Basic Disease Investigation in Colorado Module 1: Communicable Disease Basics

Transcription

1 Basic Disease Investigation in Colorado Module 1: Communicable Disease Basics Introduction This course is designed for non-epidemiologists who work in public health, environmental health, and other healthcare fields who wish to expand their knowledge of epidemiology and disease investigation in order to conduct routine disease control and assist with disease outbreaks within the community. This course is the first of six modules that are being developed to enhance disease investigation and disease reporting in the state of Colorado. This course will take approximately one hour to complete. When you are finished reviewing the course information, click on the "Course Exam" link. You MUST complete and pass the course exam in order to receive credit for taking this course. This course also contains links to several websites and other useful resources. The "Resources" link on the home page contains all of the resources referenced throughout this course. The "Glossary" link provides a list of all defined terms used in the six disease investigation modules. This course will introduce you to basic communicable disease terminology, measures, and resources commonly used by practicing epidemiologists in the state of Colorado. This course will also prepare you to work collaboratively with epidemiologists and public health surveillance personnel in your region of the state. After completing this course, you will be able to: Identify the three components of the disease triangle of communicable disease theory Describe at least three routes of transmission and provide one disease example for each route Identify two resources for information about communicable diseases Define basic epidemiology terminology Communicable Diseases Communicable, or infectious, diseases are human illnesses caused by viruses, bacteria, parasites, fungi and other microbes. These diseases may be spread by direct contact with an infected person or animal, by ingesting contaminated food or water, by insects like mosquitoes or ticks (vectors), or by contact with contaminated surroundings like animal droppings or even contaminated air. With the introduction of antibiotics over 50 years ago, scientists made sweeping predictions heralding the end of death and suffering from infectious diseases. However, during the past 25 years, microbes have demonstrated their tremendous ability to adapt, survive and challenge us. Infectious diseases remain the leading cause of death worldwide. Of the top ten causes of death compiled by the World Health Organization for 2004, five were due to infectious diseases. In the United States, two of the ten leading causes of death are infectious diseases (HIV/AIDS and pneumonia/ influenza). The Centers for Disease Control and Prevention (CDC) reports that 160,000 Americans die each year with an infectious disease as the underlying cause of death. This course will introduce you to a variety of communicable diseases, routes of disease transmission, and disease control terminology.

2 In order for a disease to be communicable, the disease must be able to be transmitted from an infected person, animal or an inanimate source to a susceptible host. Transmission can occur directly or indirectly, through an intermediate animal, plant or object. Three elements must be present for successful disease transmission: 1.Agent 2.Environment 3.Host The relationship between the agent, the environment and the host is complex, and is often shown as a triangle (and referred to as the epidemiologic triangle). If any side of the triangle is disrupted, disease transmission will likely cease.

