Influenza Sentinel Surveillance System Evaluation and Data Analysis – Nigeria, 2009-2010

Background: Influenza is an epidemic prone disease affecting mainly children and elderly people, causing considerable morbidity and mortality. In 2007 a human case of avian influenza was identified in Nigeria leading to establishment of a sentinel surveillance system in four sites for influenza-like illnesses (ILI) and severe acute respiratory infections (SARI) and a National Influenza Reference Laboratory for influenza virus detection. We evaluated the system and analyzed surveillance data to assess the pattern of influenza in Nigeria.

Methods: We evaluated the surveillance system using the CDC guideline. We analyzed demographic, clinical and laboratory data from 1st April 2009 to 31st August 2010.

Results: In average, 30 days (Range: 15-50 days) were required to complete sampling, specimens processing and dissemination of results (target: 18 days). Based on the case definitions, 15.6% of cases were misclassified. Stock-out of reagents and laboratory contaminations contributed to delays in turnaround-time, affecting the stability of the system. 1,378 males and 1,355 females were enrolled with mean ages 8.6 years and 10.8 years, respectively. 89.2% of patients were children below 17 years. Of 2,818 tested samples, 217 (7.7%) were influenza positive, of which 184 (84%) met case definitions for ILI (n=167) or SARI (n=17). Seropositivity rate increased between October 2009 and April 2010, peaking to 22.2% by February 2010. Influenza A constituted 97.3% positive samples, with pandemic H1N1 (2009) as the predominant subtype (55.9%), while 38 (2.7%) were influenza B.

Conclusion: Timeliness, data quality and stability should be improved by retraining of sentinel staff and timely provision of laboratory consumables. Seropositivity was high in dry season. Nigerian Government should preposition influenza vaccines before the onset of dry seasons in October. 

Author (s): 

Lilian S. Maina, A. Adedeji, I. Dalhat, P. Nguku, H. Akpan, M. Shehu

Presenter (s): 
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