Influenza surveillance among outpatients and inpatients in Morocco, 1996-2009

Abstract

Background: There is limited information about the epidemiology of influenza in Africa. We describe the epidemiology and seasonality of influenza in Morocco from 1996 to 2009 with particular emphasis on the 2007-2008 and 2008-2009 influenza seasons. Successes and challenges of the enhanced surveillance system introduced in 2007 are also discussed.

Methods: Virologic sentinel surveillance for influenza virus was initiated in Morocco in 1996 using a network of private practitioners that collected oro-pharyngeal and naso-pharyngeal swabs from outpatients presenting with influenza-like-illness (ILI). The surveillance network expanded over the years to include inpatients presenting with severe acute respiratory illness (SARI) at hospitals and syndromic surveillance for ILI and acute respiratory infection (ARI). Respiratory samples and structured questionnaires were collected from eligible patients, and samples were tested by immunofluorescence assays and by viral isolation for influenza viruses.

Results: We obtained a total of 6465 respiratory specimens during 1996 to 2009, of which, 3102 were collected during 2007-2009. Of those, 2249 (72%) were from patients with ILI, and 853 (27%) were from patients with SARI. Among the 3,102 patients, 98 (3%) had laboratory-confirmed influenza, of whom, 85 (87%) had ILI and 13 (13%) had SARI. Among ILI patients, the highest proportion of laboratory-confirmed influenza occurred in children less than 5 years of age (3/169; 2% during 2007-2008 and 23/271; 9% during 2008-2009) and patients 25-59 years of age (8/440; 2% during 2007-2009 and 21/483; 4% during 2008-2009). All SARI patients with influenza were less than 14 years of age. During all surveillance years, influenza virus circulation was seasonal with peak circulation during the winter months of October through April.

Conclusion: Influenza results in both mild and severe respiratory infections in Morocco, and accounted for a large proportion of all hospitalizations for severe respiratory illness among children 5 years of age and younger.

Figure 1. Number of positive influenza samples by type and subtypes and proportion of ILI cases over total consultation in the health unit and private clinic networks by week, Morocco, 2007–2009.

Figure 2. Onset peak and duration of influenza seasons, Morocco, 1996–2009.

Figure 3. Observed and predicted (using the Interrupted Time Series Analysis) numbers of samples during the pre- and post-intervention period, Morocco, 1996–2009.