3 Chapter 1: The Agent and Transmission Routes Have you ever had a stomachache, a bad cough or a sore throat and wondered what was causing you feel so bad? Well, it's likely that your symptoms were due to one of many different types of viruses, bacteria, parasites, fungi or other microbes that live in our environment. In this chapter, you will learn about the different characteristics of disease causing agents. Another term for a communicable disease-causing agent is pathogen. Communicable disease agents must be able to do three things: 1. Be present in the environment 2. Find a means of transmission (spread) 3. Survive and multiply The characteristics of an agent play a large role in determining an agent's odds for survival. In turn, these agent-specific characteristics determine how the disease will be distributed in the population and how it will be transmitted. The following characteristics can aid in improving the agent's survival and ability to infect its host. Reservoirs A reservoir is an animal, plant, or substance that harbors a particular organism that can cause disease. A reservoir may or may not have the disease caused by the organism, but serves as a place where the organism can live and multiply until such a time that it is transmitted in some way to the host. An individual who is infected with the organism, and is not showing symptoms, can be a source of infection to others. This individual is referred to as a carrier. For example, rodents act as a reservoir for plague, cattle are often reservoirs for E. coli O157, and chickens, reptiles and amphibians are often reservoirs for Salmonella. During the World Health Organization (WHO) campaign to eradicate smallpox, ring vaccination was successful because humans are the only reservoir for infection by the variola virus (the virus that causes smallpox). When humans around the world were vaccinated, and therefore, not susceptible to infection, the chain of transmission was ended. Agents with multiple reservoirs, such as Salmonella, are very unlikely to be eradicated. Persistence The persistence of the organism in the environment determines where and for how long we can expect to find the agent. For example, anthrax (Bacillus anthracis) produces spores that can live in the environment for many years. In contrast, Campylobacter (one of the most common bacterial causes of diarrheal illness in the United States) prefers a low-oxygen environment, so Campylobacter doesn t survive for very long on surfaces exposed to the air. Latency and Incubation Period Most organisms need some time from the moment they infect a new host until they can become infectious and be spread further. The latent period is the period of time between when the host is infected to when he or she becomes infectious. This period can vary from a few days in the case of influenza, to several weeks for hepatitis A. A closely related concept is the incubation period. The incubation period is the time interval from the time an agent enters the host to the time the agent starts to cause disease. The interplay between these 2 periods is crucial for disease control efforts. For many diseases, the latent period is slightly shorter than the incubation period, meaning that people can be contagious before showing any symptoms of illness and isolating people once they become ill will

4 not necessarily prevent transmission. This is true with many respiratory viruses and with hepatitis A. These characteristics help the agent to continue to survive and move to new hosts. Vector A vector is an organism, such as a mosquito or tick that carries disease-causing microorganisms from one host to another. This can occur by direct inoculation through skin penetration, as with biting insects, or through mechanical transmission where the vector moves the organism from one place to another, as when Shigella is passed from feces to food on flies' feet. Vehicle A vehicle is a contaminated inanimate object that can be an intermediary between a reservoir and a susceptible host. Vehicles can include food, water, objects such as toys or bedding, medical equipment, and the hands of health care workers. An agent s ability to persist in the environment will determine whether the agent can survive on a vehicle(s), and if so, which objects are suitable for transmission. Intermediate Host Some organisms survive in their early developmental stage in another host before infecting the final host. For example, most parasite trematodes (flukes) and cestodes (tapeworms) have indirect lifecycles requiring intermediate hosts. One such example is the pork tapeworm. Pork tapeworm eggs are ingested by a pig, grow into encysted larvae, are consumed by a human, and then the cyst wall is dissolved in the human's intestine, freeing the larvae to attach to the intestinal wall and grow into an adult worm. Factors That Affect the Agent's Ability to Cause Disease 1. Pathogenicity: the ability of an organism to produce disease, that is, signs and symptoms of illness. One way to measure the pathogenicity of an organism is: The total number of people who become ill The number of people who were infected with the organism 2. Virulence: the degree to which the organism causes severe illness. Virulence for a particular agent can vary depending on the organism s subtype or serotype. For example, Salmonella serotype Newport usually causes a diarrheal illness, whereas Salmonella serotype Typhi causes a more severe, systemic illness called typhoid fever. One measure of virulence is the case fatality ratio, which is the number of deaths divided by the total number of people ill.

