From Dr Tom Frieden, former director of the US Centers for Disease Control and Prevention

This photo taken on February 3, 2020 shows a medical staff member spraying disinfectant on a patient after returning from a hospital and re-entering a quarantine zone in Wuhan. STR/AFP via Getty Images)

A study published Friday in the medical journal JAMA found that 41% of the first 138 patients diagnosed at one hospital in Wuhan, China, were presumed to be infected in that hospital.

Why it's big news: In plain English, it means that nearly half of the initial infections in this hospital appear to have been spread within the hospital itself. This is called nosocomial transmission. (Doctors use big words to hide bad things: Nosocomial means caught it in the hospital.)

Super-spreader event seems unlikely: What's more, most spread doesn't appear to have been the result of a so-called "super-spreader event," in which a single patient transmits infection to many other people. In these events, a procedure such as bronchoscopy -- where a doctor inserts a tube into the patient's lungs -- can result in many infections.

This would be a concern, but not nearly as much as what appears to have happened: Many health care workers and many patients got infected in many parts of the hospital. What's more, since there's a broad spectrum of infection and only patients who were sick were tested, it's quite likely that there was even more transmission in the hospital.

Spreading in hospitals: So, like severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) -- other coronaviruses -- before it, the Wuhan coronavirus is spreading in hospitals.

The virus appears to be quite infectious.

Read more from Dr Frieden here.