An NHS trust has accused the Tory Party of misrepresenting information after it was listed as one of the worst 50 hospitals for infestations.
The Conservatives said 70% of trusts brought in pest controllers at least 50 times from January 2006 to March 2008.
But Bromley Hospitals in south-east London said this was misleading as they were contracted to visit regularly.
The Conservative Party said the trust failed to provide researchers with more detailed information.
'Out of context'
The party got the data via a Freedom of Information Act request, with every hospital asked to reveal how often pest controllers had visited over the two-year period in question.
More than 1,000 incidents and five other trusts passed the 800 mark. All the respondents had reported some pest problem in the two-year period.
We want the Conservative Party to put out accurate information as this has caused unnecessary worry and concern for patients
Carol Holland, trust spokeswoman
But Bromley NHS Trust contacted the opposition party saying the information had been taken "out of context".
It said it had a contract with a pest controller which come out to its two hospitals every two weeks and visited its administrative building once a month.
Carol Holland, a spokesman for the trust, said: "We have only had to call out the pest controllers three times. One for a beetle infestation, once to remove a dead pigeon external to the building and once to remove a pigeon nest."
She added: "We want the Conservative Party to put out accurate information as this has caused unnecessary worry and concern for patients."
A spokeswoman for the Tories said: "We completely agree that regular preventative inspections are a good idea, in our table we simply recorded that according to the Bromley Hospitals NHS Trust's own figures, pest controllers have been called in 74 times.
"Unfortunately they did not provide us with examples of where and when infestations took place and we were therefore unable to corroborate that against the number of visits by pest controllers."