Introduction

There are three groups of influenza virus: influenza A, influenza B, and influenza C. Both influenza B and C viruses are associated with low-level sporadic diseases and limited outbreaks, and they never cause a pandemic influenza. On the other hand, influenza A is most frequent, with more mortality than influenza B, and it is responsible for most seasonal influenza cases and all known pandemics. The outbreak of influenza virus that usually occurs annually each winter is called seasonal influenza, which typically increases in its incidence throughout the late autumn and begins to decline in mid spring. The most common signs and symptoms related to influenza, which can include all or some of them, are fever, headache, myalgia, prostration, coryza, sore throat, and cough.

These seasonal epidemics are caused by the accumulation of mutations in the antigenic sites of circulating influenza viruses, i.e., antigenic drift. However, antigenic shift is another mechanism of antigenic change by influenza virus type A, and it occurs when an antigenically distinct virus emerges in the human population. Such a virus has the potential to cause a widespread global epidemic with high morbidity and mortality. Although seasonal influenza epidemics generally occur during the winter in temperate climates, the transmission of the disease may occur throughout the year in the tropics.

Whilst the epidemiology and impact of influenza are well defined in developed countries, data in developing countries are still limited. All known subtypes of influenza A viruses can infect birds, so called avian influenza viruses, except subtypes A(H17N10) and A(H18N11), which have only been found in bats. Phylogenetically, all mammalian influenza viruses are derived from avian influenza viruses. Only two influenza A virus subtypes A(H1N1)pdm09, and A(H3N2), are currently circulating among people in the world.

Methodology

It is a cross-sectional study carried out in Baghdad by selecting the two hospitals responsible for receiving suspected influenza cases, which had been recorded according to the WHO definition and classified into either ILI cases, or SARI cases which need admission. One of them (Al-Numan hospital) located in the eastern side of Baghdad (Rusafa) and responsible for registration of cases with ILI and the other one (Al-Kadhimiya hospital) located in the western side (Karkh) and responsible for SARI cases registration. The sample size was all ILI and SARI cases recorded in those hospitals from November 2021 till June 2022.

The tools of the study are the epidemiological characteristics of the participants according to their filled out special standard case-investigation forms which were registered in the mentioned hospitals. These characteristics include the following variables: age, sex, living area, classification of case (ILI or SARI), presence of some health problems, status of immunization against influenza and COVID-19, type of influenza virus and its strain after laboratory analysis. The data were analyzed by PC-SPSS programme, and chi-square test (with significant p-value of ≤ 0.05) was done for comparison between those variables.

Results

The total number of confirmed influenza patients in this study was 69. All of them were of type A influenza virus. Out of them, 56 patients were registered as ILI cases and 13 patients were registered as SARI cases.

Discussion

During the specified six-month study duration, the total number of patients who had a confirmed laboratory diagnosis of positive influenza virus in Baghdad was 69. Most of them (81.2%) were diagnosed as ILI cases and recorded in Al-Numan hospital and they did not need hospitalization. Others (18.8%) were diagnosed as SARI cases and recorded in Al-Kadhimiya hospital and they were hospitalized, so they were considered as severe cases.

Most of the enrolled positive influenza cases in Baghdad (73.9%) aged eighteen years or more. This goes with the fact that influenza affects adults and elderly more than children. Slightly more than half of the patients in this study (53.6%) were females. The majority of patients with influenza virus in the current work (87%) lived in urban areas.

The vast majority of enrolled patients with influenza (91.3%) had cough and fever in their clinical presentation. This goes with the typical presentation of the disease. Concerning the presence of comorbidities, some of patients with influenza in this study had hematological disease (2.9%), immunological disease (2.9%), asthma (2.9%), diabetes mellitus (2.8%), chronic renal disease (2.8%), chronic lung disease (1.4%), heart disease (1.4%), muscular disease (1.4%), or neurological disease (1.4%).

About the immunization status of the enrolled patients with influenza virus in this study, only a very small percent of them (7.2%) got vaccinated against the virus. This reflects the low coverage rate of influenza vaccination generally among Iraqi people. More than two-thirds of the patients with influenza in the current work (65.2%) got immunized with COVID-19 vaccine.

Conclusion

(1.) Most of the confirmed influenza cases in Baghdad were of a mild grade. (2.) The detected type of influenza was only type A virus, where the H3N2 subtype constituted the vast majority of cases among them. (3.) The sex, type of living area, presence of asthma or an immunological disease were significantly associated with the severity of influenza viral infection.

Recommendation

(1.) Increasing the coverage of influenza vaccine in Iraq, especially against the influenza A-H3N2 subtype. (2.) Focusing on females, asthmatic patients, and those with an immunological disease, for raising their awareness about influenza and promoting them to get the influenza vaccine every year.