Influenza is a well-known cause of acute respiratory disease. It is generally a self-limiting infection with systemic and respiratory symptoms, and usually resolves after 3–6 days in most patients. Viral clearance in the respiratory tract occurs after 3–5 days [ 1 x 1 Hayden, FG. Prevention and treatment of influenza in immunocompromised patients. Am J Med. 1997; 102: 55–60 Abstract | Full Text | Full Text PDF | PubMed | Google Scholar See all References 1 ]. However, a complicated course consisting of severe respiratory illness, exacerbation of underlying diseases and the need for intensive care has been reported for some patients [ 2 x 2 Thompson, WW, Shay, DK, Weintraub, E et al. Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA. 2003; 289: 179–186 Crossref | PubMed | Scopus (2490) | Google Scholar See all References , 3 x 3 Thompson, WW, Shay, DK, Weintraub, E et al. Influenza‐associated hospitalizations in the United States. JAMA. 2004; 292: 1333–1340 Crossref | PubMed | Scopus (1486) | Google Scholar See all References ]. The recently described pandemic influenza A(H1N1) virus had a more aggressive course in specific populations, such as young patients and pregnant women [ 4 x 4 Chowell, G, Bertozzi, SM, Colchero, MA et al. Severe respiratory disease concurrent with the circulation of H1N1 influenza. N Engl J Med. 2009; 361: 674–679 Crossref | PubMed | Scopus (526) | Google Scholar See all References , 5 x 5 Jamieson, DJ, Honein, MA, Rasmussen, SA et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet. 2009; 374: 451–458 Abstract | Full Text | Full Text PDF | PubMed | Scopus (899) | Google Scholar See all References ].