One in five adult COVID survivors under age 65 in the United States has experienced at least one health condition that could be considered long COVID, according to a large new study by the Centers for Disease Control and Prevention. Among patients 65 and older, the number is even higher: one in four.

In an indication of how seriously the federal health agency views the problem of long COVID, the authors of the study — members of the CDC's COVID-19 Emergency Response Team — recommended "routine assessment for post-COVID conditions among persons who survive COVID-19."

Long COVID is the term used to describe an array of symptoms that can last for months or longer after the initial coronavirus infection. The researchers identified post-COVID health problems in many different organ systems, including the heart, lungs and kidneys. Other issues involved blood circulation, the musculoskeletal system and the endocrine system; gastrointestinal conditions, neurological problems and psychiatric symptoms were also identified in the study.

In both age groups, COVID patients had twice the risk of uninfected people of developing respiratory symptoms and lung problems, including pulmonary embolism, the study found. Post-COVID patients ages 65 and older were at greater risk than the younger group of developing kidney failure, neurological conditions and most mental health conditions.

"It is sobering to see the results of this study again confirming the breadth of organ dysfunction and the scale of the problem," said Dr. Ziyad Al-Aly, chief of research and development at the VA St. Louis Health Care System and a clinical epidemiologist at Washington University in St. Louis, who was not involved in the research.

The study evaluated electronic medical records for nearly 2 million people — comparing those who had been infected with the coronavirus with those who were not. The most common post-COVID conditions, regardless of age, were respiratory problems and musculoskeletal pain.

The risk of post-COVID patients ages 65 and older developing the 26 health conditions the study evaluated was between 20% and 120% greater than people who didn't get COVID. Those ages 18-64 had a 10% to 110% greater risk than uninfected people of developing 22 of the health conditions. But in that age group, COVID survivors were no more likely than uninfected people to develop most mental health conditions, substance use disorders or strokes and similar cerebrovascular conditions.

Al-Aly said the study results "can potentially translate into millions of people with new diabetes, heart disease, kidney disease, neurologic problems. These are lifelong conditions — certainly manageable, but not curable conditions."

The study analyzed records of 353,164 people who were diagnosed with COVID-19 in the first 18 months of the pandemic, beginning in March 2020. It compared them with the records of 1.64 million people who had a medical visit in the same month in which the COVID patients were diagnosed but did not become infected with the coronavirus during the study period, which ended on Oct. 31, 2021.

People in both groups who had a history of one of the 26 health conditions in the previous year were excluded from the study — an attempt by the researchers to consider medical issues that patients developed only after they had COVID.

The study, which involved patients seen at health facilities that use a record system managed by Cerner Corp., a large medical data company, said the COVID patients included people admitted to hospitals, seen in emergency departments or diagnosed in an outpatient setting. The researchers did not indicate how many patients were in each group, one of several limitations of the study's findings.

Between 30 days and 365 days after their coronavirus diagnosis, 38% of the patients experienced one or more new health problems, compared with 16% of the non-COVID patients, the study said. The younger age group, 18 to 64, was somewhat less likely to have those problems — 35% developed long COVID issues, compared with 15% of uninfected people. In the 65-and-older group, 45% had new health conditions, compared with 19% of uninfected people.

Based on those percentages, the study authors calculated that nearly 21% of the younger group and nearly 27% of the older group developed health problems that could be attributed to long COVID.

The study did not look at the vaccination status of the patients and did not report characteristics such as race, ethnicity, sex or geographic location. It also did not identify which coronavirus variants were linked to each case.

The CDC authors concluded that post-COVID conditions might "affect a patient's ability to contribute to the workforce and might have economic consequences for survivors and their dependents." They added that "care requirements might place a strain on health services" in "communities that experience heavy COVID-19 case surges."

Al-Aly said he agreed that people who had COVID should be medically evaluated for potential new health problems.

"Now that we are in possession of knowledge that COVID-19 can lead to serious long-term consequences," he added, "we need to develop additional tools to reduce the risk of long COVID."

This article originally appeared in the New York Times.