Women wear masks as they wait inside a Mixcoac health center in Mexico City April 24, 2009. A deadly strain of swine flu never seen before has broken out in Mexico, killing at least 16 people and raising fears it is spreading across North America. The World Health Organization said it was concerned about what it called 800 "influenza-like" cases in Mexico, and also about a confirmed outbreak of a new strain of swine flu in the United States. REUTERS/Jorge Dan Lopez (MEXICO SOCIETY HEALTH ENVIRONMENT)
REUTERS/Stringer/Mexico