A new study published in the journal Influenza and Other Respiratory Viruses concluded that every person who is infected with the H1N1 swine flu puts 1.5 other people at risk over the three days before coughing, fever, and other symptoms appear.

The researchers said that anyone showing early symptoms of the flu needs to contact their health-care provider immediately. In addition, anti-viral drugs will likely help slow transmission.

The currently circulating swine flu first appeared in the town of La Gloria in Veracruz state in Mexico apparently sometime in early March. By March 15, it had spread to Mexico City and, since then, to much of the world.

More than 209,400 cases of swine flu have occurred globally, with at least 2,185 deaths. These numbers likely underestimate the outbreak, the World Health Organization noted.

The new study looked at Mexico City data on all suspected cases of H1N1 swine flu from April 15 to April 25, examining people they had been in contact with, and cross-referencing that information with the onset of symptoms, hospitalization and other factors.

The authors of the study concluded that the 2009 H1N1 virus is spreading at a rate comparable to the 1957 and 1968 flu pandemics–the most recent pandemics prior to this year’s swine flu–and to the Severe Acute Respiratory Syndrome outbreak, which surprised the world in 2003.

(via US News and World Report)