Public health experts are raising the alarm after a rise in reported cases of Norovirus.
Betsi Cadwaladr University Health Board and NHS Wales are warning anyone experiencing symptoms of the winter vomiting bug to steer clear of hospitals and GP surgeries.
Experts are warning you are most infectious in the 48 hours after symptoms have stopped.
The health board said it expected to see an increase in cases of vomiting and diarrhoea during the winter months as temperatures drop.
But after an outbreak last month closed multiple schools across the region, health experts have now issued a warning to try to combat the spread of the virus.
Gel hand sanitizer will not kill the virus, and experts encourage frequent hand washing, sticking with soap and water.
"The support of people across North Wales is absolutely vital in helping to reduce the spread of these viruses and others in our hospitals and wider communities.
"While most people will get over a case of Norovirus, for example, within a few days with rest and rehydration, it can be much more serious for people who are already ill, the very young and the elderly.
"Because Norovirus, like most viruses, may spread rapidly from person to person, our advice is to stay at home until you're feeling better.
"Even if your symptoms have stopped, you may still be able to spread the virus for the following 48 hours"
Symptoms of Norovirus include nausea, diarrhoea, vomiting, fever, headaches and aching arms and legs.
Symptoms usually start within one or two days of infection, but you should begin to feel better in a few days.