Supplementary data are available at http://humrep.oxfordjournals.org/. Long-term respiratory follow-up of H1N1 infection BACKGROUND: The first case of 2009 pandemic influenza A (H1N1) virus infection was documented in our Hospital on 10th August 2009. METDODS AND FINDINGS: Real-time reverse-transcriptase-polymerase-chain-reaction (RT-PCR) testing was used to confirm the diagnosis. All patients were treated with oseltamivir from the first day of hospitalization. Upon admission 12/44 had local patchy shadowing in their chest x-ray and additionally antibiotic regimen was added to these patients as pneumonia was suspected based on clinical evidence. In total 44 patients were hospitalized 15/44 had asthma, 6/44 COPD, 5/44 leukemia. Lung function was evaluated with forced vital capacity, forced expiratory volume in 1 sec and diffused carbon monoxide upon discharge and every 3 months, until 6 months of observation was completed after discharge. The purpose of this retrospective cohort study was to evaluate whether influenza A (H1N1) had an impact on the respiratory capacity of the infected patients. CONCLUSIONS: An improvement of pulmonary function tests was observed between the first two measurements, implicating an inflammatory pathogenesis of influenza A (H1N1) to the respiratory tract. This inflammation was not associated with the severity or clinical outcome of the patients. All patients had a mild clinical course and their respiratory capacity was stable between the second and third measurement, suggesting that the duration of respiratory inflammation was two months. Early treatment with antiviral agents and vaccination represent the mainstay of management. The first human infections with the new influenza A (H1N1) virus were confirmed in April 2009 in America, but the infection had been rapidly spreading around the world and in June 2009 World Health Organization (WHO) declared a pandemic [1] [2] [3] [4] [5] . WHO had advised countries in the northern hemisphere to prepare for a second wave of pandemic spread [6] . To date, almost all countries in the world have confirmed a second wave of H1N1 virus [7, 8] . For this reason a working group of WHO member states agreed on a pandemic influenza preparedness framework [9] . The reason for creating this framework began with the need for real time virological data exchange among laboratories in different countries upon a pandemic outbreak [10, 11] . The H1N1 virus has resulted from a triple recombination containing genes from human, avian, and swine influenza virus [12, 13] . The incidence, clinical characteristics and factors affecting the patients outcome of the first wave have been well described in previous published studies [14] [15] [16] [17] . However, while the numbers of positive H1N1 patients were lower, the hospitalisation rates were higher in comparison to the numbers and rates of 2009. In addition, the proportion of hospitalised cases admitted to intensive care units (ICU) was higher in 2010. The reason for these differences are not yet completely clear. There has been no obvious change in the severity of pandemic influenza A (H1N1) 2009 disease thresholds for hospital and ICU admission [8] . Three possible explanations were given. First, a new pandemic influenza A (H1N1) genetic variant predominated in the winter 2010 influenza season [7] . The Influenza A (H1N1) 2009 strain had undergone mutation in the hemagglutin. This mutation was associated with severe clinical outcome in comparison to the usual influenza A (H1N1) 2009 strain [7, 18, 19] . Secondly, resistance to oseltamivir developing from the first wave reached a peak in the 2010 pandemic [20, 21] . Thirdly, it has been reported that this year's seasonal vaccine effectiveness was moderate, suggesting an insufficient protective effect against the second wave of influenza A (H1N1) [22] [23] [24] [25] [26] [27] .