The untimely deaths of John Cooper and his wife Susan at the Steigenberger Aqua Magic Hotel in the resort of Hurghada, in Egypt, have shocked and stunned the local community.
The all-inclusive holiday had been booked through Thomas Cook, where Mrs Cooper was a "loyal and long-standing" member of staff.
The company has since removed other families from the hotel after "high levels of illness" were reported among other guests there.
A major investigation had been under way since John and Susan Cooper's deaths, however, Thomas Cook has now announced the investigation will be expanded.
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In a statement to the Burnley Express, a spokesman for Thomas Cook said: "We are aware that a number of customers have come forward to say they have experienced illness while staying at the Steigenberger Aqua Magic Hotel in Hurghada, Egypt.
"We are very sorry for any customers whose holidays have been spoiled. We take all illness very seriously and have taken the decision to expand our ongoing investigation into the sudden deaths of two of our customers at the Steigenberger earlier this week to include any other customer reports of illness at the hotel this summer. As part of this, we plan to contact every Thomas Cook customer that has returned from staying at the hotel in the last three days. We are also putting a dedicated team together to prioritise all complaints from this hotel."