Epidemiologists (aka disease investigators) use a number of tools to estimate the contagiousness and spread of a disease. One such tool is the R0 (R nought), which represents the average number of people one sick person will infect. It’s calculated by estimating the chances of exposure, number of susceptible persons, length of contagious period, how the disease spreads, and how much time passes between exposure and becoming contagious.
For example: the HIV virus has an R0 of 4. One person with HIV, on average, infects 4 others. Remember, SARS, the respiratory scare in 2003? That also has an R0 of 4. Measles, on the other hand, has an R0 of 18. You can see why public health responds so quickly to a single positive measles case.
For Ebola, the R0 has been estimated at 2. So on average, one person infects two others. It doesn’t mean that Ebola is less serious than SARS, measles or influenza – it just means it doesn’t spread as easily as they do.
The goal of public health in an outbreak is to bring the R < 1. When that happens, spread of a disease stops and sick patients don’t infect others. In the case of Measles, this can be done by vaccinating exposed persons and reducing the sick person’s exposure to others.
In the case of Ebola, the focus is on quick identification of cases, isolation (literally using barrier and containment methods to keep patients from infecting anyone else), and identification of case contacts, monitoring them, and isolating any that are a suspect case. ADHS is providing guidance to hospitals on this strict infection control policy, and will continue to update them as the recommendations change.