Ethics Statement This clinical study was conducted under the United States (US) regulations for Exception from Informed Consent for Emergency Research (21 CFR 50.24) and the Canadian TriCouncil Policy Statement: Ethical Conduct for Research Involving Humans in Emergency Health Situations (Article 2.8). The protocol was reviewed and approved by the US Food and Drug Administration and Canadian Institute for Health Research. The protocol was also approved by all participating Institutional Review Boards (US) and Research Ethics Boards (Canada), as previously described [21]. Blood samples were drawn from healthy volunteers (controls) after obtaining written informed consent in accordance with the principles of the Declaration of Helsinki and with the approval of the institutional review boards of the participating hospitals in Washington, Toronto, and Boston.