The incidence, natural history and associated outcomes of influenza-like illness and clinical influenza in Italy

Objectives. This study investigated the epidemiology, natural history and resource use associated with influenza in the general population setting in Italy. Methods. For a 3-month winter epidemic period, 202 GPs reported daily the number of visits performed for influenza-like illness (ILI), clinical influenza and any other cause. In addition, the first 10 cases of clinical influenza requiring a doctor's visit in each month of the 3-month period and for a total of 30 cases per GP were recorded carefully and followed-up, for evaluation of clinical evolution, associated outcomes and resource use. Results. Almost 200 000 visits were performed by 202 GPs, ILI and clinical influenza accounting for 13.8 and 8.3% of all-cause visits, respectively. A total of 6057 cases of clinical influenza were also recorded and evaluated for associated outcomes and resource use. Twenty percent of the patients were at risk because they were elderly (>65 years) or presented with concomitant chronic conditions. Almost all the patients received at least one prescription for symptomatic drugs and 36% received a prescription for antibiotics. Thirty-five percent of patients had at least one complication from influenza, primarily upper and lower respiratory tract bacterial infections. At-risk patients had a significantly higher complication rate (odds ratio = 2.89) and required more instrumental exams and hospitalizations compared with the general population, accounting for most of the direct costs associated with clinical influenza. Patients with clinical influenza had an average of 5 days absence from work or school. Conclusions. Influenza is associated with significant morbidity in the general and at-risk population, a high degree of resource use in the at-risk population and substantial reduction or loss of productivity in the active working Italian population.