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When I sat my final M.B. written exams one of the questions was, “Discuss the uses and abuses of the word influenza”. I didn't know then what the examiners were getting at and I still don't now although I know considerably more about influenza than I did then.
Clinical `influenza' (or influenza-like illness) may be caused by influenza viruses A and B, respiratory syncytial viruses (RSVs) A and B and probably other viruses including the newly identified human metapneumovirus (see Lucina page 386). Although paediatricians are familiar with RSV because of bronchiolitis it is, in fact, responsible for many influenza-like illnesses in children and adults.
During the winters of 1995–96, `96–97, and `97–98 a virological study (MC Zambon and colleagues. Lancet 2001;358:1410–6, see also editorial, ibid: 1382–3) was carried out in 10–15 general practices across England and Wales. Nasopharyngeal swabs were collected from people with an influenza-like illness (loosely defined) and examined for influenza virus and RSV by tissue culture and multiplex reverse transcription PCR. Seven hundred and sixty-two of the 2226 patients tested were children under the age of 14. In the three successive winters 32%, 33%, and 21% of the children under 5 years and 49%, 38%, and 41% of the children aged 5–14 years tested positive for influenza viruses. During the same winters 20%, 37%, and 41% of the under 5s and 7%, 22%, and 17% of the 5–14 year olds tested positive for RSV. In all three winters RSV was the predominant virus in infants.
Influenza and RSV outbreaks occur at about the same time in probably half of winters and they may be clinically indistinguishable. New virus-specific drug treatments and the development of an effective RSV vaccine may make it important to develop rapid tests to distinguish between them.