Anthrax Bioterrorism Modeling, an Analysis of Prepositioning Antibiotics and PODS, Part 2

Our continued conversation with Dr. Sid Baccam addresses his basis for determining incubation periods for anthrax and the benefits and challenges of prepositioning antibiotics versus the benefits and challenges of Points of Dispensing (POD) access. If you missed the first part of the interview, click here.

Since there has never been a widespread anthrax attack, what did you use as a basis for determining incubation periods for anthrax? Besides the 2001 attacks, the only other real widespread anthrax event took place in Sverdlovsk, Russia in 1979. At that time, the Russians weren’t forthcoming with information about the event. Later, a team of American researchers went into Russia to investigate. They found out that it was an aerosol release of anthrax spores from a bio-weapons facility. It took a couple of years to get the data on incubation period and mortality rates. But there are many caveats that come with that because it was 12-13 years after the event and it is unclear whether we got all the data. No one is walking into this with blinders on thinking this is perfect data that has been compiled on incubation periods for anthrax.

IEM has used a couple of different sources for determining incubation and casualty estimates. One model was developed by Rickmeier et al. and has been used by the North Atlantic Treaty Organization (NATO) to estimate casualties caused by chemical, biological, radiological, or nuclear (CBRN) weapons. Another model we have used is one being developed and currently under consideration to replace Rickmeier et al. for use by NATO. Finally, we use an incubation model based on what happens inside a person who inhales anthrax spores.

IEM uses all three to model the incubation period. We are not at the point of saying any one of the three is better than the others. We would love to work with the best scientists out there–folks at the CDC and NIH–to dissect the data. We’d like to look at aspects of each of the three competing models to figure out if there’s one of three that is better. Or are there parts from each of the three models that we could use to make our own model?

In the years since the 2001 anthrax attacks there has been much talk about pre-positioning antibiotics for rapid dispensing to the public in the event of an attack. What are the benefits of prepositioning? What are the weaknesses?

One of the projects we’ve done for HHS was to look exactly at that—how do we dispense antibiotics more quickly? We’ve got three competing modalities— postal delivery, prepositioning, and Points of Dispensing (PODs).  One of our studies was to compare all three of them.

There have been three Postal delivery drills to test whether using USPS to deliver antibiotics directly to homes is feasible; we were fortunate enough to observe two of those drills in Philadelphia and Boston.  The thinking is that very few agencies or companies actually interact with the entire public on a daily basis – but Postal carriers do.  I saw first-hand that the Postal carriers could deliver antibiotics to houses and apartment buildings in a very timely manner – typically in less than 8 hours.  One of the large drawbacks to using Postal delivery of antibiotics is the fact that, currently, the plan is to deliver only one 10-day bottle of antibiotics to each household.  A major lesson that I learned was that if you let people do tasks that they are very familiar with, such as Postal carriers delivering mail, they are usually very successful.  Alternatively, if you ask people to do something they have never done before or very rarely do, such as working in PODs, you’re chances of success are not as good.

Prepositioning antibiotics in people’s homes has a lot of advantages because it cuts out all the logistics of distributing and dispensing the antibiotics. If the antibiotics are in homes, all you have to do is get on TV and tell people that they need to take the antibiotics in their kits. We can get people to start taking the antibiotics within hours. Conversely if they didn’t have the antibiotics at home, the Strategic National Stockpile (SNS) would physically have to ship the antibiotics to state and locals; the state and locals would have to activate all their workers, get the PODS set up, etc. You’re looking at probably a minimum of 24 hours before they could open PODs and hand out pills.

However, there are some weaknesses to pre-positioning. If the antibiotics are in people’s houses there’s always the potential for them to be misused. This is the biggest fear that people have, especially physicians. If people start misusing the antibiotics it can have a trickle-down effect and potentially increase the prevalence of antibiotic-resistant bacteria.

The other weakness that we found in our study is cost. If we are going to have medical kits for the public, who’s going to pay for them? Should the public buy them with their money? Would people spend money on something they may not perceive as necessary? And there is always a question of equity. Are we setting up a strategy that puts pressure on those that can’t afford the med kits, putting them at a disadvantage? This sets up the question of whether the government should pay for it, ship it, and cover all the costs. One of the legal issues with the government providing the med kits is that if the government were to provide them, the antibiotics would be considered a prescribed medication. Prescribed medications legally expire in one year, even though we know that the shelf life on these antibiotics is 8-10 years. You can imagine the cost of the federal government replacing antibiotics every one to two years for the entire American public.

The other concern is that terrorists could engineer anthrax so that it’s resistant to the prescribed treatment for anthrax. If you prepositioned antibiotics to the original strain in the homes, it will not be effective against the re-engineered strain and we’d have to depend on another mechanism to get people the antibiotics that might work. And the money spent on prepositioning is now wasted.

You have been studying the efforts related to POD access and have created a modeling and simulation tool for such purposes. When you are considering planning for PODs, how detailed do the simulations analyze the situation?

At the beginning we try to keep it simple and then add layers of complexity. For example, we ask the questions “when can you open PODs and how long does it take to get the antibiotic dispensed?” It starts getting very complex when we get into the logistics of distributing to state and locals. We want to know the logistics and that’s why we model not only the inside of the POD but the outside of the POD. What does it look like when people try to drive there—what is traffic congestion like; what about parking issues? Once you open the PODs, the stream of people coming into them is not uniform. It will come in fits and spurts, creating quite a mess. That’s one of the reasons we decided to look at the inside and outside of the POD to see what challenges people might be overlooking.

Your biomodeling work for HHS was cited in the recent NAS/IOM report entitled “Prepositioning Antiobiotics for Anthrax.” How did you become involved in the IOM report, and what did you do?

The IOM (Institute of Medicine) held a two-day workshop to hear presentations about the potential benefits or disadvantages of prepositioning antimicrobials at home. IOM has been aware of the medical consequence modeling and simulation work that we have done for HHS. In 2008, I was invited to participate in an IOM workshop to discuss different strategies for dispensing medical countermeasures for public health emergencies (Download full Dispensing Medical Countermeasures Workshop summary). Since that workshop, we have modeled the potential benefits of prepositioning medical countermeasures for HHS. So, IOM invited me to participate in their workshop on prepositioning antibiotics for anthrax. I was present on two panels for both days with several other modelers. They asked us about how our modeling was performed and what important aspects of modeling were included or not. We were able to provide them with our published studies as well.

Download full Prepositioning Antibiotics for Anthrax study.

Thank you, Dr. Baccam for your knowledge and insights. We appreciate the thorough work you’ve done to help improve preparedness for events involving Anthrax and Category A bioterrorism agents.

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