The number of new daily Covid-19 cases in the United States has more than quadrupled over the past month—but many public health experts warn that even these figures are likely an undercount, particularly as more people rely on rapid at-home tests that often aren't officially reported.

The policies Biden and states could use to control the omicron variant

Covid-19 cases hit record highs, but they're likely undercounted

Over the past week, the country has averaged more than 401,000 new cases a day, according to a New York Times database—up from an average of around 83,000 at the beginning of December.

The omicron variant: The 'good,' 'bad,' and 'ugly' scenarios

However, several public health experts have said the true number of new Covid-19 cases is likely even higher, particularly as pharmacies and testing sites become overwhelmed and more people diagnose themselves using rapid at-home tests.

Unlike the results of PCR tests, which are reported to public health authorities and included in confirmed case counts, the results of rapid tests often go unreported. And according to some experts, this underreporting of Covid-19 cases may affect public guidance health.

"We certainly don't want to discourage [rapid] testing, but at the same time we can't leave public health authorities blind," said Mara Aspinall, an expert in biomedical diagnostics at Arizona State University. "They rely on this information to take proactive and reactive precautions. It's a very fine balance."

Rachel Rubin, senior medical officer for the Cook County Department of Public Health in Illinois, said while at-home testing has had a positive effect by allowing people to isolate when necessary, it has also left public health officials in the dark about many infections. In particular, she said if positive rapid tests administered at schools and nursing homes are not reported, officials will have difficulties providing guidance on isolation procedures or identifying other cases connected to an outbreak.

"It's sort of like a double-edged sword," Rubin said. "I think we are only capturing the tip of the iceberg of positive tests."

How public health officials plan to track Covid-19 cases going forward

As Americans continue to rely on rapid tests, CDC said it is currently working with rapid test manufacturers to improve people's ability to report their results to health authorities, Newsweek reports.

Instead of tracking Covid-19 cases through daily case rates, some public health officials are considering moving towards less frequent case reporting or a "sentinel surveillance" system, which tracks instances of the disease through a network of health care centers, the Times reports.

Marcelle Layton, CMO of the Council of State and Territorial Epidemiologists, said the organization has discussed moving away from daily case counts in the coming months and has been in contact with CDC about potential guidance directing states to limit daily case reporting. "Everyone knew that this time was coming," Layton said, noting that this shift is part of an approach to treat Covid-19 as an endemic disease, much like influenza.

As the limitations of daily Covid-19 case counts become more apparent, some local public health officials are now turning to other sources, such as hospitalization trends and direct reports from community leaders, to track the spread of the virus.

"With the situation we're in for with something as aggressive as omicron, testing, isolation, and contact tracing become much less relevant," said Jessica Guernsey, health director for the Multnomah County Public Health Department in Oregon. "At some point, the sort of constant drumbeat of understanding that there's a lot of Covid out there—it doesn't help us understand things that much more." (Kolata/Kambhampaty, New York Times, 1/3; Findlay, The Hill, 12/29/21; Kasakove, New York Times, 12/30/21; Fink, Newsweek, 12/30/21; DeBarros/Hookway, Wall Street Journal, 12/30/21)