The World Health Organization has officially declared that we’re at the start of an influenza pandemic. Nearly 30,000 cases of swine flu/H1N1 have been confirmed in 74 countries, and the virus is spreading easily among people in multiple regions of the world. North America has had the highest number of cases so far – 13,217 in the US, 6,241 in Mexico, and 2,978 in Canada – and new cases are still being reported. (In fact, CDC’s count for the US, which tends to run ahead of WHO’s, is now at 17,855.)

Countries in the Southern Hemisphere are just entering flu season, and large numbers of cases have been confirmed in Chile (1,694) and Australia (1,307). The Washington Post’s David Brown quotes WHO Director General Margaret Chan explaining that H1N1 is crowding out the seasonal influenza virus, which is a typical feature of past pandemics.

Chan also emphasizes an important unknown about this virus: how it will behave in conditions typically found in the developing world. So far, swine flu has killed only 145 victims, but in her public statement Chan said, “It is prudent to anticipate a bleaker picture as the virus spreads to areas with limited resources, poor health care, and a high prevalence of underlying medical problems.”

We don’t know what will happen with this virus or how bad the pandemic will get. Keep washing your hands, covering your cough, and limiting your contact with others if you’re sick – and Revere also recommends getting a pneumococcal vaccine to prevent one of the serious common complications of influenza. This pandemic is also a good reminder that our politicians need to hear from us about the importance of a strong public health infrastructure, because our current facilities will be severely overtaxed if this virus comes back and wallops us in the fall.