Although HIV is regarded as a progressive disease, some patients can remain asymptomatic and may have no shortening of their lifespan or have to take drugs, writes Eoin Burke-Kennedy.
John believes he would not know he has HIV if he had not been tested six years ago. "As of this point I am completely asymptomatic. I don't require any medical treatment."
John - who is 52 and living in Dublin - is what doctors call a long-term non-progressive HIV patient.
Although HIV infection is associated with progressive disease in the majority of cases, the rate at which patients advance to Aids-related illness can vary.
It has long been observed that a small percentage of those with HIV appear to remain symptom-free in the absence of treatment for long periods - in some cases, more than 20 years.
John is classified as a non-progressor because his CD4 cell count - a standard measure of the body's immune function - has shown little or no diminution since his diagnosis.
Most HIV patients can expect their CD4 cell count to fall by around 100 cells a year even in the absence of illness.
John says he has been told by doctors his condition probably won't effect the length of his life and that he may never have to go on drugs.
"Of course I worry when I get a head cold that maybe this is the start of something else but at this stage, luckily, my immune system is sufficiently strong."
Depending on the study, long-term non-progressors (LTNPs) are estimated to represent anywhere between 5 and 10 per cent of the HIV population.
But some experts question the validity of the term long-term non-progressive, arguing that most patients do eventually succumb to the virus and it is more a case of slow progression rather than non-progression.
In addition, since HIV has only existed for around 30 years and because LTNPs only represent a small minority of cases, it may be impossible at this stage to accurately assess the long-term effects of the virus.
Nevertheless, a number of studies have attempted to better understand the immunological response of these patients to the virus in the hope that it might lead to improved HIV treatment through the manipulation of the immune system.
Dr Derek Freedman, a specialist in genito-urinary medicine and a consultant at St James's Hospital's sexually transmitted infection (STI) clinic, explains that in any biological situation there are always going to be some people who progress much slower.
"The reasons for this are often multi-factorial," he says. "There can be discrete differences between various clades or strains of the virus. For instance, it has been well described that HIV-2 progresses more slowly and less destructively than HIV-1."
Another factor, Freedman says, is the amount of the virus the host is initially exposed to. "The more virus you get inoculated the first time, the more likely you are to get an acute infection that would progress more rapidly."
Moreover, some people - for genetic reasons - have fewer receptors in their immune cells for the virus to latch onto and this can mean the virus is not taken up in the same quantity or as rapidly.
The progression of the virus is also related to the general function of the immune system.
"So people who get it at a younger age progress more slowly because they are starting off from a stronger base of their immune system.
"Equally, people who get it when they are older tend to progress more rapidly because their immune system has been diminished with age anyway."
There are also extraneous factors, such as smoking cigarettes, says Freedman. "Cigarettes damage the immune system. People who smoke are going to go down quicker. So there is a complex inter-relationship between all these factors."
A US study - published in the Aids journal last year - argued that nowhere in the various definitions of what constitutes a LTNP was the host's viral load considered. The viral load refers to the amount of HIV in a person's blood, usually measured by a test that determines the number of copies of HIV in one millilitre of blood.
The study found that a percentage of the LTNP group had undetectable HIV-1 viral loads and some patients had even been told they did not have HIV after the viral load testing was negative.
It concluded that these patients were demonstrating a natural ability to suppress virus replication in the absence of therapy.
Although the study admitted it was too early to postulate on the factors involved, it said "natural viral suppressors" represented one "unique extreme of HIV-infected patients".
"Even the longest long-term non-progressor will eventually witness a deterioration in their immune system," says Dr Jack Lambert, infectious diseases consultant at the Mater hospital.
"However, we can learn a lot from these individuals in terms of what are the components of the immune system which control infection and disease progression," says Lambert.
"But because they still become infected, studying these people might not give us the answer to developing a vaccine as the immune requirement for preventing infection may be different than what we are finding in these people.
"It is still a mystery as to why some people who have sex all the time with people who are HIV positive don't develop the infection," says Lambert.
Research is currently being carried out on a group of prostitutes in Nairobi, Kenya that for some reason have not developed the HIV infection, despite repeated exposure.
"When you're well and healthy you don't think about it all the time. I don't wake up every morning thinking I'm HIV positive," says John. "But I know its not going to go away and it does infringe on my life in terms of personal relationships. I suppose it's a comfort to know that it's long term."