A second worker involved in dealing with the bird flu outbreak on a farm in Suffolk, is being tested for the disease, health experts have announced.
Workers wearing protective clothing during the turkey cull
The Health Protection Agency said it would be known on Thursday if they were infected with the H5N1 virus.
A vet who became ill has already tested negative for bird flu and seasonal flu.
The HPA said other workers may develop similar symptoms, as it was the season for respiratory infections, but that it did not expect anyone to have H5N1.
The BBC's medical correspondent Fergus Walsh said it was understood the worker being tested was a Portuguese farm worker who had developed a cough and a fever who was being tested in hospital.
But he added it was believed there was no more reason to be concerned in this case than in that of the vet.
'Time of year'
In a statement, Dr Jonathan van Tam, a flu expert at the HPA, said: "We are not expecting any workers to test positive for avian flu as they have followed all the necessary precautions in terms of protective clothing, hygiene measures and have been offered antiviral drugs.
"We are however expecting to see a number of workers with symptoms caused by other non-flu respiratory viruses over the coming week as this is the time of year when we see an increase in these infections."
The HPA again stressed that H5N1 was predominantly a disease which affected birds and which does not transmit easily to humans.
There has been no evidence so far that the virus can pass easily from human to human.
So far, the H5N1 strain of bird flu has infected over 270 people across the world, mainly in South East Asia, and has killed over 160.
However, experts fear the virus could mutate at some point in the future and trigger a flu pandemic, potentially putting millions of human lives at risk.
Following the discovery of the virus on the Bernard Matthews poultry farm in Holton, almost 160,000 turkeys were killed.
A 3km (1.9 mile) protection zone and a 10km (6.2 mile) surveillance zone are in place around the Holton farm.
Poultry owners in a wider restricted zone, covering 2,090 sq km (807 sq miles) around Holton, have been told to keep their flocks isolated from wild birds.
Scene of outbreak
All poultry to be culled
Visitors disinfected and restricted access
3km Protection Zone
Poultry kept indoors and tested
10km Surveillance Zone
No movement of poultry to or from area except for slaughter
Trains carrying live poultry are prevented from stopping in the protection zone
Bird fairs and markets banned
Increased surveillance of wetland areas
Domestic birds not to share water used by wild birds
Footpath restrictions likely only on free-range farms
People in towns not affected unless they keep poultry.
Isolation of poultry from wild birds
Poultry movements to be licensed