-19 84.6% of the time, she said, with better performance in those who are most likely to be infectious.

“During a pandemic, having a rapid antigen test like BinaxNOW gives the patient critical information at a point in the infection cycle when they’re at the highest risk of spreading disease,” Modory said.

The CDC study will likely continue to fuel controversy over the usefulness of antigen tests and how they should be used. While they carry advantages, critics have questioned their reliability, particularly among test-seekers who lack symptoms.

Key Metric

Proponents, meanwhile, argue that antigen tests perform better than the gold-standard PCR tests on a key metric -- detecting individuals who are likely to transmit the coronavirus to others -- when used frequently over a period of time.

Both sides will find support for their positions in the CDC report. In addition to testing swabs from patients with both antigen and PCR tests, researchers also cultured virus from 274 positive patient samples, a technique that’s been used as a proxy for measuring infectiousness.

They found that BinaxNOW’s performance was significantly better for samples with a positive virus culture, detecting 79% of those without symptoms and 93% of those who were actively ill, “which might reflect better performance for detecting infection in a person with infectious virus present,” according to the CDC study.

Misleading Conclusion

Michael Mina, a Harvard epidemiologist who has called for making rapid tests like Abbott’s BinaxNOW widely available, described the CDC study and its conclusions as misleading in an emailed statement. The comparison failed to take into account that PCR tests sometimes needlessly raise concern when they detect viral particles days or even weeks after they’re capable of causing infections, he said.

Mina compares the two types of tests to a forensics detective versus a security guard.

“The forensics detective can find the DNA in a piece of hair or a drop of blood for weeks after the crime has been committed,” he said. “But it’s crazy to ask a security guard to do this. The guard is there only to find a crime that is currently being committed.”

Overwhelmed Laboratories

Tests like BinaxNOW, which detect a specific viral antigen and work within 15 minutes, may be particularly useful when PCR tests aren’t available or when laboratories are overwhelmed and take days or weeks to generate results, the CDC said.

“Persons who know their positive test result with 15-30 minutes can isolate sooner, and contact tracing can be initiated sooner and be more effective than if a test result is returned days later,” the agency concluded. “Serial antigen testing can improve detection, but consideration should be given to the logistical and personnel resources needed.”

Everyone who gets a negative coronavirus test result, regardless of which type of diagnostic they receive, should be told that wearing a mask, avoiding close contact with others and washing their hands often is critical to avoiding the spread of coronavirus, the agency said.

(Adds epidemiologist’s comment starting in the 14th paragraph)