Hi, my name is Emily Gurley, and I'm on faculty at the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health. Today, we're going to talk about defining surveillance objectives and detecting cases. I hope that by the end of this lecture, you'll be able to list examples of objectives for public health surveillance. You should be able to define the components of a surveillance case definition, including elements that may be related to person, place or time. I hope you'll be able to identify at least three trade-offs between workload and quality for public health surveillance systems, as well as describe surveillance as an observation process. There are a few readings and resources that we recommend you read to really understand some of the concepts associated with this lecture. The first is a paper by Naser and colleagues, on the cluster surveillance for detecting encephalitis outbreaks in Bangladesh. That goes through examples of surveillance for Nipah virus in Bangladesh, and that's one of the examples we'll be using in this lecture. So, that will be useful for you. In addition, there are two resources here that describe surveillance objectives and how case definitions have been made in global systems of public health surveillance. The first is US CDC's Manual for Surveillance of Vaccine-Preventable Diseases. It goes into many details about a lot of different vaccine-preventable diseases and public health surveillance systems to detect those. Then there's another example from the Stop Cholera project, that proposes standardized, surveillance and case definitions for cholera worldwide. In this section, we're going to talk about surveillance objectives. What is the surveillance objective? The surveillance objective tells you what you're after in your public health surveillance program. So, it could include epidemiologic characteristics, it could include detection of something new, but importantly a surveillance objective is not a disease. Let me tell you what that means. So, for example, in the example of influenza, let's say, we would not say our surveillance objective is surveillance for influenza, we would need to be more specific than that. So, an objective is not just a particular disease, but what about that disease that you want to learn something new about, that you want to detect. Is it deaths due to that disease? Is it new cases of the disease at a certain state? Is it outbreaks of that disease at a certain time? The public health surveillance cycle is important to remember here. The public health surveillance cycle shows how we move from data collection, to analysis, to data interpretation, dissemination of results, and then very importantly back to public health action. So, the whole point of public health surveillance is to get to public health action. When we're thinking about what the objective is for surveillance program, we have to orient ourselves to ultimately what kind of action do we want? What is it that we're trying to improve about public health in particular? So, let's go through a few examples of types of objectives for public health surveillance and then some possible actions that might go along with those. Let's say for example, the objective of your public health surveillance is to identify disease trends. So you would be answering questions such as, is incidence increasing or decreasing over time? That might tell you or it might be able to answer the question, is our public health program working? So, for example, say you have a public health program to prevent this disease X. If you see that the disease is indeed decreasing over time through your surveillance, you may conclude that the public health program is working well. Now, a possible action coming from this kind of surveillance would be that you expand a program that's working well or perhaps change a program that isn't working well. Again, there's this very strong link between the objective of your surveillance system and the type of public health action that you want to achieve thinking about a public health surveillance cycle from data to action. Another example, might be outbreak detection. Say the purpose of your public health surveillance is to detect outbreaks. The action coming from that public health surveillance system would be the ability to respond rapidly to control an outbreak once you've detected it. That's very common objective from any surveillance systems. Another example of public health surveillance objective would be to find cases and treat them. A good example of this might be, HIV. Where if you find someone who's infected, they can benefit from treatment. They may not know they're infected. So, you may develop a surveillance program that actively just tries to find cases of infection because of the public health benefits that treatment could confer. So, again, you have a very strong link between your objective which is finding cases of infection, and then the public health action, which is increases in treatment, reductions in mortality or even reductions in transmission resulting from treatment. Finally, another common type of public health surveillance objective is to identify novel agents. So, we may want to know is there a new pathogen causing disease in this population? Influenza is a good example here because sometimes there are new influenza viruses that arise, sometimes from animal reservoirs, and they can cause large outbreaks. So, we may want to detect these as soon as possible and we may have surveillance systems that are designed specifically for this purpose with this objective in mind. Now, an action that might result from this surveillance, is that you implement new prevention and control measures specifically for that novel agent, or maybe you declare an outbreak and you may want to inform others in your region, in your state, in your country, so that they can also be on the lookout for this novel agent.
