Dangerous blood clots pose a perplexing coronavirus threat

Tiny clots that can damage tissue throughout the body have been seen in hospitalized patients and in autopsies. This feature of the disease is confounding doctors' understanding of what was once considered mainly a respiratory infection. It's also raising questions about prevention and treatment. 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 play a role.