key: cord-353871-mzw600ys
authors: Kowalczyk, D.; Cieślak, K.; Szymański, K.; Brydak, L. B.
title: The Activity of Influenza and Influenza-like Viruses in Individuals Aged over 14 in the 2015/2016 Influenza Season in Poland
date: 2017-02-15
journal: Respiratory System Diseases
DOI: 10.1007/5584_2016_202
sha: 
doc_id: 353871
cord_uid: mzw600ys

Infections in every epidemic season induced by respiratory viruses, especially by the influenza virus, are the cause of many illnesses and complications which often end in death. The aim of this study was to determine the activity of influenza and influenza-like viruses in individuals aged over of 14 in Poland during the 2015/2016 epidemic season. A total of 5070 specimens taken from patients were analyzed. The presence of the influenza virus was confirmed in 40.2% of cases, among which the subtype A/H1N1/pdm09 (62.6% positive samples) predominated. The analysis of confirmed influenza and influenza-like viruses in individuals divided into four age-groups demonstrate that the highest morbidity was reported for the age ranges: 45–64 (13.1%) and 26–44 (12.6%) years. An increase in the number of influenza type B cases (23.7% positive samples), which was the main cause of morbidity in the age group 15–25 years, was noticeable. Given the epidemiological and virological data, the 2015/2016 season in Poland was characterized by increased activity of the influenza virus compared to the previous season. In the 2015/2016 season, there were more than 3.8 million cases and suspected cases of influenza and influenza-like illness, more than 15,000 hospitalizations, and up to 140 deaths.

Influenza is an infectious viral disease of the respiratory system, caused by influenza viruses belonging to Orthomyxoviridae. There are three types of the influenza virus: A, B and C, among which infections caused by type C are asymptomatic. In every epidemic season, infections are induced by influenza virus type A and B, with usually a different course of illness for either type of virus, which also depends on the patient's age and the immune system's efficiency (Brydak 2008) . Influenza A virus is divided into subtypes, depending on the combination of the surface antigens hemagglutinin (HA) and neuraminidase (NA). There are 18 types of HA and 11 types of NA described (Wu et al. 2014) . Improperly treated infections caused by influenza viruses can lead to complications and consequently to death. Therefore, it is important to confirm the presence of influenza virus in a short period of time, using molecular biology methods (Bednarska et al. 2016b) , which enables to apply antiviral drugs, i.e., neuraminidase inhibitors, soon after onset of symptoms (Fiore et al. 2011; Brydak 2008) .

The 2015/2016 influenza season was characterized by an increase in the number of cases and suspected cases of the influenza and influenza-like viruses, compared to the 2014/ 2015 season. There has also been a significant increase in deaths due to complications of influenza, the number of which was up to 135 in adult patients, compared with the mere 11 fatal cases in the 2014/2015 season.

It is meaningful that in adult patients qualified to high-risk groups, e.g., those over 65 years of age, influenza may lead to exacerbations of chronic diseases and may be characterized by an acute fulminant course (Mastalerz-Migas et al. 2015; Brydak et al. 2009 ). However, the percentage of vaccinated population was only 2.39% in this age range in Poland in the epidemic season in question, despite the fact that the majority of local governments make the vaccination available free of charge for people over 50 years of age (Brydak et al. 2012) .

The aim of the present study was to analyze the activity influenza and influenza-like viruses in people over the age of 14 in the 2015/2016 influenza season in Poland, according to the new reporting system (Bednarska et al. 2016a 

The isolated material was analyzed using the RT-PCR to confirm the presence of influenza A and B viruses. A Transcriptor One-Step RT-PCR Kit (Qiagen; Venlo, The Netherlands) was used for the RT-PCR reaction. A 20 μL reaction mix, consisting of RNase free water, buffer, primer F (5 mM), primer R (5 mM), and the transcriptor enzyme mix, was incubated with 5 μL RNA isolated from a sample. For each tested sample, an internal control amplification was performed. (H3N2), and B/Phuket/3073/2013 viruses, and RNase-free water was used for negative control. Before the amplification step, isolated RNA were reverse transcribed into cDNA at 45 C for 15 min. The cDNA was analyzed as follows: initialization step of 1 cycle at 95 C for 2 min, followed by 45 cycles of amplification consisting of denaturation at 95 C for 15 s, annealing at 55 C for 30 s, and elongation at 72 C for 20 s.

