Two people who recently worked on a poultry farm in the UK have tested positive for avian influenza (bird flu).

The UK’s Health Security Agency (UKHSA) said the detection of the two cases of avian influenza A (H5) came about following the introduction of an asymptomatic testing programme for people who have been in contact with infected birds.

The two people returning positive tests are known to have recently worked on an infected poultry farm in England.

Neither had experienced any symptoms of avian influenza and both have since tested negative in follow up tests.

The UKHSA says that detection of avian influenza in poultry workers can follow contamination of the nose and throat from breathing in material on the affected farm, or can be a true infection. It can be difficult to distinguish these in people who have no symptoms.

In these two cases specifically, one individual is likely to have had contamination of the nose and/or throat from material inhaled on the farm, while for the second individual it is more difficult to determine which is the case.

Contact tracing is underway in the case of the second individual.

The UKHSA said that it has not detected evidence of human-to-human transmission and these detections do not change the level of risk to human health, which remains very low to the general population.

Prof. Susan Hopkins, chief medical advisor to the UKHSA, said: “Current evidence suggests that the avian influenza viruses we’re seeing circulating in birds around the world do not spread easily to people.

“However, we know already that the virus can spread people following close contact with infected birds.

“Globally, there is no evidence of spread of this strain from person to person, but we know that viruses evolve all the time and we remain vigilant for any evidence of changing risk to the population,” Prof. Hopkins added.

In the asymptomatic surveillance programme, poultry workers are asked to take swabs of their nose and throat which are tested for the presence of the virus, during the 10 days after their exposure.

They may also be asked to have a finger-prick blood test to see if antibodies against bird flu can be detected.

The UKHSA follows up on all individuals who have been in contact with confirmed human cases of bird flu, with testing and antivirals offered for those with the highest risk exposure.