By JULIE FITZGERALD
It's a serious, sometimes fatal, disease which most of us have suffered from at some time.
It's influenza, or flu, and it does the rounds every winter. Some years are worse than others, but up to 20 per cent of the population can be hit by flu.
Hospitalisation and mortality rates vary depending on the particular strain of virus prevalent in a given season.
New Zealand's worst flu epidemic in recent years was in 1996, when 94 people died. From 1990 to 1999, 307 people died from complications caused by the flu.
The bug leaves sufferers ill for up to 10 days, usually with a high fever and requiring bed rest. They have shivers and shakes, muscular aches, headaches, a cough, possible vomiting and, rarely, complications like pneumonia.
Although people often confuse the symptoms of flu with those of a bad cold, the symptoms of a cold are much milder, and last only two to four days.
The Ministry of Health reports that last year GPs were consulted 4079 times by people with flu-like illness. It estimates that 48,000 people suffered from the flu during the "season".
This represents a huge burden on the health system and in order to alleviate the suffering, the ministry offers a vaccine at the beginning of each winter.
It is available free to people over 65, and others whose health puts them at risk of complications from flu.
The vaccine takes 10 to 14 days to become effective, but studies suggest that it cuts admittances to hospital during the flu season by half and deaths by two-thirds for people aged 65 years and over.
Ministry virologist Lance Jennings has just returned from Geneva, where he helps the World Health Organisation fight influenza globally.
He said the flu vaccine had a significant cost-benefit to governments.
"There is a substantial and under-recognised burden of disease here in New Zealand and internationally."
But New Zealand could still do better to fight the problem, he said.
"We are up with most European countries and level with Australia but we are behind the United States and Canada."
Three types of virus cause influenza, known as A, B, and C.
Viruses A and B are thought to cause the worst epidemics of flu and are the ones people can be vaccinated against. Type C causes a mild respiratory illness and is not thought to be responsible for the serious epidemics. The viruses are also divided into sub-types.
The viruses are constantly changing, offering people little chance to gain immunity. As new strains appear, the body can succumb again, explaining how people get flu repeatedly over the years.
The latest strain to hit New Zealand, the B/Hong Kong virus, is not covered by this year's flu vaccine, but is relatively mild.
The World Health Organisation's Influenza Monitoring Centre does its best to keep ahead of the game, forecasting what strains of virus are likely to be prevalent in the coming season.
A flu vaccine contains three strains of flu virus, circulating globally each year. The viruses are grown in hens' eggs, then killed and purified before being made into a vaccine.
Some of the most serious global health events in recent history have been influenza pandemics.
The worst of all, the 1918 Spanish flu pandemic, killed up to 50 million people worldwide, or 2 per cent of the world's population at the time.
Last month, British scientists announced plans to exhume the body of a young woman who died in the 1918 pandemic in a bid to develop treatments for other strains of influenza.
A team from St Bartholomew's Hospital in London believes that the London grave of Phyllis Burn, 20, who died in October 1918, could still harbour the virus.
Burn was buried in a lead coffin within a brick vault, conditions that scientists believe would have preserved the body well enough for samples of the virus to be extracted.
If they find intact cells of the virus, they say they should be able to map its genetic structure and help to prevent a repeat of the pandemic.
Other serious pandemics included the 1957-58 Asian flu and 1968-1969 Hong Kong flu.
In 1997, there was an outbreak of avian flu in Hong Kong. Eighteen people were taken to hospital and six died from the virus, which had previously been seen only in birds.
Officials ordered the slaughter of all chickens, as the animals were known to be infected by the virus.
Studies showed that this type of flu spreads easily from poultry to people, but it is not spread very easily between people.
Hong Kong has since been hit by three major bird flu outbreaks.
And in a warning to the talkative, one professor claims that Hong Kong people are more likely to catch the flu because they talk too loudly, too often.
"When you talk too much and too loudly, you are traumatising your throat," said Thomas Chan, a professor at the department of medicine and therapeutics at Hong Kong's Chinese University.
Since the noise level in Hong Kong was relatively high, people tended to shout in order to be heard, he said.
Chan also said people who kept their mouths open longer increased the chance of the flu virus attacking the throat and airways.
So, next time you're having a lengthy gossip in a crowded pub, consider the health risks.
By JULIE FITZGERALD