Dangerous Blood Clots Pose a Perplexing Coronavirus Threat

First came a high fever, drenching sweats and muscle aches. Then, almost a month later, a weird numbness that spread down the right side of her body.

Darlene Gildersleeve thought she had recovered from COVID-19. Doctors said she just needed rest. And for several days, no one suspected her worsening symptoms were related — until a May 4 video call, when her physician heard her slurred speech and consulted a specialist.

“You’ve had two strokes,” a neurologist told her at the hospital. The Hopkinton, New Hampshire, mother of three is only 43.

Blood clots that can cause strokes, heart attacks and dangerous blockages in the legs and lungs are increasingly being found in COVID-19 patients, including some children. Even tiny clots that can damage tissue throughout the body have been seen in hospitalized patients and in autopsies, confounding doctors’ understanding of what was once considered mainly a respiratory infection.

“I have to be humble and say I don’t know what’s going on there, but boy we need to find that out because unless you know what the pathogenic (disease-causing) mechanism is, it’s going to be tough to do intervention,” Dr. Anthony Fauci, the nation’s top infectious disease expert, remarked during a medical journal interview last month.

Doctors and scientists at dozens of hospitals and universities around the globe are seeking answers while trying to measure virus patients’ risks for clots and testing drugs to treat or prevent them.

Gildersleeve said health authorities “need to put out an urgent warning about strokes” and coronavirus. Not knowing the possible link “made me doubt myself” when symptoms appeared, she said.

Some conditions that make some COVID-19 patients vulnerable to severe complications, including obesity and diabetes, can increase clot risks. But many authorities believe how the virus attacks and the way the body responds both play a role.

“COVID-19 is the most thrombotic (clot-producing) disease we’ve ever seen in our lifetime,” said Dr. Alex Spyropoulos, a clot specialist and professor at Feinstein Institutes for Medical Research in Manhasset, New York.

Clotting has been seen in other coronavirus infections, including SARS, but on a much smaller scale, he said.

Scientists believe the coronavirus enters the body through enzyme-receptors found throughout the body, including in cells lining the inside of blood vessels. Some theorize that it may promote clotting by somehow injuring those vessels as it spreads. That injury may cause a severe immune response as the body tries to fight the infection, resulting in inflammation that may also damage vessels and promote clotting, said Dr. Valentin Fuster, director of Mount Sinai Heart hospital in New York.

It’s unclear how many COVID-19 patients develop clots. Studies from China, Europe and the United States suggest rates ranging from 3% to 70% of hospitalized COVID-19 patients; more rigorous research is needed to determine the true prevalence, the National Institutes of Health says.

Prevalence in patients with mild disease is unknown and the agency says there isn’t enough evidence to recommend routine clot screening for all virus patients without clotting symptoms, which may include swelling, pain or reddish discoloring in an arm or leg.

Some hospitals have found 40% of deaths in COVID-19 patients are from blood clots. Spyropoulos said that’s been true at his 23-hospital system in the New York City area, Northwell Health, which has treated over 11,000 COVID-19 patients.

Cases there have dropped by almost half in the past month, allowing more time for research before an expected second and maybe third wave of infections, he said, adding: “We’re racing against time to answer the key clinical questions.”