Risk Factors Linked to Influenza-like Illness as Identified from the Mexican Participatory Surveillance System: Risk Factors in ILI

Internet-based monitoring of influenza-like illnesses (ILI) has become more common since its beginnings nearly a decade ago, both through estimates based on the number of searches for influenza-related terms (e.g., Google flu trends), or by means of participatory surveillance systems. The latter, often seen as ways of engaging people in matters of scientific and public health importance, gather a wealth of potentially valuable epidemiological information complementary to that obtained through the established disease surveillance networks and also usually absent from search-based web algorithms. We present a statistical analysis of the data from the Mexican monitoring website "Reporta" by which the risk factors linked to reporting of ILI symptoms as outcome among its participants are determined, and interpret these results based on current knowledge of the factors that influence transmission of infection resulting in disease. Besides standard factors associated with enhanced susceptibility to infection some novel behavioral factors linked to high risk were: (i) use of public transport; (ii) frequent contact with animals, and (iii) use of non-standard interventions, such as homeopathy. While close contact with large groups of people in public transportation is generally assumed to be important in disease spread, frequent contact with animals is not. Our results are consistent with previous observations that animals may serve as mobile fomites and hence increase the propensity to develop disease. We conclude that analysis of rich information sets from Internet-based systems may suggest novel ideas on disease spread that are worth following up with field research.