Who is that masked person: the use of face masks on Mexico City public transportation during the Influenza A (H1N1) outbreak.

This article examines three issues: (1) the use, over time, of facemasks in a public setting to prevent the spread of a respiratory disease for which the mortality rate is unknown; (2) the difference between the responses of male and female subjects in a public setting to unknown risks; and (3) the effectiveness of mandatory and voluntary public health measures in a public health emergency. The use of facemasks to prevent the spread of respiratory diseases in a public setting is controversial. At the height of the influenza epidemic in Mexico City in the spring of 2009, the federal government of Mexico recommended that passengers on public transport use facemasks to prevent contagion. The Mexico City government made the use of facemasks mandatory for bus and taxi drivers, but enforcement procedures differed for these two categories. Using an evidence-based approach, we collected data on the use of facemasks over a 2-week period. In the specific context of the Mexico City influenza outbreak, these data showed mask usage rates mimicked the course of the epidemic and gender difference in compliance rates among metro passengers. Moreover, there was not a significant difference in compliance with mandatory and voluntary public health measures where the effect of the mandatory measures was diminished by insufficiently severe penalties, the lack of market forces to create compliance incentives and sufficient political influence to diminish enforcement. Voluntary compliance was diminished by lack of trust in the government.