Performance of case definitions and clinical predictors for influenza surveillance among patients followed in a rural cohort in Senegal

Abstract

Background Influenza 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. Methods All 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. Results WHO, 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. Conclusion In 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.

Detection of Rift Valley Fever Virus Lineage H From South Africa Through the Syndromic Sentinel Surveillance Network in Senegal

“…Sentinel sites were selected on the basis of criteria used by the MoH. A checklist of criteria was developed based on the WHO-recommended attributes for sentinel site selection including feasibility, representativeness, and the availability of data to enable disease burden estimate [ 25 ]. These sites are composed of community health care centers in decentralized areas in each Senegalese region and 3 reference hospitals in Dakar.…”

Yellow Fever Outbreak in Eastern Senegal, 2020–2021

“…Indeed, Senegal has a longstanding YF surveillance system, in the context of the WHO network of YF laboratories where the case definition is an acute onset of fever, with jaundice appearing within 14 days after the onset of the first symptoms [ 15 ]. In addition, since 2011, a nationwide Syndromic Sentinel Surveillance Network has been implemented in Senegal (4S network), coordinated by the Ministry of Health (MoH) and Institut Pasteur de Dakar [ 16 ]. Moreover and similarly to a previous viro-entomological surveillance program implemented from 2008 to 2013 [ 17 , 18 ], passive surveillance for arbovirus and hemorrhagic fever virus infections has been reactivated in the Kedougou region (12°32′ N, 12°11′ W) since early 2020 among patients presenting with acute febrile illness and attending 4 health facilities in Kedougou and Saraya districts: the Kedougou health district center, the Saraya health district center, the Bandafassi primary health care center and the Kedougou military camp.…”

Does knowing the influenza epidemic threshold has been reached influence the performance of influenza case definitions?

“…A study carried out in Singapore in 2005-2009 also found that the performance of the WHO case definition was better than the ECDC case definition (13.5 vs 9.7) [12]. In a study carried out in Senegal during 2013 and 2016, the WHO and ECDC definitions showed a similar performance, including by age group; the authors suggest the WHO ILI definition could be chosen for surveillance purposes due to its simplicity [13].…”

“…2.87). In the aforementioned Senegalese study, cough was significantly associated with influenza in children aged <5 and �5 years (OR 2.21 and 2.70, respectively) [13]. A study carried out in Illinois in 2009-2011 found that the best predictors of laboratory-confirmed influenza were cough followed by fever (DOR 6.39 and 4.7, respectively) [16].…”