As SARS-CoV-2 spread through New York City in late March, doctors at Mount Sinai Hospital noticed something strange happening to patients’ blood.

Signs of blood clotting were being detected in different organs by doctors from different specialties. This would turn out to be one of the alarming ways the virus ravages the body, as doctors there and elsewhere were starting to realise.

At Mount Sinai, nephrologists noticed kidney dialysis catheters getting plugged with clots. Respiratory physicians monitoring COVID-19 patients on mechanical ventilators could see portions of lungs were oddly bloodless. Neurosurgeons confronted a surge in their usual caseload of ischaemic strokes, the age of victims skewing younger, with at least half testing positive for the virus.

“It’s very striking how much this disease causes clots to form,” Dr J Mocco, a Mount Sinai neurosurgeon, said in an interview, describing how some doctors think COVID-19 is more than a lung disease. In some cases, Dr Mocco said, a stroke was a young patient’s first symptom of the disease.