Why is our rich and powerful society unable to prevent, defeat, or even contain the yearly onslaught of influenza? A clutch of papers in this issue provides glimpses of the answers.

What is commonly known as influenza or the flu is a syndrome, not a disease. Each year scores of different respiratory viruses (and a few bacteria) cause a mostly benign illness, which cannot be distinguished clinically by causal agent. The syndrome should be referred to as influenza-like illness rather than just influenza. Influenza should be reserved for the illness caused by influenza A or B viruses. Influenza-like illness gives a better idea of the difficulties in diagnosis. Useful pointers may be the seasonality of the epidemic (respiratory syncytial virus and influenza A and B are usually autumnal or winter epidemics) or the age group concerned (respiratory syncytial virus has an affinity for very young people). Another exception may be the presence of a pandemic or a local epidemic in which the causal agent has been identified. However, our knowledge of the annual microbiological breakdown …