Crowding, an established risk factor for many infectious diseases, can increase the likelihood of pathogen transmission. In the United States, urban poverty and Hispanic and Asian ethnicity are correlated with domestic crowding; even at higher income levels, Hispanic and Asian households are relatively more crowded than white and African-American households (15) . In addition, in the United States, low-income persons, African Americans, and nonwhite Hispanics are more likely than persons in other groups to obtain regular medical care at emergency departments and publicly funded clinics (10) , where airborne transmission of infectious agents has been documented. Because these locations typically do not segregate sick and well patients and are becoming increasingly crowded (16) , patients waiting for care in these settings are likely to have greater exposure to infl uenza viruses and other respiratory pathogens. Another source of increased exposure to infected persons is public transportation, where persons from low-income and minority households account for 63% of users (17) .