As the new coronavirus spreads, doctors are seeing a pattern emerge in the way people are responding to the disease.
People at first will experience mild symptoms like a light cough or headache. After a week, those symptoms can escalate to a trip to the emergency room.
One ICU doctor said that COVID-19 patients "were doing okay, but at the five- to seven-day mark they got worse and then developed respiratory arrest in its true form."
As the novel coronavirus spreads, doctors are seeing a pattern in the way their patients are responding to the disease.
People who get sick tend to first suffer minor ailments, like headaches, light coughs, and a slight fever for around a week. But it's usually only at the end of the second week that they will either start improving, or suddenly decline, and for those who do get worse, it can quickly escalate to a trip to the emergency room.
For those who end up in the intensive care unit (ICU), there is a similar kind of delay in the way patients display symptoms and relapse after receiving treatments.
Michelle N. Gong, the director of critical care research at Montefiore Medical Center, said in a Q&A with the Journal of the American Medical Association on Monday that COVID-19 patients have often seemed to be "doing okay, but at the five- to seven-day mark they got worse and then developed respiratory arrest in its true form."
It's a quick onset, she said, "that can be very abrupt."
Many people who get the coronavirus feel fine for a week, then 'crash'
Critical care physician Dr. Joshua Denson told NBC News that, based on the 15-20 patients with coronavirus he has treated, he would describe the first phase of illness as "a slow burn."
Infectious disease specialist Dr. Christopher Ohl also told NBC that he's seen patients saying they think they're getting better, and "then within 20 to 24 hours, they've got fevers, severe fatigue, worsening cough and shortness of breath. Then they get hospitalized."
The CDC warns there is plenty of evidence, both published by researchers and anecdotal, that many patients see a "clinical deterioration during the second week of illness."
A study published in The Lancet in January found more than half of patients developed shortness of breath after already being ill for a week.
"It's known as the second-week crash," Donald G. McNeil Jr, a science and health reporter for The New York Times, said on The Daily podcast. "And some people crash even after they thought they were starting to get better."
Patients in hospital seem to get better before they get worse
A respiratory therapist told ProPublica that his "patients will be on minimal support, on a little bit of oxygen, and then all of a sudden, they go into complete respiratory arrest, shut down and can't breathe at all."
This sudden decline is most likely to happen for the most at-risk patients; the elderly and those with pre-existing health conditions.
With COVID-19 patients, unlike people with pneumonia or acute respiratory distress syndrome (ARDS), a disease where fluid builds up in the lungs, respiratory failure does not occur within the first few days of hospitalization. Gong added that there is a very high proportion of cardiac arrest in coronavirus patients, which may have to do with underlying conditions. "But, again, it's sudden, it's not yet predictable as to who will get it and who will not," she said.
Gong warned doctors not to use chloroquine, an immunosuppressive drug that can fight malaria, on their coronavirus patients. She understands that physicians may be desperate for a cure, but says it can cause more harm than good when used on coronavirus patients, given the medical establishment still doesn't know how it will react with coronavirus. Plus it could deprive patients who need the drug of their medicine.
"I still feel like we haven't seen the full extent," one internal medicine doctor previously told Business Insider. "It's like leaning over the edge of a cliff."