Source: Writing Committee of the WHO Consultation on Clinical Aspects of Pandemic (H1N1) 2009 Influenza
Downloaded from www.nejm.org on May 6, 2010
Risk Factors for Complications of or Severe Illness with 2009 H1N1 Virus Infection.
Risk Factor Examples and Comments
1. Age <5 yr Increased risk especially for children <2 yr of age; highest hospitalization rates among children <1 yr
2. Pregnancy Risk of hospitalization increased by a factor of 4 to 7, as compared with agematched nonpregnant women, with highest risk in third trimester
3. Chronic cardiovascular condition Congestive heart failure or atherosclerotic disease; hypertension not shown to be an independent risk factor
4. Chronic lung disorder Asthma or COPD, cystic fibrosis
5. Metabolic disorder Diabetes
6. Neurologic condition Neuromuscular, neurocognitive, or seizure disorder
7. Immunosuppression Associated with HIV infection, organ transplantation, receipt of chemotherapy
or corticosteroids, or malnutrition
8. Morbid obesity – but not yet proved to be an independent risk factor for complications requiring hospitalization or ICU admission and possibly for death
9. Hemoglobinopathy Sickle cell anemia
10. Chronic renal disease Renal dialysis or transplantation
11. Chronic hepatic disease Cirrhosis
12. Long history of smoking Suggested but not yet proved to be an independent risk factor
13. Long-term aspirin therapy in children Risk of Reye’s syndrome; drugs containing salicylates should be avoided in children with influenza
14. Age ≥65 yr Highest case fatality rate but lowest rate of infection
* COPD denotes chronic obstructive pulmonary disease, HIV human immunodeficiency virus, and ICU intensive care unit.
† Morbid obesity is defined as a body-mass index (the weight in kilograms divided by the square of the height in meters)
of 40 or more.
