Now, let's talk about some specific examples of surveillance objectives. First, we're going to talk about surveillance objectives within the context of tuberculosis. Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis. It primarily affects the lungs of humans, and people become infected through inhaling infectious particles that have been coughed into the air by another patient who has pulmonary tuberculosis. So, it's transmitted from person to person but through infectious particles in the air. Now, someone can be infected with tuberculosis without having any signs of disease for many years sometimes even decades. Some people who are infected with tuberculosis never develop any disease for the rest of their life, and they never know that they've been infected. People who don't have any signs and symptoms of disease are not infectious, it's only those who actually develop disease in their lungs, and then can cough those particles out into the air who are actually infectious. So, it's important to treat those people to limit transmission. So, the best prevention strategies we have from a public health perspective for tuberculosis are prompt diagnosis and treatment, because if someone is coughing particles into the air, they're going to be infectious until we treat them and the bacteria is no longer growing in their lungs. In the United States, we also treat people who've been infected but haven't developed disease yet. Now, this doesn't happen in all countries, it doesn't happen in most countries but in the United States where we do treat these people, identifying people who have been infected even before they develop symptoms is an important public health goal. So, within the context of tuberculosis, what are some possible surveillance objectives that we might have? Imagine that you're a senior public health official for your state or province, wherever you live, you are responsible for ensuring that you have the data required for effective public health action to prevent TB. What are some possible objectives for your TB surveillance program? I want you to stop right now, take five minutes to yourself, write down some possible surveillance objectives around TB. When you have a few ideas chalked out, go ahead and come back to the lecture and we'll talk about some possible ideas that you could have. All right. So, here are some of the objectives for TB surveillance that I've thought of in my home state of Maryland. One could be looking at time trends and incident TB cases for the State of Maryland. I think as a public health official I would want to know, are newly diagnosed cases increasing or decreasing? I would expect that if our public health systems are working well, we're finding cases early and we're treating them that the number of new cases diagnosed every year would be decreasing or at least staying the same. If I saw that cases we're increasing, it might suggest that there's a lapse in some of our public health surveillance programs. So, that might be one specific objective I would have. Now, another objective might be to identify outbreaks of tuberculosis in Maryland. That would also give us a strong signal that there is a gap and treatment and services particularly at high-risk venues. So, for example, in places where people are often in very close contact with one another, such as prisons or within hospital settings, TB can spread very fast. So, outbreaks could be sign that there are lapses within those specific kinds of institutions. Now, we can look for outbreaks of TB in Maryland by looking at cases. But in even more effective way to find outbreaks into conduct public health surveillance for outbreaks is to look at the genetic sequences of the TB organisms that come from patients. So, if you have a group of patients that have the exact same tuberculosis strain, that's highly suggestive there's an outbreak. So, if that were our surveillance objective, this surveillance would really be laboratory-based and we'd be asking the laboratory to identify those TB bugs that have the exact same genetic sequence. A third possible surveillance objective would be to identify deaths from tuberculosis in Maryland. So, this wouldn't tell us necessarily about time trends or about outbreaks, but it would be really important for us to understand lapses in treatment, this is a treatment failure if someone dies from TB, we should be able to find people who are sick and give them treatment. So, a death is a signal that something has gone wrong, and we would want to then further investigate why the treatment was unsuccessful. With this surveillance objective, we'll be asking questions about whether or not a delayed diagnosis was the cause of the death? Or perhaps the patient had comorbid condition such as HIV which contributed to the death? Or even perhaps the patient had a drug-resistant strain of tuberculosis? So, the drugs we typically use were unsuccessful. These are just a few examples and maybe you thought of different ones for your surveillance, but these are very common objectives for TB surveillance. In this lecture, we're going to talk about another disease and about surveillance and case definitions for this disease. The disease is Nipah virus and the case example is from Bangladesh. I spent a lot of my career working in Bangladesh on this system in particular. So, Nipah virus is an emerging infection. Cases have been detected each year since 2001 in Bangladesh. It's a bat-borne virus and humans are infected through drinking date palm sap that's collected from date palm trees, which is contaminated by the saliva or urine of Pteropus bats. Now, if the bats are infected, they can be [inaudible] the virus in their urine or saliva, that contaminates the sap and when humans drink it they become infected. The bats are large, fruit bats, there's a photo of one here shown flying against a blue sky, and they're really very cute. They're very important for the ecology of Bangladesh. But they do carry Nipah. Nipah is particularly concerning from a public health perspective because once a person is infected from a bat, they can infect other people. We sometimes see large outbreaks that are propagated through person-to-person transmission. Nipah virus causes severe illness. The first symptom is fever and sometimes with a cough, this progresses very quickly to altered mental status or coma, usually within a few days. Many patients will also have difficulty breathing, some have seizures which is a sign of neurologic involvement and infection in the brain, and the case fatality is over 75 percent. So, most patients who get Nipah virus do not survive. So, what might a surveillance objective for Nipah virus be? Well, Nipah has been named by the World Health Organization, the WHO, as one of the most dangerous emerging pathogens that we know of, and that's because of its ability to transmit from person-to-person and because most people in the world are susceptible. So, it could cause large outbreaks if it were to become more easily transmissible. Therefore, our surveillance objective for Nipah is to identify outbreaks, so that we can respond and try to prevent that onward person-to-person transmission. We also, as a secondary objective, want to describe the year-to-year variations and incidence of Nipah and Bangladesh, because we're trying to understand when and where people get infected, and what determines risk to humans.
