Are there better ways to track Covid cases?

When the transmissible Omicron variant of the coronavirus arrived in the United States last fall, it pushed the numbers of new cases to levels not seen before.

Until then, the record wave of recorded infections was actually quite a shortage.

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

The official number of coronavirus infections in the United States has always been an underestimate. But with Americans increasingly turning to home testing, and states closing mass testing sites and institutions reducing surveillance testing, the number of cases is becoming an increasingly unreliable measure of the true number of the virus, scientists say.

“Blind spots appear to be getting worse over time,” said Dennis 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 published.

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

The official case count can still capture major trends, and it’s starting to rise again with BA.2 spreads. But experts say reductions in numbers are likely to be an even bigger problem in the coming weeks, and mass testing sites and large-scale monitoring testing may never return.

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

To track BA.2, as well as future variables, officials will need to extract any possible insights from a set of current indicators, including hospitalization rates and wastewater data. Really monitoring the virus will require more creative thinking and investment, the scientists said.

Right now, some scientists said, people can gauge their risk by using a low-tech tool: paying attention to whether people they know have the virus.

“If you hear your friends and co-workers getting sick, it means your risk is high and that means you probably need to be tested and hidden,” said Samuel Scarpino, vice president of pathogen control at the Rockefeller Pandemic. Prevention Institute.

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

By the time Omicron started, a new challenge was emerging: At-home tests were finally widely available, and many Americans relied on them for their winter vacation. Many of these results have not been reported.

“We haven’t done the groundwork to systematically capture these cases at the national level,” said Catelyn Getelina, an epidemiologist at the University of Texas Health Science Center at Houston.

Some jurisdictions and test manufacturers have developed digital tools that allow people to report their test results. But one recent study suggests that it may take effort to get people to use them. Residents of six communities across the country have been invited to use an app or online platform to request free tests, record their results, and then, if they choose, send that data to state health departments.

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

Experts have said that the general fatigue of Covid, in addition to the protection offered by vaccination against severe symptoms, may lead fewer people to seek the test. Lacking funds, the federal government recently announced that it would stop reimbursing health care providers for the cost of testing uninsured patients, prompting some providers to stop offering these tests for free. Dr. said.

She noted that “poorer neighborhoods will have lower case numbers than high-income neighborhoods.”

Monitoring case trends remains important, experts said. said Alyssa Belinsky, a public health policy expert at Brown University’s School of Public Health.

But experts said more modest increases in transmission may not be reflected in the number of cases, which means officials may take longer to detect new spikes. The problem can be exacerbated by the fact that some jurisdictions have started updating their case data less frequently.

Dr. Nash and his colleagues are exploring ways to overcome some of these challenges. To estimate how many New Yorkers might have been infected during the Omicron winter wave, they surveyed a diverse sample of 1,030 adults about testing behaviors and outcomes, as well as potential exposure to Covid-19 and symptoms.

People who reported testing positive for the virus in tests by health care providers or testing were counted as cases that would have been detected by standard surveillance systems. Only those who tested positive for the virus at home were counted as hidden cases, as were those with potential unreported infections – a group that included people with Covid-19-like symptoms and known exposure 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.

Study has limits. It is based on self-reported data and excludes children, as well as adults living in institutions, including nursing homes. Dr Nash said health departments could use the same approach to try to fill in some blind spot control, especially during sudden surges in current.

“You can run these surveys on a daily or weekly basis and quickly correct prevalence estimates in real time,” he said.

Another way would be to repeat what Britain did, regularly testing a random group of hundreds of thousands of residents. “These are really Cadillac methods of monitoring,” said Natalie Dean, a biostatistician at Emory University.

However, this method is expensive, and Britain has recently begun to scale back its efforts. “It’s something that should be part of our arsenal in the future,” said Dr. Dean. “It’s kind of unclear what people would like.”

The spread of Omicron, which easily infects vaccinated people and generally causes milder disease than the previous Delta variant, has prompted some officials to focus more on hospitalization rates.

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

Dr Salmi said hospitalization rates are late and may not reflect the true toll of the virus, which can cause serious and prolonged Covid disruptions without sending people to hospital.

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

But the Centers for Disease Control and Prevention’s community transmission map, which is based solely on local cases and test-positive rates, indicates that only 29 percent of US counties currently have low levels of transmission of the virus.

Hospitalization data may be reported differently from place to place. Because Omicron is highly contagious, some regions are trying to specifically differentiate patients who have been hospitalized to Covid-19 and those who caught the virus by chance.

Jonathan Ballard, chief medical officer of the New Hampshire Department of Health and Human Services, said.

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

Another solution is to use approaches, such as wastewater monitoring, that do not rely on testing or access to healthcare at all. People with coronavirus infection shed the virus in their faeces; Monitoring virus levels in wastewater provides an indication of the extent of its spread in the community.

“And then you combine that with the sequencing, so you get an idea of ​​what variables are circulating,” said Dr. Andersen, who works with colleagues to trace the virus in San Diego wastewater.

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

“Wastewater is a no-brainer,” said Dr. Andersen. “It gives us a really good and important passive control system that can be expanded. But only if we realize that is what we have to do.”

Dr. Scarpino, of the Institute for Epidemic Prevention, said there were other data sources officials could draw on, including information on school closures, flight cancellations and geolocation.

“One of the things we’re not doing well enough is bringing those together in a deliberate, coordinated way,” said Dr. Scarpino.

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