In Massachusetts, the young man admitted to the Newton-Wellesley hospital was very sick, as much as he needed a ventilator to breathe.
The doctors around him were sure he had the new coronavirus. In mid-April, the patient had trouble breathing and had other symptoms.
However, the first test for coronavirus came back negative. 24 hours later, another test came up negative. The doctors decided to follow another approach.
Dr. Michael Misialek, a pathologist at Newton-Wellesley Hospital outside Boston, decided to carry out a tracheal aspirate.
It is a test that gathers samples from deeper in the respiratory system. It is a different technique, however, health experts reported that they can't find evidence of COVID-19 infection until they perform such tests.
This tracheal secretion came back positive and allowed the team to enroll the patient in a clinical trial. He was treated with one of several immune-based drugs being tried out on coronavirus patients, eventually recovered, and was discharged from hospital.
Similar cases happened around the world. In London, New York, and elsewhere, health workers were seeing patients arrive with severe symptoms, but then test negative for Covid-19.
Some studies are beginning to indicate that when patients are severely ill, the virus is replicating deeper in the respiratory system, beyond the reach of the swabs used for most of the testing, experts say.
Dozens of tests are on the market, but their reliability varies greatly.
Polymerase chain reaction (PCR) tests, which look for evidence of the virus, are usually reliable, but not always.
