Human-to-human transmission of a deadly tick virus has been reported for the first time in South Korea, health authorities said Wednesday, raising concerns over the potential spread of the disease.

Four medical staff in Seoul were confirmed to have been infected with the virus in September last year by a 68-year-old woman who was suffering from severe fever due to thrombocytopenia syndrome, or SFTS, a fatal disease contracted through tick bites.

Hospital sources suspect that the virus was transmitted while the staff were conducting cardiopulmonary resuscitation on the patient, officials said. She died of blood poisoning one day after she was hospitalized.

While all staff were quickly cured under treatment, one medial resident had to be hospitalized for a week with serious symptoms, they said.

This first case was belatedly reported to the Infectious Diseases Society of America, the health authorities said.

The syndrome, which causes fever, vomiting, diarrhea and multiple organ failure, has been found to have a fatality rate of around 10 percent. No direct vaccines have been created so far.

Korea has had a higher fatality rate from the tick-borne virus since 2013. Of 36 confirmed patients in 2013, 16 died from tick bites ― a fatality rate of 47.2 percent. From January to August last year, 10 of 24 patients died from the tick virus.

While SFTS fears gripped the country at the time, the health authorities had only warned of tick bites, not of secondary infection. Human-to-human transmission was thought to be nearly impossible.

Five cases of human-to-human transmission have been reported in China, with three cases involving intrafamily transmission, the authorities said.

Stern precautionary measures should be taken when a suspected case of the virus infection is reported since it can be transmitted through blood or respiratory secretions, experts said.

Doctors advised people to wear long clothes when spending time in the wild and to wash their clothing as soon as they return home.

By Lee Hyun-jeong (rene@heraldcorp.com)