Epidemic Math For Dummies

 

     The Ebola epidemic is resulting in the addition of 150 active monitoring cases in the United States per day.  The established active monitoring period is 21 days.  On the 21st day, the first 150 people, assuming they are asymptomatic, are removed from the program and 150 more are added due to air travel.  Assuming no additional influx, for example through undocumented immigration, that equates to a baseline of 3000 active monitoring cases steady state (assuming we do not stop air travel to the United States from epidemic West African countries).  If we assume the basic reproduction number, with active monitoring, is reduced to 1.0 (from current estimates in West Africa of 1.7), and assume that 1% of the active monitoring cases become symptomatic, and assume that each case which becomes symptomatic has 10 high risk contacts prior to isolation, then the number of active monitoring cases, given only those considered high risk are tracked, nearly doubles approximately every 6 months and the number of infectious isolations continues to increase.

 

Baseline        1% of baseline     Monitoring Cycles   High Risk Contacts/infection

3000      +     [ ( 30                 X   9  (6 months)    )            (10)]                             = 5700

 

     Given that active monitoring does not include more than self reporting to health officials of temperature, and that 20% of infections do not present with temperature, and that risk factors do not consider population density of the monitored cases environment, as well as influx factors from venues other than air travel which are not as closely monitored, the above math is optimistic precluding a travel ban.