The purpose of this observational study is to characterize individuals in Mexico who seek medical care for influenza-like illness (ILI) and Severe Acute Respiratory Infection (SARI), describe seasonal pattern of the pathological agents associated with ILI and SARI and to identify changes in severity of disease caused by a specific agent.

The La Red Network clinical sites will enroll individuals presenting with ILI symptoms. A systematic sample will be chosen across all sites, with the goal of choosing 3 subjects who are outpatients and 3 subjects who are hospitalized every week at each site. It is recognized that, during seasons of low ILI activity, this enrollment goal may not be achieved. To be eligible for selection, subjects must be willing to sign informed consent, or provide informed consent/assent in the case of minors.

Subjects will be followed for a period of 28 days after enrollment to assess vital status. It is estimated that this study will enroll a maximum of 1872 subjects per year for an approximate 7488 subjects in the four years that the study proposes to enroll, depending upon the extent of ILI occurring during the period of this study.

Nasopharyngeal swabs, sputum samples, and blood samples will be obtained at enrollment. The nasopharyngeal swabs and, in adults > 18 years of age, portion of the blood for serum and peripheral blood mononuclear cells (PBMC) will be obtained for storage and shipped to the central repository located at the Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán for respiratory pathogen testing including real-time Polymerase Chain Reaction (PCR) and multiplex techniques.

All enrolled subjects will be assessed at enrollment, at 7 days (+3 days) and at 28 days (+/- 5 days) after enrollment to assess disease resolution and vital status.

The purpose of the study is to provide information regarding the pathogens causing ILI among patients seeking care at the La Red Network sites. The systematic collection of data over time will allow for the determination of seasonal patterns of different etiologic agents and the ability for early identification of the emergence of particular viruses, as well as the ability to identify changes in severity of disease signaled by an increase of severity, hospitalization and/or death attributable to a specific pathogen.

One important aspect of influenza infection is to the need to identify genetic factors associated with severity among patients who present with influenza and develop severe disease. Subjects will be given the option to opt out of the genetic testing by noting it on the informed consent form. This testing will be limited to studies related to respiratory viruses and influenza, and any study designed to use genetic testing. These studies will be submitted for review by the institutional review boards (IRBs) of the sites participating in the La Red Network.

Inclusion Criteria:

• Signed informed consent by participant. In pediatric subjects, signed informed consent by the parent(s) or legal guardian(s) and, as required by the Institutional Ethics Committee (IEC), signed assent by participant.

• An acute respiratory infection with:

  • Measured fever of ≥ 38°C or history of fever;
  • Cough; and
  • Onset within the last 10 days.

Exclusion Criteria:

• Onset of ILI illness while hospitalized for any other cause to avoid enrollment of potential nosocomial infections (nosocomial).
• Subjects previously included in this study within the last 30 days of enrollment.
• Having been cared for in the hospital for a period >24 hours.

Subjects will be selected from hospitalized (within the last 24 hours) patients and outpatients that seek medical care due to ILI at the sites of La Red Network and meet inclusion criteria. Those who accept participation will be invited to participate, the study will be explained and informed consent will be obtained. The study population will include children and pregnant women.