National Laboratory Surveillance of Influenza in Macedonia during Four Seasons

The aim of the study is to comprehend results of the influenza lab surveillance system in the Republic of Macedonia after the 2009 pandemic and to determine the main characteristics of four consecutive epidemic seasons (from 2010/2011 until 2013/2014).

As part of the universal surveillance system, nasal and throat specimens were collected from patients. After extraction of RNA, the CDC real-time RT-PCR assays for the detection of influenza types and subtypes were performed.

Out of 920 tested samples, 406 (44.1%) laboratory confirmed cases of influenza were found. Influenza activity begins as early as December and continues until the end of April with peaks in January or February with predominant influenza A and A/H1N1pdm. Influenza A viruses start their activity at week 49 to 52 and subside at week 17. Usually two peaks appear, the first one between week 2 and 4 and the second one between week 6 and 9. Subtype A/H1N1pdm was dominant among influenza A types in the 2010/2011 and 2012/2013 seasons. A/H3N2 was the only circulating influenza virus in the 2011/2012 season. Influenza B season is shorter and has only one peak, between weeks 2-5. Usually the influenza B viruses emerge in later stages than influenza A viruses, except for the first post-pandemic season.

Results revealed that post-pandemic influenza seasons in Macedonia were rather different. Although the influenza season pattern is similar to patterns in some countries of the WHO European region, some unique characteristics were observed.