Thomas Cook agent Susan Cooper and her husband died of carbon monoxide poisoning after suddenly fell ill when staying in an Egyptian hotel room, a pathologist told an inquest.
However, experts could not be sure of the source of the poisonous gas that killed the couple, Blackburn Coroner’s Court heard.
The couple, from Burnley, Lancashire, died suddenly on August 21, 2018 after they became ill.
They were staying at the Steigenberger Aqua Magic Hotel in Hurghada.
A statement from a German tourist read at the inquest said there was a bedbug infestation in the room next door to the Coopers which was treated with a pesticide, referred to as Lambda, at lunchtime, with the Coopers falling ill in the early hours and dying the next day.
The two rooms had an adjoining door, but this was kept locked.
Home Office pathologist Dr Charles Wilson gave a cause of death for Mr Cooper as carbon monoxide toxicity and heart disease, and carbon monoxide toxicity for Mrs Cooper, there BBC reported..
Toxicology expert Professor Robert Chilcott told the hearing he detected the presence of carbon monoxide in blood samples from the bodies of the couple but he could not be certain of the levels.
He said the levels were sufficient to suggest “severe exposure” to carbon monoxide.
Chilcott suggested in less developed countries the pesticide Lambda is sometimes diluted with another substance, dichloromethane, which causes the body to metabolise or ingest carbon monoxide.
He added: “I would say a ten-hour exposure duration, in theory, would be sufficient to cause carbon monoxide poisoning.”
He also said there were occupational limits in the UK about how much you are able to inhale and spraying it, as in the hotel room, would “rapidly exceed” those exposure limits
Dr Nick Gent, a former senior medical adviser to Public Health England, said he agreed on the presence of carbon monoxide in the Coopers’ blood but had no idea about the source.
Kelly Ormerod, the Coopers’ daughter, had earlier described her parents as fit and healthy for their age and said they had been enjoying a “brilliant” holiday with her, their three grandchildren and family friends.
Mr Cooper, 69, a builder, and his 63-year-old wife, Susan, a bureau de change cashier at a Thomas Cook branch in Burnley, were found seriously ill in their room by their daughter after they failed to emerge for breakfast.
Her father was declared dead on the hotel room floor and his wife in hospital hours later.
The hearing was adjourned until Friday.