HL Deb 24 January 2000 vol 608 cc173-4WA
Earl Howe

asked Her Majesty's Government:

What is the officially accepted definition of an epidemic. [HL559]

Lord Hunt of Kings Heath

The epidemiological definition of an epidemic is an increase in the frequency of occurrence of a disease in a population above its baseline level for a specified period of time. The term epidemic can be used when describing the pattern of either infectious or chronic diseases in the population.

Administrative definitions can be set for different diseases in which an arbitrary threshold is selected above which the term "epidemic" is applied. In the case of influenza, the Department of Health introduced in 1996 an administrative definition of an "epidemic" for a rate of consultation (with a sample of general practices) of 400 per 100,000 population in a week.

Such influenza activity in England is thus monitored through the Royal College of General Practitioners (RCGP) sentinel surveillance scheme. This records the number of first visits to a general practitioner with influenza-illness. Other respiratory illnesses prevalent at this time of year are recorded separately.

This system does not and cannot measure the real incidence of influenza, since it is restricted to those people who visit their general practitioner. In the present winter, the GP consultations avoided by patients consulting their pharmacists, using NHS Direct or self-medicating (as a result of special campaigns) are thought to have led to a substantial hidden element to the epidemic not revealed by the official figures. The serious nature of the illness amongst elderly people (reflected in the rates of acute bronchitis) and usage of hospitals reinforces the reality of the assessment of the severity of this winter's epidemic.

The severity of the disease itself can also vary from year to year. This year the elderly have been particularly affected by the complications of influenza. The level of cases of acute bronchitis, a serious complication of influenza, is the highest the RCGP surveillance system has seen for 15 years. In describing epidemics, some other countries formally include measures of severity in the definition of an epidemic. For example, the United States declares an epidemic when the proportion of deaths due to pneumonia and influenza passes a certain threshold.

The department has not introduced administrative definitions of an epidemic for diseases other than influenza.