5 3. Toxicity: some agents produce toxic proteins that elicit an extreme response in the host. An example of this is botulism, which is caused by ingestion of botulinum toxin. The toxin can be produced when food containing the C. botulinum bacteria is mishandled. Botulism is not actually an infection, but rather an intoxication. 4. Infective Dose: the number of organisms necessary to overwhelm the immune system and produce disease. Infective dose varies according to species and strain - some agents require a very high number of organisms to be present in order to overwhelm the host's immune system, other agents only require a few. An organism with a high infective dose, as in the case of Vibrio cholerae, responds well to improved sanitation, because in order for a person to become ill, the person must come in contact with many organisms before they are infected. An organism with a low infective dose, such as Coxiella burnetii, the agent that causes Q fever, can be passed by a few organisms. A person can become infected with Q fever by simply being present at the birth of an animal infected with the organism. Types of Transmission Transmission of an agent to a host can occur by direct or indirect transmission. Direct Transmission Direct transmission is the direct movement of an agent from a reservoir or infected host to a portal of entry in the new host. Examples of direct transmission include: Person-to-Person Transmission: touching, kissing, or sexual activity Droplet Transmission: droplets from a cough or sneeze are projected directly into the air and onto the mucous membranes of a host. Biting (human or animal bites) Note: People can be "carriers" of certain diseases, which means that they do not show symptoms of illness but they can effectively transmit the disease to others. Review the text below to learn more. Carrier or Subclinical State People can be "carriers" of certain diseases, which means that they do not show symptoms of illness but they can effectively transmit the disease to others. Since only a portion of the ill population exhibits symptoms with these types of illnesses, the number of clinically ill is not the same as the total number of people who are actually infected. The proportion of infected people who have symptoms, varies greatly be disease. The carrier state can be either transient, or persistent and chronic. The carrier state can manifest in the following ways: The person is asymptomatic (showing no symptoms) while infected, but is infectious. The person is still in the incubation period for illness, and will develop symptoms at a later date, but is already infectious. The person is infectious after symptoms have resolved. For example, people infected with hepatitis A are infectious for approximately 2 weeks before they develop symptoms (during the incubation period) and continue to be infectious for approximately one week after they develop jaundice (a symptom of hepatitis A). The period of greatest communicability is during the incubation period before symptoms develop. In children, HAV infections often may not result in clinical disease, but they can still transmit infection, especially during diaper changes, as hepatitis A is spread through fecal-oral transmission.

6 Indirect Transmission Indirect transmission occurs when an agent moves from a reservoir or host to another host by means of a living organism or an inanimate object. Examples of indirect transmission include: Vehicle borne Transmission Transmission via a contaminated inanimate object, such as food, water, objects such as toys or bedding, medical devices, etc. The organism may or may not multiply in or on the vehicle. Some common vehicle borne infections are foodborne illness resulting from food prepared by an ill food handler or nosocomial (or hospital acquired) infections that are a result of poor hand-washing among hospital staff. Vector borne Transmission Transmission via a living object (vector). Examples of vector bone transmission include infection with West Nile virus and plague. Indirect transmission through the bite of a flea is the most common route of transmission between plague-infected rodents and humans. Airborne Transmission Transmission via droplet nuclei, or aerosols, that remain airborne for long periods of time and are inhaled. Examples of diseases spread by airborne transmission include measles and tuberculosis. In contrast, droplets from coughs and sneezes are heavy and settle quickly, so transmission of agents contained in droplets is considered direct. Types of Diseases Diseases can be categorized based on the way that they are transmitted. Review the following table to learn about the different ways that communicable diseases can be transmitted (as well as how they can be prevented or controlled). Note: Some diseases fall into more than one of these categories. Transmission Route Fecal-Oral (Yes, that means precisely what you think it means) Hosts (human or animal) infected with these agents shed the agent in their feces. Infection can occur through direct person to person contact and ingestion of contaminated food and water. Such diseases often cause diarrhea and can include giardiasis, shigellosis, E. coli 0157 infection and cholera. Control Methods Fecal-Oral: Control Methods The most important control methods for fecal-oral diseases are adequate hand-washing, and excluding ill people from preparing food until they are no longer contagious. It is also important to ensure that water is clean and comes from a safe source. Some of these diseases, such as hepatitis A and polio are vaccine-preventable. Excreted load, also referred to as shedding, refers to the number of organisms shed in urine or feces, and is an important factor in transmission. It is unrelated to the severity of symptoms.

