1. National Transportation Safety Board. Enhance public helicopter safety, NTSB 2015 Most Wanted transportation safety improvements [cited 16 August 2017]. Available from: https://www.ntsb.gov/safety/mwl/Pages/mwl3_2015.aspx and https://www.ntsb.gov/safety/mwl/Documents/MWL_2015_Factsheet_03.pdf.
2. Special investigation report on emergency medical services operations,2006
3. An outbreak of community-acquired pneumocystis carinii pneumonia—initial manifestation of cellular immune dysfunction;Masur;N Engl J Med,1981
4. Essentials of epidemiology in public health;Aschengrau,2008
5. Epidemiology: an introduction;Rothman,2012