Levels of Legionnaires' disease at a lab site linked to the foot-and-mouth outbreak in Surrey are "insignificant", the Institute for Animal Health says.
A 3km (1.8 mile) protection zone is in place around the affected farms
The Health Protection Agency (HPA) launched an inquiry into the IAH after a case of Legionella in a contractor.
The IAH's John Anderson said the amount of Legionnaires' found was so low it could be considered background level.
The foot-and-mouth investigation centres on the Pirbright site which also contains vaccine producer Merial.
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'.
Dr Anderson, the IAH's head of labs, said the Health and Safety Executive (HSE) collected samples from its site on 18 July.
He said he did not know where the allegations of Legionella contamination at the lab began, and that the story was a "regrettable distraction" from testing samples from the foot-and-mouth outbreak.
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 to 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 were still being awaited.
Legionnaires' disease is caused by a bacterium that causes flu-like symptoms if it is converted into aerosol form from water - for instance, in showers or spas - and then inhaled.
A European Union export ban on British meat and livestock will remain in place until at least 25 August 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 (Defra) said that 362 animals had 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.
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 the Institute for 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".
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.