Traditional notifications of outbreaks rely on reporting by laboratories and hospitals. This type of monitoring was fine before high-speed travel was common. Today, rates of infections have increased and we need especially strong vigilance for initial indications of an infectious outbreak.
People respond in a variety of ways to illness–some can be tracked, others can not be. The behavioral possibilities include:
- visiting an emergency roommaking an appointment at a medical clinictreating themselves with over-the-counter medicationcontinuing daily routines without experiencing symptoms
These variations of behavior add a probabilistic characteristic to rates of infections. It is confusing to monitor the reactions of other people. In order to predict the dynamics of an infectious disease, epidemiologists search for clues about the responsible mechanisms at the individual level by answering these two questions:
What is the pathogenic agent? (virus, bacterium, or parasite)How is it transmitted? (air, food, or bodily fluids)
Individual modeling of disease trajectories has a long history. Eighteenth century mathematician Daniel Bernoulli created mathematical models for smallpox to support the use of inoculations. At the turn of the twentieth century, British physician Ronald Ross began to develop mathematical models to help him understand malaria’s trajectory, rate of progression, and probability of infection. He received the Nobel Prize in Physiology or Medicine in 1902.
This work laid the foundation for modern systems, and six tracking parameters researchers used over one hundred years ago continue to be relevant.
timegeographic locationpopulation densitycontact ratesaturationpersonal characteristics of those who contract the disease
Today, technology and communication have added complexity to patterns of infection with dramatic increases in incident rates. We continue to need to remain vigilant. Below are some of the contemporary issues societies face.
- global air travel increases the rate contact and spreads diseases along unpredictable vectors;aggressive pharmacologic treatments increase evolutionary pressure of pathogenic agents;vaccination policies alters the rate of exposure;timely responses like isolating exposed individuals blocks the spread of disease;seasonal contact rates again alters the rate of exposure.
People are anxious about epidemics and media adds to the drama. Keep in mind though that the next time we experience a harmful and contagious disease, social responses will be confusing until the class of the pathogen and the method of its transmission are clearly identified. The clarification of these two characteristics of a disease will provide a realistic way to protect people.