With the winter fast approaching in the northern hemisphere we will probably see an increase in the number of swine flu infections.  Some of the terminology used in discussing this infection can be quite confusing  so here are some terms you may come across.

An infection is said to be Endemic in a population when  there is a constant amount of  infection present.  For example in the UK there will be a number of chicken pox cases reported each year.  The chicken pox is passed around from person to person but as long as the number infected remains more or less the same each year, then we can say that chicken pox is endemic in the population.

On the other hand if we take malaria as an example, we will find a number of cases detected each year in travelers returning from abroad.  The number may even be the same from year to year.  There is one significant difference however, and that is, that the infection cannot be passed on from person to person.  In the case of malaria we need the presence of an external factor for the disease to run through the population.  This factor is the malaria carrying mosquito and since this insect does not exist in the UK, the disease cannot become endemic.

The definition rests on the fact that the numbers infected each year remains substantially the same and that the disease is capable of passing from person to person.

An Epidemic occurs when new cases of infection exceed substantially what is normally expected in a population.  The epidemic could be restricted to a specific hub such as a school or a city or it could affect an entire country.  For an epidemic we need high levels of infection that eventually level out and fall back.

For a Pandemic to occur we need a completely new disease to emerge which can be transmitted globally.  The present swine flu pandemic is such a disease.

The problem with the use of these terms in is that they lead to emotional responses in the general public.  When we hear of an epidemic or pandemic we assume the worst.  The terms refer to numbers and transmission of infection but they do not describe the seriousness of any disease.  For example it is possible to have a pandemic of a very mild infection. So when we hear of epidemics or pandemics we need to look at the disease in question as well as the risk of infection .