The pandemic A/H1N1 virus was named "swine flu" when the current outbreak started. Although it is not yet confirmed that the index case acquired the virus from pigs, the nomenclature "swine flu" was due to the fact that the virus is triple-reassortant with genes from swine, avian, and human influenza origins. A total of 57,809 cases were reported in the WHO EMRO region, 693 of whom have died (1.2% case fatality). Lebanon had 1,838 confirmed cases with 5 deaths, it is estimated that 4% of these cases required hospitalization. Most cases of pandemic influenza presented with fever, cough, and sore throat. Other common symptoms included myalgia, headache, and rhinorrhea. The pandemic A/H1N1 virus appears to be very successful at human-to-human transmission. It is also causing infections beyond the traditional seasonal variation of previous human influenza viruses. Unlike seasonal influenza viruses that usually cause severe infections requiring hospitalization among the elderly and children under 5 years old, the pandemic A/H1N1 viruses are causing more severe illness among young adults. Several reports have associated certain underlying conditions with severe illness. Such conditions were pregnancy, asthma, diabetes, obesity, and heart disease.

This study will measure risk and protective factors associated with pandemic A/H1N1 infection. This study will also be able to estimate risk factors for severe illness requiring hospitalization or leading to death. These factors are: travel history, exposure to other confirmed or suspected cases, obesity, pregnancy, influenza vaccination history, residency in nursing homes, attendance of daycares, tobacco use, and other comorbidities (pulmonary diseases, cardiovascular diseases, diabetes, renal insufficiency). Unlike other descriptive studies, this analytical case-control study will enable to accurately measure the strength of association between potential risk factors and outcome. By isolating viruses from specimens collected from cases, this study will be able to characterize these viruses and document any genetic mutations or antiviral resistance.

The main objectives of this study are:

1. To investigate the risk factors of infection with the pandemic A/H1N1 viruses.
2. To characterize influenza viruses causing infection.
3. If enough severe cases were enrolled to make it statistically feasible, this study will investigate the risk factors of severe illness or death associated with infection with the pandemic A/H1N1 viruses.

Inclusion Criteria:

• Be willing to participate by signing a consent form/assent statement, and completing the study requirements.
• Be willing to provide nasal swab.
• Testing negative for influenza A/H1N1 by RT PCR to be enrolled as a control.
• Testing positive for influenza A/H1N1 by RT PCR to be enrolled as a case.

Exclusion Criteria:

• Any known immunosuppressive condition or immune deficiency disease (including HIV infection), or ongoing receipt of any immunosuppressive therapy. (Note that this study has chosen to exclude such populations because of their increased risk of acquiring infections, they are relatively few, and are not representative of a national sample).

Cases will be selected from the outpatient clinics and inpatient units at American Univeristy of Beirut thus the study team expect that selection bias would be minimal. Confirmed cases attending other healthcare facilities for whom contact information is available, will be contacted and invited to participate in this study. Controls will be selected from the outpatient clinics and inpatient units of the Internal Medicine, Family Medicine, and Pediatric and Adolescent Medicine Departments at AUBMC. Cases and controls attending the hospital will be from the same catchment area, thus coming from the same geographical areas, have similar socioeconomic status, and have similar chances of exposure to influenza viruses. Other influenza case control studies have matched on sex and enrolled hospital-based controls.