Figure 1. Consultation rate (per 100,000 population) for influenzalike illnesses with sentinel physicians in England in 1988–2002 (from the Royal College of General Practitioners Weekly Returns Service). Baseline activity is defined by a consultation rate <50/100,000; normal seasonal activity, 50–200/100,000; higher than seasonal activity, 200–400/100,000, and epidemic activity is defined as >400/100,000 population.
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