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Table 1 The 48 possible risk factors worth investigating for Influenza A(H1N1)pdm09 mortality through a targeted literature search in Pubmed (with a focus on 2000–2013)a

From: Possible explanations for why some countries were harder hit by the pandemic influenza virus in 2009 – a global mortality impact modeling study

Factor type Factor Factor variable Association highera Association lowera References
Environmental Pollution Particulate matter   [28]
Ozone  
Climate Low temperature/low humidity   [10, 25, 26]
Physiological comorbidities in adults Immunosuppression other than HIV renal disease, chronic disease, cancer, etc.   [5]
Obesity BMI > 30   [3, 7]
Morbid Obesity BMI > 40   [44]
Pulmonary Disease COPD, other   [5]
Immunosupression HIV   [57]
TB   
HIV on ARTs   [57]
Physiological comorbidities in children Neurological Disorders Prevalence in children   [11]
Cerebral Palsy and developmental delay   [13]
Congenital Heart Disease   [13]
Asthma and immunosupression   [30, 40]
Treatment Antiviral Use Antiviral Drug Distribution   [31]
Antiviral within 48 h.   [23, 28, 30]
Late onset antiviral   [3, 31, 32]
Healthcare Healthcare expenditure Access to healthcare   [23, 24]
Prompt treatment and available options  
Physician knowledge and H1N1awareness  
Demographics Population age structure Preschool age   [9]
Pediatric patients   [15]
% < 15   [16]
% > 60 [16, 17]
Children at home   [34]
Ethnicity Alaskan/A.Indian/New Zealand aboriginal   [71]
Hipanics and blacks   [13]
Children of S. Asian descent   [16]
pH1N1 Viral Factors Strain variation by country Start of the pandemic   [30, 38, 39]
Pandemic peak  
Co-circulation
Viral shedding/ transmission Longer shedding in younger people   [72]
Longer shedding under optimal climatic conditions   [26]
Longer shedding in immunocompromised people   [8, 72]
Longer shedding or higher viral loads in those with severe disease  
Shorter shedding in those treated with antivirals within 48 h   [8]
Disease severity Pathogenic strains   
Data or modelling issues Variation in case finding by country -Clinician awareness    
-Diagnostic availability
-Testing protocol
-Breadth of surveillance
Pandemic preparedness activities Policies Quarantine   [35]
Activities Treatment, education  
Case finding efforts Outreach and method
Quickness of response Timing to mobilize community
Other Factors CDC Multiplier     [43]
International flight traffic International flights coming and going   [36]
  1. a “Association Higher” indicates those factors that may be risk factors for mortality. “Association Lower” indicates those factors that may be protective against mortality. Some factors are found to be both risk factors and protective factors in the literature and this is indicated with two check marks in the table