Review article

Pandemic Influenza A Virus (H1N1): Appearance in the First Two Seasons

Ilija Kuzman ; Klinika za infektivne bolesti ''Dr. Fran Mihaljević''
Elvira Čeljuska-Tošev ; Medicinski fakultet Sveučilišta u Zagrebu

Abstract

Pandemic influenza A virus (H1N1) has emerged in spring 2009. A more intensive wave in Croatia was recorded in the period from October to December 2009, and the disease was observed until March 2010. In the 2010/11 season, influenza was recorded from the beginning of December till the end of March 2011. Pandemic influenza A virus (H1N1) was almost the sole cause of the disease in the second season as well, because influenza B virus appeared only in the end of the epidemic and was poorly spread. The epidemiological and clinical features of the disease caused by pandemic influenza A virus (H1N1) do not differ significantly from those of seasonal influenza. However, there are major differences with regard to the time of appearance, age distribution, risk groups and complications. The most important difference lies in a higher morbidity and a higher number of complications and consequently mortality in patients below the age of 60 years, while the majority of complications and fatal outcomes caused by seasonal influenza have been recorded in patients above 65 years of age. The number of patients diagnosed with influenza and examined at the Clinic for Infectious Diseases “Dr. Fran Mihaljević“ in Zagreb in the 2009/2010 season was 3,856, out of whom 562 (14.6%) were hospitalized. The number of deaths among adult patients was 15. No child died. In the next season, influenza was diagnosed in 2,883 patients, out of whom 458 (15.9%) were hospitalized and 14 died. The average age of all patients diagnosed with pandemic virus was 30.2 years in the first season, and 40.3 years in the second season. In the 2009/10 season risk factors were recorded in 56.2% of patients diagnosed with influenza virus, and in the following season they were recorded in 50% of patients. In the first season complications were recorded in 69.2% of patients. In both seasons pneumonia was the most frequent complication. Primary viral pneumonia in young adults was recorded far more frequently in the first season, while bacterial pneumonia was more frequent in the second season, especially in the elderly above 65 years of age. The pandemic influenza in 2009/10 was significantly more severe and fatal than seasonal influenza, especially in young adults, although it did not affect a high percentage of citizens. The epidemiological and clinical features of pandemic virus significantly changed already the following season and were more similar to those of seasonal influenza.

Keywords

pandemic influenza; influenza A virus (H1N1); epidemiology; clinical presentation; risk factors; complications

Hrčak ID:

77356

URI

https://hrcak.srce.hr/77356

Publication date:

3.1.2011.

Article data in other languages: croatian

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