After seven confirmed cases of coronavirus, all passengers who were on a flight from Zante to Cardiff have been ordered to self-isolate.
Passengers who were on TUI flight 6215 on Tuesday are now being considered as “close contacts” of those who tested positive for COVID-19.
The seven cases were from three different parties on board the flight from the Greek party island, which is also called Zakynthos.
Dr Giri Shankar, Public Health Wales director, said: “These passengers will be contacted shortly, but meanwhile, they must self-isolate at home as they may become infectious, even without developing symptoms. Anyone with symptoms should book a test without delay.
“Our investigations into a number of cases of coronavirus have indicated that a lack of social distancing, in particular by a minority of the 20-30 year age group, has resulted in the spread of the virus to other groups of people.”
He appealed to young people specifically to remember that “even if they feel they would not be badly affected by COVID-19” if they were to test positive, the virus could be “extremely serious, even fatal” if they passed it on to older or more vulnerable family members, friends or colleagues.
Dr Shankar added that although Wales has a low infection rate, “coronavirus has not gone away”. He reminded people over the bank holiday weekend of the importance of social distancing.
Greece is not on the list of countries travellers have to self-isolate for two weeks on their return to the UK.
The country’s case rate has risen recently, with 11.73 cases per 100,000 people in the week 8-14 August, compared with 14.89 cases per 100,000 people from 22-28 August, according to data from the European Centre of Disease Prevention and Control.
Countries with 20 cases per 100,000 people, or those nearing that, will be considered for the quarantine list, Health Secretary Matt Hancock has said.
There has been a “number of small clusters” of COVID-19 cases in Cardiff that are not related to the TUI flight, Public Health Wales said.
In north Wales, customers of the North and South Wales Bank pub in Wrexham between 9-20 August have been told to remain vigilant for symptoms of COVID-19 after staff members tested positive.