Usefulness of Clinical Definitions of Influenza for Public Health Surveillance Purposes

Domínguez, Àngela; Soldevila, Núria; Torner, Núria; Martínez, Ana; Godoy, Pere; Rius, Cristina; Jané, Mireia

A first limitation is that, in our sentinel surveillance network, fever was predefined as a temperature >37.8 • C, but the specific temperature was not reported. In our opinion, the impact of this limitation may be minimal, as other factors, such as individual and daily variations, the site of measurement, and the natural trend for physicians to round temperatures up or down, can influence the measured temperature [9] . Secondly, age, the influenza type and subtype [5] , or the season [18] might be partially responsible for differences in the performance of the variables studied. However, we adjusted for age and season, and it seems improbable that our results are invalid. Thirdly, during epidemic weeks, when physicians are aware of the onset of epidemic activity, the criteria for the sampling of suspected ILI patients might be less rigorous [28] , but we have analyzed the performance of case definitions and clinical manifestations during both epidemic weeks and in all weeks, and no relevant differences were observed. Fourthly, although frequent in studies based on surveillance data, the number of patients aged ≥65 years was quite low (only 7.9% of all patients studied).