"The doctor sent me off for an X-ray which confirmed I had developed pneumonia," he says. As if this weren't bad enough, the real shock came with the results of a blood analysis which showed what was responsible for his ill health: pigeons.
"I have no connection with birds of any kind, apart from looking at them in the garden and being aware of pigeons in the city centre near the surgery. It was and still is an absolute mystery to me," he says.
Virologists had found that Dr Irons, who works in Cambridge, had fallen victim to a chlamydia infection, probably acquired from pigeons, making him one of an increasing number of victims of diseases caught from wild birds.
The whole issue of infections being passed from birds to humans is now to be investigated by a team of academics following an initiative by biologists at the University of Wales, Cardiff. Some estimates suggest that cases in Britain have doubled in the last five years as a result of an expanding urban bird population. Up to half the individuals of some species may be carriers of infection.
It is thought that even these figures may mask the real size of the problem. Many cases go undiagnosed because the symptoms are not severe, and because they are not given the blood tests that would confirm the presence of the disease. Instead, they are often treated for non-specific viral infections.
"There is poor public awareness about the risks, and we need people to be more vigilant," says Dr Tim Wreghitt, consultant virologist at the Public Health Service Laboratories, Addenbrooke's Hospital, Cambridge, who is an international expert on chlamydia infections.
Chlamydia psittaci, considered to be the most important of the family of infections, causes a respiratory infection in humans which in extreme cases can be fatal. One 60-year-old woman died of an infection she acquired from a dead pigeon which her cat had brought in. It's thought that she had probably breathed in contaminated dust from the carcase.
"The symptoms vary from the very mild to fatal pneumonia. Sometimes it can cause a neurological condition, sometimes a kind of paralysis, sometimes temporal arthritis with severe headaches. Many cases never get diagnosed because no one thinks of it. The crucial message is that if people have contact with birds and they get a respiratory infection they must tell their GP," says Dr Wreghitt.
The irony for those who suffer needlessly is that when the infection is diagnosed, by a blood sample, it is easily dealt with by antibiotics. Like many people who become infected, Dr Irons had no idea that birds had caused his ill-health.
"I have no recollection of any incident involving birds at all, but obviously I must have breathed something in at some time. It was very unpleasant and I was quite ill for about four weeks. I can't say I take any precautions now because it is impossible to make any changes to protect against something like this. It could happen at any time to anyone."
The infection is carried by birds in their guts and once they have it, they never lose it, though they are not necessarily ill themselves. It is usually passed on to humans when the contaminated and dried faeces are breathed in as dust. Unlike most bugs, the infective agent can exist for a long time in dried debris and simply breathing it in can cause an infection.
Only the slightest of contact is needed and patients have been known to become ill after coming into contact with a bird's nest while painting the house or after clearing an old attic. One fireman contracted a serious infection while searching a derelict house after there had been a fire next door.
Research by microbiologists in Australia has found that even cutting the lawn can throw up sufficient infected dust to cause the disease. People who feed pigeons in public places are also a group at risk.
The increase in cases is blamed on a growing urban bird population, thought to be a consequence of the greater availability of food in towns and cities.
"People feed more birds now, and over the last 20 to 30 years there has been an enormous spread of fast-food outlets whose customers often don't eat all their food, and throw it on the ground.
"There is also more litter and spillage about now because restaurants put their waste in black polythene sacks, which are easily broken, letting the birds get at the food," says Professor Chris Feare, who runs WildWings, a bird management consultancy.
There is a theory, too, that recent warm winters have allowed more diseased birds to survive, increasing the likelihood of contact with human beings, and of infection being passed.
Some believe that the solution lies in reducing urban bird populations by persuading people not to feed them. The tactic has worked in Basle, in Switzerland, but the chances of success of such a policy in Britain, one of the few countries where people buy food for wild birds, are thought to be slim.