A new study shows that tropical and subtropical countries suffer far more illness and death during flu outbreaks than previously imagined, with both hospital admissions and deaths rising considerably during a flu outbreak.
Most strains of influenza are successfully fought off by the vast majority of people, who are back to normal within a week or two. Nevertheless, flu can cause serious illness, and sometimes death, in the elderly and other vulnerable people. A flu outbreak also puts a considerable strain on hospitals, as the number of people admitted always increases during an outbreak, not just for respiratory problems but for a variety of other medical conditions.
In cooler ('temperate') countries, all this has been known-backed up by a number of statistical studies-for many years. However, it has been assumed that flu is only a minor problem for people in the warmer parts of the world - the tropics and subtropics. Most countries in these regions are developing nations, and collecting and analysing data on flu and its complications is not easy. Flu outbreaks also happen at unpredictable and irregular intervals, in contrast to the seasonal pattern seen in temperate countries, and this creates problems for the statisticians.
Researchers in Hong Kong (which is in the subtropics) realised that they were well placed to study the impact of flu in such a location. Hong Kong has a sophisticated health care system, which includes advanced computerised record keeping. Ninety-five per cent of people admitted to hospital are treated in public hospitals and their records were available to the researchers. They developed new statistical methods to allow for the irregular nature of Hong Kong's flu outbreaks.