Next let's talk about a surveillance data reporting system within the United States. The National Notifiable Diseases Surveillance System that's run by the US CDC. This notifiable disease reporting system requires that states and territories report about a 120 different diseases that could pose a national risk. If you go to the CDC website, you can see a list of all of the diseases that are notifiable under the system. The list of diseases is updated periodically depending on what threats emerge. For example a recent inclusion was Zika virus once it started to cause outbreaks near the United States. The idea between this notifiable disease reporting system is that if we identify early public health threats within the US, we can contain them. Similar to the Global Thinking about the IHR, the US CDC's system of notifiable diseases relies upon the assumption that if we find threats early in one particular state, we can prevent spread further. This disease reporting system is primarily made up of infectious diseases, but also includes other non-infectious causes such as lead poisoning. There are 57 different reporting jurisdictions in the US. So, that's territories, states and the like that report to CDC's Disease reporting system. Let's talk just a moment about reportable versus notifiable. So, a reportable disease is a disease that must be reported with any given state or territory. In the United States, each state and territory has the autonomy to decide for itself which diseases they want clinicians and public health officials to report to them. These vary from state to state, but that's what a reportable disease is. It means that it has to be reported within the state or territory. A notifiable disease is at the central level at the CDC level. CDC requests that all of these jurisdictions, the territories and states report or notify them of diseases that are on their list. But this is a voluntary system. What complicates things a bit is that not all of the reportable diseases within a state are notifiable, and not all of the notifiable diseases from CDC's perspective are reportable within any given state or territory. So, you can imagine that there are some things that slipped through the cracks. Again, the system isn't perfect, but it does provide a framework for helping states think through what they should be reporting and what they should be notifying at the national level. Here's a brief schematic showing how this disease system works. So, at the very top you start with a patient who is ill. That patient seeks health care and if the health care team identifies that the patient has a reportable condition, then they report it to their public health department, either at the state or the territory level. Next is where CDC comes in. Because then its the state that decides to notify CDC about that condition. If it's on CDC's list of notifiable diseases, and the CDC Disease Program then can support outbreak, investigation, or support the states however they need in addressing this public health threat. So, while CDC is really only correlating the data at the end for the diseases that are notified to them by states and territories, you see other blue arrows going up to the other levels as well. So, they do provide information for patients when they should seek care for example, they provide guidance to health care teams and clinicians about how to treat certain diseases and how to diagnose it, they provide them with data on what is causing disease in their area or causing outbreaks throughout the country, and sometimes that helps health care teams think differently about differential diagnoses and could spur reporting to their local public health departments. Finally, CDC provides support to public health departments in terms of outbreak assistance, funding or even guidance on data collection. This system also is limited by capacity and incentives. If only identified diseases can be reported within a state or territory, then what's reportable? Again there's a link between the mandate to report and resource allocation. Let's just think of an example here. If you are in a state with severely limited resources for a public health surveillance, are you going to put those resources towards diseases where you're required to report to your state or where you're not? Well, practicality suggests that you're going to allocate those resources to diseases that you're required to report. Let's say that there are notifiable diseases to CDC that aren't reportable within your state. So, those states may be less likely to identify and report diseases that are notifiable. Simply because that's not part of their local state mandate. There's a link between how we allocate resources and the mandates for reporting when it comes to public health. Just like internationally, public health and outbreaks are political nationally as well. Ultimately, questions about jurisdiction are also important. Who's responsible for an outbreak? Is it the state or is that at the national level? Sometimes the boundaries aren't that clear. But ultimately, there's broad acceptance and use of this National Notifiable Disease Reporting System and all states have seen outbreaks in other places and learned about it through this system that's helped them better prepare for these emerging threats. So, there's broad buy-in on this system across the United States. I want to give you next an example of one outbreak that was monitored through this system. Since 2014, there's been an increase in cases in the United States of Acute Flaccid Myelitis. Now, this is a condition characterized by weakness in one or more of the limbs, and it has a variety of causes that include viruses or even toxins. In the US, they've been actively investigating case reports from across the US and even in 2018 the etiology of this acute flaccid myelitis outbreak is poorly understood. But this outbreak highlights the utility of a Notifiable Disease Surveillance Reporting System across the United States. Because ultimately, there are 29 states reporting cases. They're shown here on this figure and how they occurred over the course of four years. So, along the bottom, the x-axis, you see the month of onset and on the y-axis are the number of confirmed cases of acute flaccid myelitis. This is what's called an epidemiologic curve where cases are plotted over time by their onset dates. So, we can see that there's a seasonality to this disease. You can see peaks in late summer through October and many of the years, 2014, 2016 and again in 2018. Without the Notifiable Diseases system, these kind of data would be difficult to correlate and the states would be left to deal with these outbreaks on their own. Because acute flaccid myelitis is so rare, the ability to combine data across states is a real strength of this system because it allows clinicians and public health officials to investigate them as a group, as a whole so they can understand the phenomenon better.
