Timely detection of bronchiolitis epidemics in Guadeloupe1

It is well known that early detection of epidemics is imperative to effective control; hence, infectious disease surveillance has been conducted in many countries for decades. Traditional methods of reporting diseases (e.g., notifiable disease surveillance, laboratory-based surveillance) are currently linked to less specific, but more reactive methods (1). These include syndromic surveillance, which makes it possible to identify illness clusters before diagnoses are confirmed (1–3), and mathematical models, which are often used to analyze surveillance data in order detect epidemics sooner (4–9). Throughout the world, acute bronchiolitis is a common lower respiratory tract infection and a leading cause of hospital admission among young children, especially those less than 2 years of age (10). In France, an estimated one-third of the infant population is affected each Objective. To develop a criterion for early detection of bronchiolitis epidemics in Guadeloupe so that prevention and control strategies can be implemented in a more timely manner. Methods. Weekly figures of bronchiolitis cases reported from July 2005–July 2010 by Guadeloupe’s sentinel network were used. The criterion for detecting epidemics was created with data from the 2005–2009 bronchiolitis seasons. First, the baseline level for bronchiolitis (BL) was predicted by fitting a periodic regression on the non-epidemic observations; then a test was conducted of nine possible criteria to define epidemics by combining a statistical threshold set at different levels and a number of consecutive weeks with observations above and below them; lastly, the optimal criterion was selected considering its performances using expert advice as the gold standard. The selected criterion was validated with data from 2009–2010 season. Results. The BL accounted for a linear trend and two sinusoidal functions of 52 and 26 weeks (R2 = 45%). According to the epidemic criterion selected, the statistical threshold was set at the upper limit of the one-sided 95% Confidence Interval of the predicted BL; 2 consecutive weeks with cases above it were necessary to set the start of an epidemic, and three again below to set the end. The median delay in launching the alerts was 2 weeks; there was one false alert; and the sensitivity, specificity, and positive predictive value for detecting epidemic weeks were 98%, 96%, 95%, respectively. During the validation period, the criterion launched one false alert and detected the epidemic with 4 weeks of delay. Conclusions. This criterion supports epidemiologists in timely interpretation of bronchiolitis epidemiological data for decision makers in Guadeloupe. In the future, it should be updated in accordance with trends in bronchiolitis epidemiology, and improved by integrating virological indicators. Its inclusion in an integrated management strategy for bronchiolitis prevention and control, supported by a bronchiolitis public health network, should also be encouraged.