Background: In routine practice, influenza is diagnosed on clinical grounds. When influenza is known to be circulating locally, this is usually accurate, but awareness of the markers of influenza severity could be used by physicians to aid diagnosis and begin appropriate treatment early. This analysis compared baseline symptom profiles of subjects with severe and non-severe influenza. Methods: Symptoms of influenza-like illness (ILI) were recorded from 2235 subjects in six clinical trials of inhaled zanamivir 10 mg bd. ILI was defined as fever (37.8 degreesC) or feverishness plus at least two of the following: headache, myalgia, cough, sore threat, weakness, nasal congestion, loss of appetite. Results: Thirty percent (474/1572) of influenza-positive subjects were classified as having severe influenza and had a higher mean baseline temperature of 38.5 vs. 38.1 degreesC (P < 0.001) Symptom profiles were similar in severe and non-severe groups; severe subjects had higher symptom scores but did not consult their physician earlier than non-severe. Zanamivir reduced the time to alleviation by 3 days (8 vs. 5 days, P < 0.001) in severe subjects and by 1 day (5.5 vs. 4.5 days, P < 0.001) in non-severe subjects. In severe subjects > 50 years old, zanamivir reduced the time to alleviation by 7 days (11.5 vs. 4.5 days, P = 0.004) compared with 2 days in severe subjects < 50 years (7.5 vs. 5.5 days, P < 0.001). Conclusions: Symptom profiles of subjects with severe and non-severe influenza were broadly similar; baseline temperature and total symptom scores were markers of severity. Time to alleviation was variable in untreated patients, but was reduced with zanamivir to between 4.5 and 5.5 days regardless of age or severity of illness. (C) 2001 Elsevier Science B.V. All rights reserved.