7 Airborne and Droplet-borne Diseases Many of these diseases produce either respiratory or skin rash symptoms. The difference between airborne and droplet transmission is in the size of the particles expelled. Droplet transmission occurs by droplets greater than five microns. The droplets are sprayed into the air, but usually fall short of three feet. Exposure does not generally occur beyond this range. Diseases spread by droplet transmission include influenza, pertussis, and mumps. Aerosolized droplet nuclei smaller than five microns may remain in the air longer than larger droplets, increasing the range at and length of time during which people can be exposed. Diseases spread by airborne transmission include measles and tuberculosis. Infections like influenza or the common cold can be passed either through respiratory secretions, or by touch contact from mucus membranes. The infective dose and the degree of exposure play a large role in the transmission of these diseases. The force with which particles are expelled also influences their communicability, such as with pertussis. Close contacts are more likely than others to become infected. In addition, host factors like nutrition status also play a large role in determining whether a contact can resist infection. Blood-borne or Bodily Fluid Transmission Diseases in this category can be transmitted through blood, serum, saliva, seminal or vaginal fluid. In addition to direct transmission, however, indirect transmission can occur through contact with fomites exposed to bodily fluid, depending on the hardiness of the organism. Infective dose also plays some role in transmission. For every 100 persons exposed to HIV, one person will be infected (1:100), for every 10 persons exposed to hepatitis C, one persons will be infected (1:10). This is because Hep C is more pathogenic (disease causing) is shed in larger quantities. Some diseases can be spread by all bodily fluids, while some can only be spread by blood. Vector-borne Diseases This set of diseases is transmitted through another organism called a vector, since it uses a transporter to get from one place to another, (a "Light Rail" for microbes). Vectors are often insects. This method of transmission eliminates the need for multiple organisms to scatter throughout the environment, and is carried straight to the host. Some organisms go through a developmental stage in the vector, and others do not. In the infective stage, often the organism can continue multiplying and being transmitted for the remaining life of the vector. Often the organisms are transmitted by bite. Airborne and Droplet-borne Diseases: Control Methods Control of droplet and airborne infections is difficult, but covering the mouth in the crook of the arm when coughing, and washing hands after coughing, sneezing, or after contact with mucus membranes, and avoiding people who are sick, a practice known as social distancing, can prevent or reduce transmission. Some of these diseases can be prevented with vaccination, such as measles, smallpox, chickenpox, pertussis, diphtheria, influenza, etc. Review the CDC guidelines for respiratory hygiene in healthcare settings. Blood-borne or Bodily Fluid Transmission: Control Methods Eliminating or reducing exchange of blood and bodily fluids eliminates or reduces the risk of transmission of blood and fluid-borne diseases. This can include practices such as not sharing toothbrushes, razors, needles or injection equipment. Sexual transmission is trickier to control. Sexual transmission can be controlled by either abstinence, or sex with a barrier, such as a latex condom. Vector-borne Diseases: Control Methods The best method of prevention and control is often to eliminate or reduce the numbers of the vector, such as draining or eliminating standing water, or encouraging citizens to reduce potential breeding sites (as is recommended for mosquito-borne illness). In addition, it is sometimes possible to limit the exposure of people to the vector, such as by covering exposed skin at dusk and dawn, the feeding times of Culex mosquitos, or wearing bug repellant.

