Objective: To determine the frequency of infections caused by Influenza viruses, i.e. Influenza A (H1N1) pdm09, Influenza A (H3N2) and Influenza B in patients presenting with respiratory tract infections, i.e. influenza-like illness (ILI) and severe acute respiratory illness (SARI).

Study design: Descriptive, cross-sectional study.

Place and duration of study: Department of Virology, Armed Forces Institute of Pathology (AFIP), Rawalpindi, from October 2017 to February 2018.

Methodology: A total of 624 samples from patients with respiratory tract infections (both ILI and SARI) were included in the study. Specimens collected from the patients included nasal swabs and throat swabs, which were transported in viral transport medium (VTM) to Virology Department, AFIP. Multiplex PCR was done for Influenza A (H1N1) pdm09, Influenza A (H3N2) and Influenza B.

Results: A total of 200 (32%) samples were found to be positive for Influenza viruses. Out of total 624 samples analysed, 220 (35.3%) were from females and 404 (64.7%) from males. Among these, 510 (81.7%) presented with ILI and 114 (18.3%) with SARI. Among positive samples, 120 (19.2%) samples were positive for H1N1, 61 (9.8%) for H3N2 and 19 (3%) were positive for Influenza B. Highest number of positive cases occurred in the month of January, i.e. 148 (74%) cases. Only 3 (2.5%) patients out of 120 infected with H1N1 were in age group-I (0-5 years). While in age group-II (6-30 years), age group-III (31-60 years), and age group-IV (>60 years); 39 (32.5%), 63 (52.5%) and 15 (12.5%) patients were infected by H1N1, respectively. Maximum patients with H3N2 infection were in age group-III; 30 (49.2%) of the total 61. Commonest Influenza subtype in age group-IV was H3N2 found in 20 (32.8%) patients, followed by H1N1 in 15 (12.5%) patients.

Conclusion: The dominant subtype in our set-up, during winter of 2017-2018, was Influenza A (H1N1) pdm09. Highest numbers of positive cases were recorded in the month of January. People with ILI and SARI should be tested for Influenza viruses to avoid unnecessary use of antibiotics.