Complete the following passage using words from the list A-L in the box below. A. sore B. severe C. connect D. infect E. pandemic F. epidemics G. commonly H. Unfortunately I. initially J. expected K. suspected L. runny Influenza, (1) called "the flu," is an illness caused by RNA viruses (Orthomyxoviridae family) that (2) the respiratory tract of many animals, birds, and humans. In most people, the infection results in the person getting a fever, cough, headache, and malaise (tired, no energy); some people also may develop a (3) throat, nausea, vomiting, and diarrhea. The majority of individuals has flu symptoms for about 1-2 weeks and then recovers with no problems. However, compared with most other viral respiratory infections, such as the common cold, influenza (flu) infection can cause a more (4) illness with a mortality rate (death rate) of about 0.1% of people infected with the virus. The above is the usual situation for the yearly occurring "conventional" or "seasonal" flu strains. However, there are situations in which some flu outbreaks are severe. These severe outbreaks occur when a portion of the human population is exposed to a flu strain against which the population has little or no immunity because the virus has become altered in a significant way. These outbreaks are usually termed (5) . Unusually severe worldwide outbreaks (pandemics) have occurred several times in the last hundred years since influenza virus was identified in 1933. By an examination of preserved tissue, the worst influenza (6) (also termed the Spanish flu or Spanish influenza) occurred in 1918 when the virus caused between 40-100 million deaths worldwide, with a mortality rate estimated to range from 2%-20%. In April 2009, a new influenza strain against which the world population has little or no immunity was isolated from humans in Mexico. It quickly spread throughout the world so fast that the WHO declared this new flu strain (first termed novel H1N1 influenza A swine flu, often later shortened to H1N1 or swine flu) as the cause of a pandemic on June 11, 2009. This was the first declared flu pandemic in 41 years. Fortunately, there was a worldwide response that included vaccine production, good hygiene practices (especially hand washing), and the virus (H1N1) caused far less morbidity and mortality than was (7) and predicted. The WHO declared the pandemic's end on Aug. 10, 2010, because it no longer fit into the WHO's criteria for a pandemic. Researchers identified a new influenza-related viral strain, H3N2, in 2011, but this strain has caused only about 330 infections with one death in the U.S. Since 2003, researchers identified another strain, H5N1, a bird flu virus, that caused about 650 human infections. This virus has not been detected in the U.S. and easily spreads among people in contrast to other flu strains. (8) , people infected with H5N1 have a high death rate (about 60% of infected people die). Currently, H5N1 does not readily transfer from person to person like other flu viruses.