Abstract
BackgroundInfluenza is a major cause of morbidity and mortality in Africa. However, a lack of epidemiological data remains for this pathology, and the performances of the influenza-like illness (ILI) case definitions used for sentinel surveillance have never been evaluated in Senegal. This study aimed to i) assess the performance of three different ILI case definitions, adopted by the WHO, USA-CDC (CDC) and European-CDC (ECDC) and ii) identify clinical factors associated with a positive diagnosis for Influenza in order to develop an algorithm fitted for the Senegalese context.MethodsAll 657 patients with a febrile pathological episode (FPE) between January 2013 and December 2016 were followed in a cohort study in two rural villages in Senegal, accounting for 1653 FPE observations with nasopharyngeal sampling and influenza virus screening by rRT-PCR. For each FPE, general characteristics and clinical signs presented by patients were collected. Sensitivity, Specificity, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) for the three ILI case definitions were assessed using PCR result as the reference test. Associations between clinical signs and influenza infection were analyzed using logistic regression with generalized estimating equations. Sore throat, arthralgia or myalgia were missing for children under 5 years.ResultsWHO, CDC and ECDC case definitions had similar sensitivity (81.0%; 95%CI: 77.0–85.0) and NPV (91.0%; 95%CI: 89.0–93.1) while the WHO and CDC ILI case definitions had the highest specificity (52.0%; 95%CI: 49.1–54.5) and PPV (32.0%; 95%CI: 30.0–35.0). These performances varied by age groups. In children < 5 years, the significant predictors of influenza virus infection were cough and nasal discharge. In patients from 5 years, cough, nasal discharge, sore throat and asthenia grade 3 best predicted influenza infection. The addition of “nasal discharge” as a symptom to the WHO case definition decreased sensitivity but increased specificity, particularly in the pediatric population.ConclusionIn summary, all three definitions studies (WHO, ECDC & CDC) have similar performance, even by age group. The revised WHO ILI definition could be chosen for surveillance purposes for its simplicity. Symptomatic predictors of influenza virus infection vary according the age group.
Highlights
Influenza is a major cause of morbidity and mortality in Africa
Influenza contributes substantially to the morbidity and mortality of respiratory infections, and the highest burden of severe disease is experienced by the < 5 and ≥ 65 years age groups [5]. This vaccine preventable disease is characterized by seasonal epidemics that occur throughout the world every year, and occasional pandemics arising from novel subtypes
Clinical predictors associated with positive Polymerase Chain Reaction (PCR) for influenza (Tables 5 & 6) In univariate analysis, only cough, nasal discharge, headache, asthenia, diarrhea and dyspnea were found to be significantly associated with a positive PCR for influenza in all age group
Summary
Influenza is a major cause of morbidity and mortality in Africa. a lack of epidemiological data remains for this pathology, and the performances of the influenza-like illness (ILI) case definitions used for sentinel surveillance have never been evaluated in Senegal. Acute respiratory infections (ARIs) are a major cause of morbidity and mortality in most African countries, especially in children under five years. Influenza contributes substantially to the morbidity and mortality of respiratory infections, and the highest burden of severe disease is experienced by the < 5 and ≥ 65 years age groups [5]. This vaccine preventable disease is characterized by seasonal epidemics that occur throughout the world every year, and occasional pandemics arising from novel subtypes. Almost all influenza-associated deaths in children (99%) occur in developing countries [7]
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