UK hospitals are frequently plagued by pests including rats, fleas and cockroaches on wards and even in operating theatres, a report said on Wednesday.

NHS Trusts in England were forced to call out pest controllers to nearly 20,000 infestations during the past two years, figures obtained by the Conservatives under the Freedom of Information Act show.

Rats were found in maternity units while one patient woke to find maggots in her slippers, the report revealed.

About 80 percent of NHS Trusts reported problems with ants, 66 percent with rats and 77 percent with mice.

There were also incidents of cockroaches, biting insects or fleas and bed bugs and maggots.

Virtually all of the 127 NHS Trusts which responded had reported some problem with pests between January 2006 and March this year, with some reporting more than 800 incidents.

The worst was the fourth-largest trust in England, Nottingham University Hospitals NHS Trust, which passed the 1,000 mark.

The majority of infestations were in non-clinical areas, but about 20 trusts had to deal with problems including a small number of wasps in neo-natal units and operating theatres, flying ants on the main wards and mice on wards and in stores containing sterile materials.

The Tories said small insects, in particular, carry infections.

But the Department of Health insisted the case was unproven: "The Healthcare Commission have confirmed that health concerns around pest control have, to date, been negligible," it said in a statement.

"The claim that insects spread hospital-acquired infections is entirely unproven. There is no evidence of their carriage of antibiotic-resistant bacteria being a hazard to patients."

Clive Boase of the British Pest Control Association said it was not surprising hospitals, which are often the size of a small town, had to tackle pest infestations from time to time.

"Hospital sites are particularly at-risk locations," he told BBC radio. "They are large, busy sites."

Andrew Lansley, shadow health secretary, said the survey showed the disparity in hospital pest problems, but blamed the government for its four billion pound backlog in hospital maintenance.

He called for transparency in infection control, with the publication of figures nationally.

Ivan Lewis, a Department of Health minister, said the government did not deny there was an issue of pest control, but added cleanliness was a top priority for NHS trusts.

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