The presence of influenza-like viruses was confirmed in two steps by RT-PCR using RV12 ACE Detection Kit (Seegene; Seul, South Korea . 1) . There also were confirmed cases of influenza B in individuals over 14 years of age. This was actually the dominant type of influenza virus in persons aged 15-25. However, the highest number of cases of influenza virus type B was found in the persons aged 26-44 (n ¼ 201), far fewer in those aged 15-25 years (n ¼ 95), 45-64 years (n ¼ 85), and over 65 years (n ¼ 89) (Fig. 2) .

In the 2015/2016 influenza season, there were just 16 cases of influenza-like viruses reported, with RSV (n ¼ 6), PIV-3 (n ¼ 4), and ADV (n ¼ 3) reported most frequently and with individual cases of PIV 1, hCoV and RhV A/B virues.

The number of 3,864,731 cases and suspected cases of influenza and influenza-like viruses in the 2015/2016 influenza epidemic season in Poland was comparable to that present in the preceding season (NIPH-NIH 2015/2016). However, the number of hospitalizations and deaths due to complications increased dramatically. The number of deaths increased from 11 in 2014/ 2015 to 140 in 2015/2016 (Table 1) . Despite a comparable number of cases and suspected cases of influenza and influenza-like viruses, the number of confirmed cases increased to 40.2% in 2015/2016 up from 21.2% in 2014/ 2015 (Bednarska et al. 2016) . There also was a difference in the most frequent contagion between the two seasons, with subtype A/H1N1/pdm09 (62.6%) predominating in 2015/2016 as opposed to A/H3N2/ predominating the season before in persons over 14 years of age (Hallmann-Szelińska et al. 2016) . The present study demonstrates that subtype A/H1N1/pdm09 predominated in all age groups, except for 15-24 years old persons in whom virus type B was dominant (Fig. 2) . In both compared seasons, the highest incidence of influenza was reported in the age-groups of 45-64 and 26-44 years and the lowest one in the 15-24 years old persons ( Fig. 1) (Bednarska et al. 2016b) . Interestingly, the number of confirmed cases of influenza virus was the highest in the same age-groups of 45-64 and 26-44 years in the past 2013/2014 season (Bednarska et al. 2015) . We also found that the activity of RSV and PIV-3 was increased in 2015/2016 compared with that in the season before (NIPH-NIH 2015/ 2016).

The following strains were included into the influenza vaccine in the 2015/2016 season: A/California/7/2009(H1N1)pdm09, A/Switzerland/9715293/2013(H3N2) and B/Phuket/3073/ 2013. A particular attention should be paid to the A/California/7/2009(H1N1)pdm09 strain which was a vaccine component since the 2010/ 2011 season, and also caused most influenza cases in persons over 14 years of age in the currently evaluated season. Given that the percentage of vaccinated population in this age range in Poland ranks at a dismally low level and has a decreasing trend from 1.95% in 2011 to 1.37% in 2015 (Epimeld 2016) , it can be judged that that the recorded number of influenza cases reflects the immunodeficiency to this viral strain (Brydak 2015) .

An increased number of confirmed cases of infection in the currently evaluated season was mainly caused by the influenza virus and to a lesser extent by influenza-like viruses, which may lead to a severer disease course, complications, and in consequence to death. The death as a sequelae of influenza was due usually to complications arising from the underlying chronic comorbidities, especially cardiovascular and respiratory disorders that ended up in fulminant pneumonia. The present findings of 40.2% of confirmed cases of influenza and influenza-like viruses in the 2015/2016 influenza season show a near doubling of laboratory confirmations compared with past seasons (Bednarska et al. 2016b; Bednarska et al. 2015) . That result points to substantial improvements in infection surveillance and imbued nuances in the virological and epidemiological procedures despite a drastically low and inexplicably decreasing percentage of adult, mostly middle-aged, population getting vaccinated against influenza each epidemic season in Poland. The virological data presented in this article seek to call repeat attention to the need to vaccinate against influenza as the most effective method of preventing the infection and its severe complications, death included; a need advocated by the WHO, major medical societies, and 142 National Influenza Centers worldwide.

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Acknowledgments Funded by NIPH-NIH thematic subject 5/EM.1. The authors would like to acknowledge physicians and employees of VSESs participating in SENTINEL and non-Sentinel programs for their input into the influenza surveillance in Poland.

The authors declare no conflicts of interest in relation to this article.