INFLUENZA AND INFLUENZA-LIKE ILLNESS IN GENERAL-PRACTICE - DRAWING LESSONS FOR SURVEILLANCE FROM A PILOT-STUDY IN PARIS, PRANCE

Background. There are two types of inflenza surveillance techniques: q ualitative laboratory-based surveillance and quantitative medical prac tice-based surveillance. The former is of great importance in isolatin g new strains of the virus, which helps in the decision-making process concerning the composition of the vaccine, and the latter provides es timates of morbidity, mortality or economic impact as a result of infe ction from the influenza virus. Rapid methods such as immunoflourescen ce (IF) or immunocapture assays (ICA) are now available for diagnosis of influenza infections. However, little is known about the use of the se methods for influenza surveillance purposes. Aims. To evaluate the feasibility of a rapid influenza diagnosis in ambulatory conditions, a nd to investigate the therapeutical outcomes of patients suffering fro m influenza-like illness (ILI) in relation to the virological diagnose s.Method. During the 1994-1995 influenza season, 130 patients presenti ng with ILI symptoms (<36 hours) to 33 general practitioners (GPs) wer e included in a prospective study. Two nasal swabs and one throat swab per patient were collected and sent to the laboratory within 12 hours . Information concerning therapeutical outcomes was recorded during ex amination. Specimens were analysed using the immunofluorescence (IF) m ethod and antigen immunocapture assay (ICA). Results. Sixteen influenz a A (12%) and 19 influenza B (15%) infections were diagnosed. The over all rate of influenza positive specimens was 17% in the pre-epidemic p eriod and 31% during the epidemic (P=0.1). The rates of usable specime ns for IF assay, nasal ICA and throat ICA were 46%, 100% and 99% respe ctively. The combination of these three collections ensured a highly s ensitive influenza virological diagnosis. There were no differences in therapeutical outcomes between the influenza positive and negative ca ses. The GPs prescribed antibiotics in 60% of the cases for a mean dur ation of 7 days (+/-1.2). The mean duration of sick leave was 3.4 days (+/- 1.6). Twelve patients (four influenza positive, eight influenza negative) had been vaccinated at the beginning of the winter. The prac titioner's intuition concerning 'which patient should be tested for in fluenza virus' did not prove useful in improving the aptness of virolo gical diagnoses in the field of influenza surveillance. Conclusion. Th e only way to estimate the true impact of influenza is to carry out a systematic virological sampling based on a sensitive clinical definiti on and using sensitive laboratory methods.