Are There Better Ways to Track Covid Cases?

When the highly transmissible Omicron variant of the coronavirus arrived in the United States last fall, it pushed the number of new cases to unprecedented heights.

Even then, the record wave of reported infections was a significant understatement of reality.

In New York City, for example, officials recorded more than 538,000 new cases between January and mid-March, representing about 6 percent of the city’s population. But a recent survey of New York adults suggests there could be more than 1.3 million additional cases that were never detected or never reported, and that 27 percent of the city’s adults may have been infected during those months.

The official count of coronavirus infections in the United States has always been an underestimate. But as Americans increasingly turn to at-home testing, states close mass testing sites, and institutions scale back surveillance testing, case counts are becoming an increasingly unreliable measure of the number. number of virus victims, scientists say.

“The blind spots seem to be getting worse over time,” said Denis Nash, an epidemiologist at the CUNY Graduate School of Public Health and Health Policy who led the New York City analysis, which is preliminary and not yet available. Has published.

That could leave officials increasingly in the dark about the spread of the highly contagious new subvariant of Omicron known as BA.2, he said, adding: “We are more likely to be surprised.” On Wednesday, New York officials announced that two new Omicron subvariants, both descendants of BA.2, have been circulating in the state for weeks and are spreading even faster than the original version of BA.2.

The official case count may still follow major trends, and has started to rise again as BA.2 spreads. But undercounts are likely to be a bigger problem in the coming weeks, experts said, and mass testing sites and widespread surveillance testing may never return.

“That’s the reality we find ourselves in,” said Kristian Andersen, a virologist at the Scripps Research Institute in San Diego. “We don’t really have our eyes on the pandemic like we used to.”

To track BA.2, as well as future variants, officials will need to get as much information as they can from a number of existing indicators, including hospitalization rates and sewage data. But really getting the virus under control will require more creative thinking and investment, the scientists said.

For now, some scientists said, people can gauge their risk by implementing a low-tech tool: paying attention to whether people they know are contracting the virus.

“If you hear about your friends and your co-workers getting sick, that means your risk is higher and that means you probably need to get tested and mask up,” said Samuel Scarpino, vice president of pathogen surveillance at Pandemic at the Rockefeller Foundation. Prevention Institute.

Tracking the virus has been a challenge since the early days of the pandemic, when testing was severely restricted. Even when testing improved, many people didn’t have the time or resources to look for it, or had asymptomatic infections that never made themselves known.

When Omicron arrived, a new challenge presented itself: home testing was finally more widely available and relied on by many Americans to get them through the winter holidays. Many of those results were never reported.

“We haven’t done the legwork to systematically capture those cases nationally,” said Katelyn Jetelina, an epidemiologist at the University of Texas Health Sciences Center in Houston.

Some jurisdictions and test manufacturers have developed digital tools that allow people to report their test results. But a recent study suggests it can take work to get people to use them. Residents in six communities across the country were invited to use an app or online platform to request free tests, record their results, and then, if they wanted, submit that data to their state health departments.

Nearly 180,000 households used the digital assistant to order tests, but only 8 percent of them recorded any results on the platform, the researchers found, and only three-quarters of those reports were sent to health officials.

General Covid fatigue, as well as the protection vaccination provides against severe symptoms, may also cause fewer people to seek testing, experts said. And citing a lack of funding, the federal government recently announced it would stop reimbursing health care providers for the cost of testing uninsured patients, prompting some providers to stop offering those tests for free. That could make uninsured Americans especially reluctant to get tested, Dr. Jetelina said.

“Poorer neighborhoods will have even more depressed case numbers than high-income neighborhoods,” he noted.

Tracking case trends remains important, experts said. “If we see an increase in cases, it’s an indicator that something is changing, and quite possibly something is changing due to a larger shock to the system, like a new variant,” said Alyssa Bilinski, a public health policy expert. from the Brown University School of Public Health.

But more modest increases in transmission may not be reflected in case counts, meaning it could take longer for officials to spot new surges, experts said. The problem could be exacerbated by the fact that some jurisdictions have begun to update their case data less frequently.

