Abstract

Outbreaks of influenza have been recognised since ancient times and are responsible for devastating global morbidity and mortality. The characteristic epidemiological features of influenza include the occurrence of frequent, but unpredictable epidemics and periodic worldwide pandemics. Four pandemics have been recorded this century (table I). The potential consequences of a future pandemic can be judged by the impact of the 1918-19 pandemic, which was known as Spanish flu. Over a period of months influenza caused more deaths than the first world war. An estimated 200000 people died as a result of influenza in England and Wales alone, with over 20 million deaths worldwide. Influenza remains a great challenge to modern medicine. In this review I will discuss the epidemiology and surveillance of influenza outbreaks and recent advances in the diagnosis and management of infection.

Pandemics are caused by antigenic shift of influenza A resulting in the appearance of an influenza virus with a novel haemagglutinin (H antigen) or neuraminidase (N antigen) subtype. Influenza pandemics usually arise in China and spread westward to the rest of Asia, Europe, and America. Influenza viruses have been isolated from many different animal species, and recent evidence suggests that antigenic shift results from genetic reassortment of virus between humans and the animal reservoir. This process is facilitated by farming practices in south east Asia, which allow close proximity between humans, ducks, and domestic pigs.1

During interpandemic periods outbreaks of influenza A or B infection are reported nearly every winter and vary in severity. Antigenic variability during interpandemic …