A member of the Air Corps has tested positive for Covid-19.
The man is in a serious but stable condition in an intensive care unit in the border region.
A number of his colleagues in the same wing as him have been forced to self-isolate.
His positive test follows the return from Italy of a number of Air Corps staff.
Although serious, his condition has improved slightly in the past 48 hours, according to Defence Force sources.
They said: “The man is not a pilot but he has contact with them and other personnel.
“He was at work until only a few days ago. Some of his colleagues came back from northern Italy recently.”
It is understood that after the Italian trip, two members of the Air Corps put themselves into self-isolation.
They have since been tested and found to be negative.
The Defence Forces press office declined to comment as it does not comment on individual staff matters.
The presence of the virus could potentially be a big blow to the short-staffed Irish Air Corps in general but to the Emergency Aeromedical Service (EAS) in particular.
Due to staff cuts the service had to cut back on some of the cover it provides the National Ambulance Service.
Instead, members of the Irish Coast Guard have had to be tasked to fill in for them, as have the cash-strapped Irish Community Rapid Response charity air ambulance.
Indeed, so short-staffed is the Air Corps that senior officers have been drafted back from their management positions to fly the EAS.
They have also been drafted in to fly Garda helicopters.
Last November, due to what the Air Corps described as “HR challenges”, the service announced it couldn’t operate its EAS for four days per month for a period of four months until February 2020.
It said at the time that this interruption was “regrettable but necessary” from a safety and governance perspective.
Its “HR challenges” are well-documented and include, in particular, the recruitment and retention of pilots.
This story has been amended