Welcome to Week 6. In this session, we're going to talk about containing disease outbreaks. But first, let's define terms. What exactly is an epidemic? Well, an epidemic is a sudden increase in the number of cases of a disease in a specified geographic area. In contrast, an outbreak is similar to an epidemic in that is a sudden increase in the number of diseases, but usually in a more limited geographic area. This image is titled a SARS epidemic map, but really to be more accurate, it should be a SARS pandemic map. A pandemic is an epidemic that spans several countries or even continents and affects a large number of people. Public health laws determine the function of public health departments. They authorize public health functions and appropriation of funds. In the US Constitution, as you recall, states and local governments are the ones with primary responsibility for public health. The role of the federal government is to assist the states and local governments when they lack the expertise or resources when responding to outbreaks. How do we detect and respond to outbreaks? Well, in humans, we have to do disease surveillance and investigation, we have to conduct quarantine for people who are healthy and isolation for those who are ill. We have to close public places such as schools, theaters and other public venues. We have to vaccinate or provide medications, assuming that they're available and in animals, the situation is similar in that you again have to do disease surveillance and outbreak investigation to find out how the outbreak is spreading, what's causing it. Again, quarantine and isolation of the animals, vaccination and medications if they're available. But in contrast to humans, we do have the option to cull herds, which we do not have with humans. So what are some disease surveillance strategies? Well, we have National Vital Statistics, birth and death statistics. A laboratory surveillance network is important to identify an increase in the number of cases of a particular microbe. We do not have a comprehensive national animal health monitoring program, we do not conduct routine surveillance of wildlife, fish, companion animals and food animals. Now, we do have some surveillance of wildlife, we do have some surveillance of food animals, but we do not have a comprehensive overview of all the different types of animals that live in our borders. In addition, a National Environmental Health Program is needed to conduct widespread surveillance of the soils, water and the air. We do have some segments of that, but it's not cohesive in an overarching fashion. So to identify an outbreak, first, the front-line people are physicians, other health care workers and laboratories that will report an increase in the number of microbes or diseases in a particular hospital. They'll report it to the state or regional health department, which will then go on to report to the National Disease Control Center. As I said, laboratories will report an increase in the number of concerning microbes that they will test. Whole genome sequencing is a very important method of detecting an increase in a particular micro, because we can track the entire genome of the microbe. So epidemiologists will conduct surveillance of the microbes source and spread. How do we manage disease outbreaks? Well, first, we have to prove that an outbreak actually exists through the previous methods of outbreak detection. You have to establish the diagnosis, you have to identify the microbe, the causative agent and the disease that it causes. You have to generate a case definition which specifies exactly what are the signs and symptoms of the disease that the microbe is causing. You have to investigate the number and count the cases to tell you how it's spreading and ideally, you create an epidemic curve. An epidemic curve will help to determine who is at risk. So as soon as possible, once you establish all of these criterion, you want to implement disease control measures. As this point source outbreak curve shows, you have a single incubation period where you have one food handler or a source of contaminated food contaminating and infecting a group of people. Along the y-axis again, number of cases, along the x-axis, the dates and in contrast to the single point-source curve, this is a continuous such as a contaminated well and you have a continuous ongoing number of cases of patients getting sick. Now, this is a graph of the cholera outbreak of 1854 that John Snow investigated and the pump handle was removed right about here. The case has started petering off and then dramatically ended the outbreak once the pump handle was removed. Now, in contrast to the previous outbreak curves that I showed you, this is a propagated or progressive source outbreak. Along the y-axis, you have the number of cases, x-axis, you have the dates. This is an example of measles in which you have an index case that infects, the first wave of infection. This first wave of infection will then go on to infect the second wave of infection. Let's talk about the basic reproductive number or R-naught. R-naught has a little zero right under it. R-naught is the measure of the transmissibility of a microbe in a completely unvaccinated population. So the higher the R-naught, the more infectious the microbe and the harder it is to contain the outbreak. So ideally, if you want your outbreak to die out, you want to have R-naught be less than one, because if the R-naught is greater than one, then the outbreak is going to continue to spread. In other words, you can think of R-naught as the number of people that one infectious person can infect. So if you have an R-naught of two, then one sick person will infect two other people and those two other people will go on to infect two more people each and the chain of reaction continues. Let's talk about herd immunity and R-naught. Now, R-naught as I said in the previous slide, is the transmissibility of a microbe in a completely unvaccinated population. Herd immunity, in contrast, is considered R. R is the transmissibility of a microbe in a highly vaccinated population. So R is similar to R-naught, R is in a vaccinated population, R-naught is in an unvaccinated population. In both circumstances, we want them to be less than one for the outbreak to die out, it's a lot easier to get R less than one through an effective vaccine, than it is in a completely unvaccinated population. Measles is a highly transmissible microbe with an R-naught ranging from 12-18 and that's why having a vaccine against measles is so important, because this disease is very infectious. Smallpox was not as infectious as measles, but still it was infectious enough to spread and cause a lot of death. Polio, also spread by the fecal-oral route, has a similar R-naught as smallpox and we go on down the line. Fortunately, influenza is generally not as infectious as measles, and Ebola has a much lower R-naught than the others. There are a number of outbreaks separation strategies. For example, in the Middle Ages, the concept of quarantine were to keep ships in port and not allow the people to disembark in an attempt to keep a disease from spreading. Quarantine then is used to separate and restrict the movement of people who are healthy, but are potentially exposed because you don't want them to be spreading the disease. In contrast to quarantine, isolation