Shinji Shimada, the president of the University of Yamanashi, right, announces that a baby girl is infected with the coronavirus at a news conference at the university's hospital in Chuo, Yamanashi Prefecture, on April 1. (Katsumi Mitsugi)

A baby girl under the age of 1 is infected with the new coronavirus in Yamanashi Prefecture and in serious condition in a hospital, local government authorities announced April 1.

The girl's parents, who tested negative for the virus the same day, rushed her to a hospital on March 31 after she stopped breathing at home.

Doctors at the University of Yamanashi Hospital revived her but found she was infected with the virus after they administered a polymerase chain reaction (PCR) test.

The girl is in the hospital's intensive care unit where she is undergoing treatment.

Initially the hospital did not assume that she was infected with the virus, so the medical staff were not prepared well to protect themselves from the virus.

The hospital instructed 44 medical staff, including doctors thought to have had close contact with the girl, to quarantine themselves at home for two weeks. The hospital also said 12 patients are being monitored for symptoms of the virus.

Doctors do not know why the girl stopped breathing but suspect it had little to do with the coronavirus since she has only light symptoms of the pneumonia-like disease.

The girl was given a CT scan of her chest after she arrived at the hospital. The results indicated she had pneumonia, leading doctors to test her for the coronavirus.

She underwent two PCR tests. Both were positive.

The diagnosis came as a shock to her parents since neither have any coronavirus symptoms, such as a cold, and were unable to explain how she contracted it.

The Yamanashi prefectural government is investigating how the girl got the virus and is attempting to trace all persons who had recent contact with her to identify its transmission route.