A kitchen that prepared food for patients in Altnagelvin Hospital is now free of rats and has reopened, the Western Trust has said.
It was quickly shut down last week after vermin were spotted, and alternative arrangements were made for patients' meals.
The Western Trust said that the kitchen, which has a five star food hygiene rating, has been declared pest free and is back in operation.
Foyle DUP MLA Gary Middleton said: "The idea that any kind of vermin has been seen near the kitchen where patients' food is prepared is certainly alarming.
"But it is reassuring that the trust acted fast and appropriately as soon as it became aware that vermin had been seen.
"People should be reassured by the five star hygiene rating the trust has for this kitchen because these ratings are carefully awarded, and to reach this level of excellence is not easy."
The Western Trust confirmed to the Belfast Telegraph that the kitchen had been thoroughly inspected and declared fit for purpose by a pest control expert.
"The Western Trust took appropriate action to close the Ward 32 kitchen recently due to sighting of pests, with food/beverages services for patients being provided from an alternative kitchen," it said.
"There was minimum disruption to the food service for patients in the ward."
When there has been a reported sighting or suspected sightings of pests, the trust's pest control contractors are called out.
"The pest control specialists carry out treatments following each visit or call out as appropriate," the trust added.
"They also provide specialist advice to the trust following the contract visits, for example, in relation to minor repairs to the building, reviewing housekeeping/cleaning arrangements and monitoring.
"Proactive use of pest control systems is a sign of good hospital management and is well supported by the vigilance of staff to ensure that any pest control issues are dealt with quickly."
The trust said the Ward 32 kitchen is registered with the Environmental Health Department "and is regularly inspected as part of EHO visits".
"It would be unrealistic to expect that large, public buildings with a significant throughput of people will be completely pest-free. However, the public should be reassured that the trust has robust procedures to quickly and effectively deal with pests."