is used to keep the sick people away from healthy people. People will stay in quarantine until the infectious period of the microbe has ended. If a person is exposed to a microbe on day 1, but doesn't show signs and symptoms until day 7, then the quarantine period must last seven days to allow for that person to show whether or not they're going to get sick. So for example, the quarantine period for Ebola is 21 days. Now, what does that mean? Once people start exhibiting signs or symptoms of a disease, then they must go into isolation. Isolation is to keep the sick away from the healthy. So you can have isolation wards. For example, a negative pressure room will keep the microbe from spreading through the air by keeping it contained within the room. People will stay in isolation until they are no longer infectious or they die. During the 1918 influenza pandemic, there was no vaccine. So the best you can do is quarantine or close public spaces. So schools, theaters, stadiums, churches, and other venues were closed in an attempt to keep people away from each other and diminishing the spread of the disease. These policies, though, are likely to generate opposition from businesses and from other affected institutions. Shelter-in-place is usually used during crisis situations such as severe weather, bomb threats, or chemical or radiological hazards. People are encouraged to stay indoors and safe until they're told to evacuate. If there is no vaccine and no treatment, sometimes this might be the best option to reduce social interactions, but it would likely be met with non-compliance and opposition. A contentious public health decision is whether or not to make vaccination voluntary or mandatory during an outbreak. In 1809, Massachusetts passed the first law mandating vaccination against smallpox. This was an effort to prevent or control smallpox outbreaks. Other states then subsequently passed similar laws. Recall that vaccination and other public health measures are a state and local responsibility, so these decisions had to be done on a state-by-state basis. In the landmark 1905 case of Jacobson versus Massachusetts, the US Supreme Court ruled that states had the right to enforce and mandate vaccine requirements. In 1922, the Supreme Court found that mandatory school vaccinations were constitutional as well. Despite public vaccine hesitancy or reluctance to get children vaccinated, the courts have continued to uphold and support states mandatory vaccination laws. So to reiterate, there are no federal vaccination laws. All vaccination laws are state by state, and they vary according to each state. Three states have no vaccine exemptions, so you have to get vaccinated if you want to send your child to school. Some states have religious exemptions. Some states have both religious and philosophical exemptions. Each state has vaccination requirements for school, but again, they vary and some lax vaccination laws, such as with the measles vaccine means that it's much harder to achieve herd immunity in a population and with a disease like measles that is so highly communicable, very hard to contain. Unfortunately, there's been a long history of anti-vaccination sentiment. You can see from this cartoon here from 1894, again, showing the dangers of vaccine. In 1902, there was an Anti-vaccination Society of America. So this is not a new phenomenon. Controlling disease outbreaks is much harder to do without using a vaccine. As we can see, there's been a resurgence of measles because of concerns about the measles vaccine. If no vaccine is available, prophylactic medications, assuming they're available, either an antibiotic or an antiviral would be used to try to treat the disease or even prevent it. For example, during the anthrax crisis of 2001, an antibiotic stockpile was used for exposed postal workers to try to prevent them from coming down with the disease. So it helps to have a stockpile of antimicrobials in the event of an outbreak. But that's assuming that antimicrobials are available. In the US, there is a Strategic National Stockpile in the event that state and local governments run out of their stockpiles. Let's quickly review animal outbreaks. There are no national animal health programs that monitor the health of companion animals, food animals, and wildlife for potential zoonotic threats, including food borne illnesses. In contrast to human health, which is typically overseen by the Department of Health and Human Services, there is no one agency that oversees animal health. Instead, it's divided across a number of departments and agencies. The US Department of Agriculture, for example, monitors food, animals and wild animals, particularly for chronic wasting disease in deer, elk, and moose. The US Fish and Wildlife Service, which is part of the Department of the Interior, enforces the Endangered Species Act and monitors wild species in their habitats. The Centers for Disease Control and Prevention primarily oversees human health, but they will collect reports of rabies in different animals. Finally, at the international level, the World Organization for Animal Health, or the OIE, focuses on the health of livestock, not companion animals, and not wildlife. In the event of a deadly outbreak, there is the option to cull or kill large herds or flocks as needed. This is an image of the culling of chickens in an attempt to contain the avian influenza outbreak in China in 2015. To compensate for their losses, governments typically will reimburse farmers. While it might be effective, the culling of animals is logistically difficult for a variety of reasons, including the ethics of it. Since the international health regulations have been revised, the World Health Organization has reported a number of cases of outbreaks of international concern. Let's talk about the International Health Regulations. They were initially written in 1969 to contain three diseases, cholera, plague, and yellow fever. These three diseases were to be reported to the international community in the event of an outbreak. But the events of 2003, the SARS epidemic in China, led to a revision of the International Health Regulations. What happened to cause this change? Well, China withheld information from the World Health Organization and from other countries about its worsening public health crisis. Because of this withheld information, that contributed to the emergence then of the pandemic that lead to over 8,000 cases, over 700 deaths in almost 40 countries. In 2005, the International Health Regulations were revised. They became a legally binding international treaty that require countries to report any outbreak that had potential international concern. This did not restrict the outbreaks to particular diseases, but any disease could become a potential global concern. Questions for this section then include, what is the difference between an outbreak, an epidemic and a pandemic? What do public health laws do? How does quarantine differ from isolation? Why is it desirable to get R less than one? How might this be achieved? Why does measles require such a high vaccination rate to achieve herd immunity? During an outbreak, should vaccinations be mandatory or voluntary and why? Finally, why were the International Health Regulations revised in 2005 and how were they changed? With that, I'd like to thank you for your time and attention.