8 Diseases are also categorized in other ways, such as by the types of reservoirs where the causative agents are found, by the strategies used to prevent them, or by the types of illnesses that they can cause. Some examples of these include: Zoonotic Diseases Zoonotic diseases are diseases caused by agents with animal reservoirs. Some of these diseases are transmitted through a vector, such as plague, and others are not, such as anthrax. Humans are "accidental hosts" in this cycle, meaning they are not natural reservoirs for the agents in question but are incidentally infected when they have contact with those reservoirs. Other zoonotic diseases can be transmitted through contamination of food or water by animal feces (e.g. E. coli O157), contact with urine or animal hides (e.g. hantavirus or anthrax), or animal bites (e.g. rabies). Food-borne Diseases Foodborne illness occurs through consumption of contaminated food. Food contamination can be the result of many factors including: food that was prepared by an ill food handler, food that was not cooked thoroughly before consumption (such as raw oysters or undercooked chicken), food that was held at improper temperatures allowing toxins to be produced, or preparing food on contaminated surfaces. Foodborne illness can be an intoxication, poisoning by toxins (e.g. Staphyloccus aureus toxin or Clostridium botulinum toxin), or infection with bacteria, viruses, or parasites (e.g. Campylobacter, norovirus, or Cyclospora). Food-borne diseases can be intertwined with water-related diseases, since food preparation often involves water. Water-borne Diseases These diseases are passed through contact with, or ingestion of, contaminated water. Cryptosporidiosis and giardiasis can occur naturally in Colorado through the ingestion of contaminated water. Wound infections with Vibrio species can occur among people with wounds expsosed to seawater. In addition, water contaminated with feces can harbor organisms that contaminate food sources, such as raw shellfish, which can pass along the hepatitis A virus. Disasters, such as Hurricane Katrina, can cause widespread contamination of water by sewage, and a proliferation of water-related diseases not typically found under other circumstances. Vaccine-Preventable Diseases This refers to the group of diseases for which a key prevention strategy is vaccination. This group includes diseases that are spread through many different routes of transmission, including: airborne transmission (e.g. measles), droplet transmission (e.g. pertussis, influenza), fecal-oral transmission (e.g. hepatitis A, polio), and blood-borne/body fluid transmission (e.g. hepatitis B).

9 Chapter 2: The Host and the Environment The Host The host is an organism that is capable of being infected or affected by a disease agent. In some circumstances, an agent and its host can live together in reasonable harmony, for example humans and herpes simplex virus. In others, the agent causes the host to become very ill or possibly die, such as with plague. In the human host, the agent, or pathogen, causes disease by either disrupting a vital body process or stimulating the immune system to mount a defensive reaction. An immune response against a pathogen can lead to a variety of symptoms. The likelihood that an individual will become infected and develop illness depends on a variety of host factors, or factors that are specific to that individual including the host s susceptibility to the disease in question and the host s overall resistance. Host Factors Affecting Exposure There are many behavioral and sociodemographic factors that may affect whether a host is more or less likely to be exposed to an agent in the first place. Some of these include things such as: Occupation Travel Eating habits Socio-economic status When performing epidemiologic investigations, disease investigators sometimes find a correlation between the amount of agent to which the host is exposed and the strength of the illness, or the likelihood of becoming ill. This relationship is known as dose-response. Dose-response can be very apparent in certain kinds of foodborne illness (the more you eat, the more likely you are to become ill). Susceptibility Many factors such as age, gender, and conditions such as pregnancy can affect a person s ability to fight off, or their resistance to, infection. Before we get to all those factors, one key host factor is the concept of susceptibility. A person is susceptible to a disease if he or she is not immune to that disease. Agents can only infect people who are susceptible. For example, persons who have been vaccinated against pertussis or have already had pertussis, cannot catch pertussis or pass it to others. Individuals who have not previously had pertussis, or who have not been vaccinated recently, are susceptible to infection. Immunity Immunity to infection can occur in a number of ways: Passive Immunity The host acquires antibodies to the agent from another source. Babies acquire maternal antibodies in utero and through breast milk. Passive immunity is also conferred by inoculation with immune globulin. Protection from disease is generally temporary. Active Immunity Active immunity entails either the elicitation of an immune response through intentional inoculation with the agent by vaccination, or by contracting the infection. Someone with active immunity will be able to mount an immune response when exposed to an agent. Herd Immunity Both passive and active immunity contribute to the overall herd immunity of a population. When many persons in a population are immune to an infection, they break the chain of infection by not transmitting it to persons with no immunity.

