Anthrax Bioterrorism Modeling, an Analysis of Prepositioning Antibiotics and PODS (Points of Dispensing)

IEM Computational Epidemiologist Dr. Sid Baccam has been working with the Department of Health and Human Services for the past 9 years developing models to analyze response to bioterrorism attacks involving anthrax or other bioterrorism agents. Dr. Baccam has been specifically focused on post-exposure prophylaxis (PEP) dispensing logistics and its impact on medical consequences. The results of his work were recently cited in a National Academy of Sciences (NAS)/Institute of Medicine (IOM) report that analyzed strategies for prepositioning antibiotics to improve response to a terrorist attack involving anthrax.

We sat down with Dr. Baccam to gain a deeper understanding of his work with anthrax and bioterrorism response planning.

What is the nature of the modeling and simulation work that you are doing for HHS?

We’ve been working with HHS since 2003, helping them and answer two basic questions—how many people could possibly become sick or die from different biological attacks and what types of medical intervention strategies can we employ to help mitigate the impacts of biological attacks. We build models and simulations to help senior decision makers better understand how a biological attack may play out depending on different response policies. We combine a lot of information in our models, from infectious doses required to cause infection in people, to how the diseases may progress in the presence or absence of medical interventions, and the speed of the public health response, so we can show decision makers the potential consequences.

It’s very hard for people to conceptualize all the moving parts and to know how different factors affect the outcome – that’s where our models are the most beneficial.

We can show decision makers how many people can become infected following an intentional attack with a biological agent. Based on different response strategies and the response speed, we can show them how many of these infected people could be saved by post-exposure prophylaxis (PEP) and how many people may still get sick and require hospitalization. Our modeling results help HHS answer their two main questions by showing how many people could become sick and whether some strategies they are considering may be better than others at preventing disease and saving lives.

Does your modeling focus solely on Anthrax?

CDC has a list of agents called Category A agents. These are the bioterrorism agents of most concern; anthrax is included in the list.  We’ve modeled all of the Category A agents. However the primary focus for HHS is anthrax because we’ve already experienced an attack with that agent being used.

How does your work address response to a bioterrorism attack in a new way?

Part of what we’ve been trying to do is look into the logistics, the concepts of operations for response to a bioterrorism event. It’s easy enough for someone to say an anthrax attack happened and we want to respond in 2 days. (This is an actual objective of the Cities Readiness Initiative (CRI) – having all CRI cities able to complete mass prophylaxis to their entire population within 48 hours.

Some of the modeling we do for HHS is breaking down what happens in the 48 hours after you push that red button and say go—the time when the antibiotics are being dispensed to citizens. We look directly at what things have to happen to reach the 48-hour goal. This involves looking at what the federal government has to do in terms of taking national stockpile assets and shipping them out to the state and local governments. Once the state and locals receive them, the onus is on them to start dispensing that to their population. We try to get into the logistics of this. We look at all the possibilities of “how long might this take?” and “how long might that take?

This is how we got into looking at the Points of Dispensing (POD) question. PODs are centralized locations such as schools or convention centers where the general public is directed to go to in order to pick up medication that can help protect them from becoming ill following a biological attack. When we talk about different modalities that can be used for post-exposure prophylaxis (PEP) dispensing, PODs will always be there. There are pros and cons to this. In 2008, the analogy “Every solution is Swiss cheese” was coined. Every solution covers some of the problem, but the problem is going to have holes. How do we cover those holes with other strategies? If you tried to cobble together multiple solutions, with all the Swiss cheese layers you’ve hopefully covered all the holes and have a complete solution that is effective

We are not aware of any other efforts besides ours that capture this kind of end-to end study. Some of the published papers that talk about dispensing use a start time of the actual opening of the POD and then see how long it takes to dispense the antibiotics. They disregard everything that led up to getting the antibiotic and POD set up. They make simplified assumptions that we don’t. You don’t just open the POD once and then you’re done. There is more that happens. For instance, not everyone will need to continue taking antibiotics. If we can narrow down the attack, we can identify the people that really need to continue taking antibiotics and those that can stop taking the antibiotics. The POD will need to reopen for a second dispensing of antibiotics, also known as follow-on dispensing.

More to come on our continued conversation with Dr. Baccam. Our next interview covers anthrax incubation periods and an analysis of prepositioning and Points of Dispensing (POD) access. Read Part 2 of Anthrax Bioterrorism Modeling interview.

Author:  An Interview with Dr. Sid Baccam, Senior Scientist – Computational Epidemiologist