As coronavirus infections rise in some parts of the world, experts are watching a possible new surge of COVID-19 in the U.S. — and wondering how long it will take to detect it.

While disease surveillance has improved over the past two years, some recent developments do not bode well, they said:

— As more people get rapid COVID-19 tests at home, fewer people are getting the gold-standard test the government uses to count cases.

— The Centers for Disease Control and Prevention will soon use fewer labs to find new variants.

— Health officials are increasingly concerned about hospitalizations, which will only rise after a surge.

— Wastewater monitoring programs are still patchwork, and the data needed to understand the impending surge cannot yet be counted on.

— White House officials say the government has run out of money for vaccines, treatments and testing.

“We’re not in a good position,” said Jennifer Nuzzo, an epidemiology researcher at Brown University.

Scientists acknowledge that the widespread availability of vaccines and treatments has put countries in a better position than at the start of the pandemic, and that surveillance has come a long way.

For example, scientists this week touted a six-month project to test international travelers to four U.S. airports. Genetic testing of the samples on Dec. 14 found a variant of the coronavirus — a descendant of an omicron called BA.2 — seven days earlier than any other reported test result in the U.S.

More good news: U.S. cases, hospitalizations and deaths have fallen for weeks.

But it’s different elsewhere. The World Health Organization reported this week that the number of new coronavirus cases globally has increased for two weeks in a row, likely because many countries have stopped COVID-19 preventive measures and because BA.2 spreads more easily.

Some public health experts aren’t sure what this means for America

The CDC says BA.2 is making up a growing proportion of U.S. cases — more than a third nationwide and more than half in the Northeast. Both New York’s overall case rate and New England’s hospitalizations rose slightly.

However, Penn State’s Katriona Shea noted that some northern states with the highest BA.2 incidence rates have the lowest case rates.

Dr. James Musser, an infectious disease expert at Houston Methodist Church, called BA.2’s national case data “ambiguous.” “What we really need is as much real-time data as possible … to inform decision-making,” he added.

Here’s what COVID-19 trackers are working on and what worries scientists.

Test Results

Statistics of test results have been central to understanding the spread of the coronavirus from the beginning, but they have been flawed.

Initially, only patients were being tested, meaning the case count missed people who were asymptomatic or couldn’t get a swab test.

Home test kits became widely available last year, and when the omicron wave hit, demand started to take off. But many people who take home tests don’t report their results to anyone. Nor did the health agency try to collect them.

Mara Aspinall is a managing director at an Arizona consulting firm tracking trends in COVID-19 testing. She estimates that in January and February, an average of about 8 million to 9 million rapid home tests were performed a day — four to six times the number of PCR tests.

“The number of cases doesn’t reflect reality as much as it once did,” Nuzzo said.

look for variants

In early 2021, the U.S. was well behind other countries in using genetic tests to find worrisome viral mutations.

A year ago, the agency signed an agreement with 10 large laboratories to sequence the genome. The CDC will reduce the program to three labs over the next two months.

The volume of weekly serials executed through contracts was much higher during the omicron wave in December and January, when more people were tested, and it has dropped to around 35,000. By late spring, that number will drop to 10,000, although CDC officials say the contract allows the number to be increased to more than 20,000 if necessary.

The agency also said turnaround times and quality standards for new contracts have been improved, a change it doesn’t expect to hurt its ability to find new variants.

Outside experts have expressed concern.

“It really reduces the baseline surveillance and intelligence systems that we use to track what’s going on outside,” said Bronwyn MacInnis, director of genomic surveillance of pathogens at the Broad Institute of MIT and Harvard.

Sewage monitoring

An evolving surveillance system is looking for signs of the coronavirus in sewage, which could catch a brewing infection.

A week later, the researchers linked wastewater samples to the number of positive COVID-19 tests, suggesting that health officials can get an early look at infection trends.

Some health departments also use sewage to find variants.For example, New York City detected a signal of the omicron variant in a sample taken on Nov. 21 — about 10 days before the first case was reported in the U.S.

But experts point out that the system does not cover the entire country. It also cannot distinguish who is infected.

“There is no doubt that this is a very important and promising strategy. But the ultimate value may still be known,” said Dr. Jeff Duchin, health officer for Seattle/King County, Washington.

hospital data

Last month, the CDC outlined a new set of measures to decide whether to lift the mask-wearing mandate, focusing less on positive test results and more on hospitals.

The number of hospitalizations is a lagging indicator, given that it can take a week or more between infection and hospitalization. But some researchers think the change is appropriate. They say hospital data is more reliable and easier to interpret than case counts.

The lag is also not as long as one might think. Some studies show that many people wait to be tested. When they finally do, the results aren’t always immediate.

University of Texas data scientist Spencer Fox, who is part of a team using hospital and cellphone data to predict COVID-19 in Austin, said “hospitalizations are a better signal than test results.”

However, there are concerns about future hospital data.

A group of former CDC directors recently wrote that if the federal government rescinds its public health emergency declaration, officials would lose the ability to compel hospitals to report COVID-19 data. They urged Congress to pass a law giving enduring powers “so that we don’t risk blindness when a health threat arises.”