A probe into a reported Legionnaires' disease case at the Pirbright lab site linked to the Surrey foot-and-mouth outbreak is being carried out.
A 3km (1.8 mile) protection zone is in place around the affected farms
The Health Protection Agency (HPA) said the probe related to the Institute for Animal Health (IAH) on the site.
IAH head of labs John Anderson said HPA results showed levels of Legionnaires' found were "insignificant".
He said the amounts could be considered background levels, and that the story was a "regrettable distraction".
Health inspectors are reportedly looking into the possibility that foot-and-mouth disease was originally transferred by employees at vaccine manufacturer Merial, also based at the Pirbright site.
Dr Anderson said the Health and Safety Executive (HSE) collected samples from the Pirbright site on 18 July following a case of Legionella in a contractor.
The Health and Safety Executive has said there is a "strong probability" that the recent foot-and-mouth outbreak began at Pirbright.
But the HPA said there is no link between foot-and-mouth and Legionnaires'.
IAH director Martin Shirley said there was no evidence of a failure of biosecurity at its lab.
Prof Shirley said all foot-and-mouth virus was destroyed before it left its site, and even if that failed an effluent chemical treatment facility would kill the disease.
He said the amount of the virus used in vaccine production by Merial was one million times greater that used by the institute.
It is thought that the Legionnaires' case pre-dates the outbreak of foot-and-mouth.
A statement from the HPA said its early findings indicated that an individual linked with Legionnaires' had been working at the ISO10 building on the Pirbright site.
"These findings, backed up by temperature monitoring in the same area, suggested that the Institute was carrying out all necessary maintenance and monitoring work in compliance with the Approved Code of Practice for the control of Legionella," it continued.
Investigators were examining where the patient had visited in the 10-14 days prior to falling ill, including their home, workplace and anywhere else they may have travelled to.
The statement added that results of tests carried out on further samples are still being awaited.
Legionnaires' disease is caused by a bacterium that causes flu-like symptoms if it is converted into aerosol form from a water - for instance, in showers or spas - and then inhaled.
A European Union export ban on British meat and livestock remains in place following the discovery of foot-and-mouth disease at a Surrey farm on 3 August.
A spokesperson for the Department for Environment, Food and Rural Affairs said that 362 animals have been culled at a third farm, which is next to the second infected farm, on suspicion that the disease could be developing there.
This brings the total number of animals culled so far to 576.
The Conservative MP for the area, Humphrey Malins, said he was impressed by the quick response to events.
He said: "The government are following the best scientific advice that they can get and I have no particular reason to quarrel with that.
"This is a case where the government have learned lessons from 2001. They've reacted very quickly indeed on this."
The first cases of foot-and-mouth were found in cattle at Woolford Farm, near Guildford, on Friday and a second outbreak was confirmed at a farm on Monday. Cattle in both cases have been culled.
Restrictions on taking animals to abattoirs have been lifted, but many movements of livestock - such as sending animals to market - are still banned.
Some restrictions had already been lifted in Scotland and Wales.
Both Merial and Institute of Animal Health had been using the strain of the virus, but the HSE did not specify which of the two was to blame.
It is understood, however, that investigations have discovered a link between problems with drainage and the possible actions, accidental or deliberate, of Merial employees who may use nearby allotments.
Merial said it had conducted "intensive internal investigations" and had "complete confidence" in its processes and procedures.
It confirmed one of its employees had accompanied investigators to an allotment but said there was "no evidence linking this member of staff to the outbreak".
At a meeting in Brussels, EU veterinary and food safety experts decided emergency measures banning all British exports of meat, milk products and live animals would remain in place until 25 August.
The committee will meet again on 23 August.
Prime Minister Gordon Brown chaired another meeting of the Cobra emergency committee on Wednesday evening to discuss the outbreak.
Following criticism from some farmers and opposition parties, all footpaths within the 3km (1.8 mile) protection zones around the affected farms in Surrey have been closed.
A 10km (6.2 miles) surveillance zone is also in place.