Epidemiology of Influenza among patients with influenza-like illness and severe acute respiratory illness in Pakistan: a 10-year surveillance study 2008-17.

BACKGROUND: In Pakistan, the burden of influenza was largely unknown as no formal surveillance system was in place. In 2008, an influenza surveillance system was set up in eight sentinel sites. This study describes the epidemiology of influenza virus using a 10-year surveillance data from 2008-2017. METHODS: Nasopharyngeal/throat swabs were collected from patients with Influenza Like Illness (ILI) and Severe Acute Respiratory Illness (SARI) along with relevant epidemiological information. The samples were tested using real time Reverse Transcriptase-Polymerase Chain Reaction for detection and characterization of influenza viruses. RESULTS: A total of 17209 samples were tested for influenza, of which 3552 (20.6%) were positive; 2151/11239 (19.1%) were patients with ILI whereas 1401/5970 (23.5%) came from patients with SARI. Influenza A/H1N1pdm09 was the predominant strain with 40.6% (n=1442) followed by influenza B (936, 26.4%). Influenza A/H1N1pdm09 was predominant among the children (5-14 years) and adults (15-64 years). Influenza B strain was predominantly found in the elderly age group (>65 years) accounting for 48% of cases in that age group followed by children (2-4 years) accounting for 37% of cases in that group. CONCLUSION: This 10-year surveillance data provides evidence of influenza activity in the country throughout the year with seasonal winter peaks. The results could be used to strengthen epidemic preparedness and response plan. This article is protected by copyright. All rights reserved.