Transmission routes of the virus causing viral hemorrhagic fever: Extreme precautions are prudent but high-quality evidence must be gathered

To the Editor—Moon et al¹ reported that airborne precautions might be needed when dealing with fatal cases of severe fever with thrombocytopenia syndrome (SFTS). For diseases with high fatality rates that lack specific and effective treatment, it is prudent to take a more extreme prevention strategy than that based on the documented transmission route.² One example in which this strategy is applied is Ebola virus disease, for which extreme precautions are taken.³ Given that SFTS virus (SFTSV) is a viral hemorrhagic fever virus that causes severe disease with a high fatality rate, we apply the same strategy to SFTS. Airborne precautions are recommended when healthcare providers conduct aerosol-generating procedures such as endotracheal intubation on a patient suspected of having SFTSV.

The transmission route of the disease treated under this prevention strategy should also be carefully examined during each outbreak. To date, airborne transmission of naturally occurring hemorrhagic fever viruses has not been documented.² The patient in the Moon et al article was a doctor wearing only a fluid-shield mask and gloves who performed endotracheal intubation on an SFTS patient and was infected with SFTS thereafter. Respiratory droplets are thought to be generated during endotracheal intubation, and protection of the eyes, nose, and mouth is recommended during the procedure in accordance with standard precautions.² Because the doctor in the article did not protect his eyes, it was possible that he acquired SFTSV through droplet contact with his eyes during the intubation procedure. However, this observation does not provide any evidence that SFTSV infects people through airborne transmission.

It is crucial to improve the level of precautions taken in acute-care settings in SFTS-endemic areas to prevent SFTSV transmission because most of the nosocomial transmissions of SFTSV are thought to occur before the diagnosis of the patient (infector) is confirmed as SFTS by the laboratory.^4–9 Standard precautions should be the norm for clinicians when they treat patients suspected of having SFTS. Between April 2013, when SFTS was designated as a notifiable disease in Japan, and December 2018, ∼400 cases have been reported in Japan.¹⁰ SFTS occurred sporadically in most patients, who were thought to have been infected with SFTSV through a tick bite during outdoor activities or by direct contact with a sick animal. To date, no case of healthcare-associated infection has been reported in Japan. However, we need to remain conscious of the risk of healthcare-associated infections.

We believe that strict adherence to standard and contact precautions can reduce the risk of nosocomial transmission of SFTSV and that taking airborne precautions as an extreme measure is required during aerosol-generating procedures. Additional evidence on the route of SFTSV transmission might guide the best precautions in the future.