Influenza is a descriptive term for respiratory epidemic disease presenting with cough and fever. Influenza viruses are probably the most important of the pathogens that cause this condition. Clinical influenza occurs almost every winter in England and Wales and the outbreaks last 8-10 weeks. In recent years, influenza B virus outbreaks have occurred in January and February, whereas influenza H3N2 virus outbreaks have generally started long before Christmas. Influenza H3N2 virus outbreaks pressurize health service resources in winter more than influenza B viruses, that do not have the same impact in elderly people. Infections with influenza H1N1 viruses are also usually less severe in their impact than those with influenza H3N2 viruses, but, unlike influenza B viruses, influenza H1N1 viruses have a pandemic potential along with influenza H3N2 viruses. A diagnosis of respiratory infection in primary care is based on the presenting symptoms set,within the context of the current pattern of consultations of patients with similar illness. Measurement of temperature, inspection of the throat and examination of the chest or ears add a little to the diagnostic process, but in general these procedures do not help in identifying the organism. However, if it is known that influenza viruses are circulating in the community, the probability of influenza as the cause is greatly increased, as was shown in clinical trials of neuraminidase antivirals. Maximum confusion occurs when respiratory syncytial virus (RSV) and influenza co-circulate. Although RSV infection can occur throughout the winter in young children, it assumes more of an epidemic character just before Christmas in children and possibly in adults just after. During seven of the last 20 winters, influenza has been prevalent around Christmas/New Year. In routine virological surveillance or influenza-like illness in the community during the winters of 1997, 1998 and 1999, ca. 30% of swab specimens yielded influenza viruses and 20% RSV Given the limitations for routine surveillance, including variations in the interval between illness onset and specimen capture, the quality of swab, delays in transport, the growth properties of virus culture methods, etc., these figures probably underestimate the impact of both viruses in the community. The impact of influenza is considered against the background of total respiratory infections presenting to general practitioners over the last 10 years and some comparisons are made with the 1969 pandemic experience. Lessons relevant to pandemic planning are drawn. Current options for investigation and treatment are compared with those available in 1969. These include near-patient tests for assisting with diagnosis, widespread use of vaccination as a preventive in patients at increased risk, the availability of amantadine and the newer neuraminidase inhibitor antivirals and changes in the delivery of health care. Major advances in the understanding of influenza and improvements in investigation and treatment have taken place over the last 30 years. However, there are many obstacles before these can be translated into effective management of influenza sufferers and control of major epidemics.
