Doctors across Northern Ireland have been sent letters to distribute to more than 40,000 patients considered to be at "at risk of severe illness" if they contract coronavirus.
The letters advise the patients to stay at home and avoid all face to face contact for at least 12 weeks, except for carers and healthcare workers.
A template letter has been sent by the Northern Ireland Health and Social Care Board to all GPs.
Doctors are being asked to forward the letters to patients they believe are particularly vulnerable and at risk.
The letter opens with a stark warning: "We have identified that you, or the person you care for, is at risk of severe illness if you catch Coronavirus (also known as Covid-19)".
It adds: "You are receiving this letter because you, or someone you care for, has an underlying disease or health condition. This means if you catch the virus, you are more likely to be admitted to hospital than others.
"The safest course of action is for you to stay at home at all times and avoid all face-to-face contact for at least twelve weeks from today, except from carers and healthcare workers who you must see as part of your medical care."
The patients are told that if, at any point, they think they have developed symptoms of coronavirus, such as a new, continuous cough and/or high temperature, they should call the NHS 111 NI helpline "as soon as you get symptoms."
They are advised not to attend any gatherings in private places, including family homes, weddings and religious services.
The letters also contain guidance on how patients should interact with others in their household.
- Minimising time spent with others in enclosed spaces and keeping shared spaces well ventilated
- Keeping 2 metres away from others and encouraging them to sleep in a different bed where possible
- Using separate towels and, if possible, a separate bathroom
- Avoiding using the kitchen when others are present and to take their meals to their own room to eat if possible.
The patients are also told to arrange for a friend, neighbour or family member to collect any prescriptions they need from a pharmacy as they should not go in person.
They are also advised to prepare for hospital treatment if they contract Covid-19.
"To help us provide you with the best care if you need to go to hospital as a result of catching coronavirus, we ask that you prepare a single hospital bag," the letter says.
"This should include your emergency contact, a list of the medications you take (including dose and frequency), any information on your planned care appointments and things you would need for an overnight stay (snacks, pyjamas, toothbrush, medication etc)"
There is also advice on how to help their physical and mental wellbeing during their time in isolation.
The template letters have been sent to GPs and will be forwarded to patients during the coming days.