Dr. Nash and his colleagues have been exploring ways to overcome some of these challenges. To estimate how many New Yorkers may have been infected during Omicron’s winter surge, they surveyed a diverse sample of 1,030 adults about their behaviors and test results, as well as potential exposures and symptoms of Covid-19.

People who reported testing positive for the virus on tests administered by health care or testing providers were counted as cases that would have been detected by standard surveillance systems. Those who tested positive only in home tests were counted as hidden cases, as were those with unreported probable infections, a group that included people who had COVID-19-like symptoms and known exposures to the virus.

The researchers used the responses to calculate how many infections might have escaped detection, weighting the data to match the demographics of the city’s adult population.

The study has limitations. It is based on self-reported data and excludes children as well as adults living in institutional settings, including nursing homes. But health departments could use the same approach to try to fill in some of their surveillance blind spots, especially during spikes, Dr. Nash said.

“You could do these surveys daily or weekly and quickly correct the prevalence estimates in real time,” he said.

Another approach would be to replicate what Britain has done, regularly testing a random selection of hundreds of thousands of residents. “That’s really the Cadillac of surveillance methods,” said Natalie Dean, a biostatistician at Emory University.

However, the method is expensive and Britain has recently started to scale back its efforts. “It’s something that should be part of our arsenal in the future,” Dr. Dean said. “It’s not clear what people have an appetite for.”

The spread of Omicron, which easily infects even vaccinated people and generally causes milder illness than the earlier Delta variant, has prompted some officials to put more emphasis on hospitalization rates.

“If our goal is to track serious illness from the virus, I think that’s a good way to do it,” said Jason Salemi, an epidemiologist at the University of South Florida.

But hospitalization rates are lagging indicators and may not capture the true death toll from the virus, which can cause severe disruption and a long period of Covid without sending people to hospital, Dr. Salemi said.

In fact, different metrics can create very different risk portraits. In February, the Centers for Disease Control and Prevention began using local hospitalization rates and measures of hospital capacity, in addition to case counts, to calculate its new “community Covid-19 levels,” which are designed to help people decide whether to wear masks. or take other precautions. More than 95 percent of US counties currently have low levels of COVID-19 in the community, based on this measure.

But the CDC’s community transmission map, which is based solely on local cases and test positivity rates, suggests that only 29 percent of US counties currently have low levels of viral transmission.

Hospitalization data may be reported differently from place to place. Because Omicron is so transmissible, some localities are trying to distinguish between patients who were hospitalized specifically for Covid-19 and those who picked up the virus incidentally.

“We felt that due to the intrinsic factors of the very virus that we are seeing circulating in our region now, we needed to update our metrics,” said Dr. Jonathan Ballard, medical director of the New Hampshire Department of Health. Health and Human Services.

As of late last month, New Hampshire’s online Covid-19 dashboard was showing all hospitalized patients with active coronavirus infections. Now, instead, it shows the number of hospitalized covid-19 patients taking remdesivir or dexamethasone, two first-line treatments. (Data on all confirmed infections in hospitalized patients remain available through the New Hampshire Hospital Association, Dr. Ballard noted.)

Another solution is to use approaches, such as sewage surveillance, that do not rely on testing or access to health care at all. People with coronavirus infections shed the virus in their stool; monitoring virus levels in wastewater provides an indicator of how widespread it is in a community.

“And then you combine that with sequencing, to get a sense of what variants are circulating,” said Dr. Andersen, who is working with colleagues to track the virus in San Diego sewage.

The CDC recently added wastewater data from hundreds of sampling sites to its Covid-19 dashboard, but coverage is highly patchy, with some states reporting no current data at all. If wastewater monitoring is going to fill testing gaps, it needs to be expanded and the data published in near real time, the scientists said.

“Sewage is a no-brainer for me,” Dr. Andersen said. “It gives us a really good and important passive surveillance system that can scale. But only if we realize that this is what we have to do.”

Dr. Scarpino, from the Pandemic Prevention Institute, said there were other data sources officials could tap into, including information on school closures, flight cancellations and geographic mobility.

“One of the things we’re not doing a good enough job of is bringing them together in a thoughtful and coordinated way,” Dr. Scarpino said.

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