<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The 2009 flu pandemic or swine flu was an influenza pandemic, and the second of the two pandemics involving H1N1 influenza virus (the first of them being the 1918 flu pandemic), albeit in a new version . First described in April 2009, the virus appeared to be a new strain of H1N1 which resulted when a previous triple reassortment of bird, swine and human flu viruses further combined with a Eurasian pig flu virus, leading to the term "swine flu". </P> <P> Unlike most strains of influenza, H1N1 does not disproportionately infect adults older than 60 years; this was an unusual and characteristic feature of the H1N1 pandemic . Even in the case of previously very healthy people, a small percentage will develop pneumonia or acute respiratory distress syndrome (ARDS). This manifests itself as increased breathing difficulty and typically occurs 3--6 days after initial onset of flu symptoms . The pneumonia caused by flu can be either direct viral pneumonia or a secondary bacterial pneumonia . In fact, a November 2009 New England Journal of Medicine article recommends that flu patients whose chest X-ray indicates pneumonia receive both antivirals and antibiotics . In particular, it is a warning sign if a child (and presumably an adult) seems to be getting better and then relapses with high fever, as this relapse may be bacterial pneumonia . </P> <P> Initially called an "outbreak", widespread H1N1 infection was first recognized in the state of Veracruz, Mexico, with evidence that the virus had been present for months before it was officially called an "epidemic". The Mexican government closed most of Mexico City's public and private facilities in an attempt to contain the spread of the virus; however, it continued to spread globally, and clinics in some areas were overwhelmed by infected people . In late April the World Health Organization (WHO) declared its first ever "public health emergency of international concern," or PHEIC, and in June the WHO and the U.S. CDC stopped counting cases and declared the outbreak a pandemic . </P>

World now at the start of 2009 influenza pandemic