10 Another important concept is that for some diseases, immunity may wane over time, necessitating booster doses of vaccine in order to remain immune. Some examples of this are tetanus, where adults are advised to receive booster shots every 10 years, and pertussis, where immunity from childhood vaccinations wanes in the adolescent years. Resistance In a population of susceptible people who are exposed to a disease, certain people are more likely to become ill than others. This is due to each individual's resistance. Factors that affect a person's resistance to disease include: Physical Defense Mechanisms The human body has developed many physical defense mechanisms to protect against disease. Our skin is an effective barrier against infection, as are mucus-secreting membranes and the inflammatory response that sends blood and phagocytes to a cut, blister or other area of inoculation. If these mechanisms are damaged, a person increases his/her risk for infection. Factors Affecting Overall Immune System Functioning: Nutritional status Chronic medical conditions/immunosuppressive conditions Immunosuppressive drugs Age Gender Pregnancy Genetics The Environment Environmental factors have a large impact on the disease transmission relationship between the agent and the host. Environmental factors include living conditions, climate, societal norms, cultural practices, personal resources, education, biological organisms present, and more. For example, factors such as temperature, humidity, and wind can affect the transmission potential and the survival of pathogenic organisms. These factors can also affect the stress level placed on people, thus increasing a person's susceptibility to disease. Other examples of how the environment can impact the transmission of disease include: Methicillin resistant Staphylococcus aureus (MRSA) MRSA is transmitted from person to person through direct skin contact and contact with contaminated objects. During the past few years, correctional facilities have seen an increase in MRSA infections, and even some outbreaks among inmates. Several reasons for the higher rates of MRSA infections in correctional facilities include crowding, decreased access to soap or towels, and relatively high rates of pre-existing medical conditions among inmates. This is an example of how environmental factors particular to a correctional setting affect disease transmission. E. coli 0157 E. coli 0157 has a clear seasonal distribution, with cases peaking each year during the summer months. Several potential reasons for this include increased prevalence of E. coli O157 in animals (the reservoir) during warmer months, more people coming together for picnics and other gatherings where meat may not be thoroughly cooked, and warmer temperatures allowing for increased bacterial multiplication in contaminated foods that are not promptly refrigerated. Environmental factors are taken into consideration by epidemiologists when they collect information based on person, place, and time. These factors help to answer questions such as: Who is getting sick? Where are they getting sick?

11 When? Epidemiologists collect person, place and time information in order to gather clues about the agent (incubation period), the host (age or sex distribution) and the environmental factors at play (seasonality, location) You will learn more about disease investigation and the study of epidemiology in the second online course, The Basics of Public Health Surveillance. Chapter 3: General Communicable Disease Concepts Infection Timeline Communicable diseases often follow along an epidemic timeline involving the incubation period and the infectious period. These two terms are defined below using influenza and hepatitis A as examples: Incubation Period: Time of infection to clinical disease Infectious Period: Period during which agent can be transmitted. This can vary depending on the agent. As depicted in the graph above, the infectious period and the incubation period vary to a large degree from agent to agent and need to be considered when planning control measures for each agent. Scope of Disease The degree to which a disease exists in a community or area defines whether it is a(n): Endemic Endemic refers to the usual level of disease in a population, which can be either a high or low rate. Chlamydia, which causes pelvic inflammatory disease, while sometimes surfacing as an epidemic, is often present in the population, particularly among sex workers. Epidemic An epidemic is occurring when the amount of disease in a particular population in a particular time frame is greater than expected. The terms epidemic and outbreak can be used interchangeably, although outbreak is sometimes preferred in working with the public because the connotation does not seem to be as frightening.

12 This graph shows the number of cases of Salmonella Newport reported in Colorado from In July 2002 and January 2003, the number of reported cases exceeded historical averages and outbreak investigations were conducted. Pandemic A pandemic is an epidemic that crosses the borders of multiple countries at the same time. Three influenza pandemics occured in the 20th century , , and Currently, the H5N1 avian influenza virus is being monitored to determine if this virus is going to become transmitted easily from person-to-person. As an avian disease, the H5N1 virus has already spread to multiple countries. This disease will not be defined as a pandemic until it becomes easily transmitted from person-to-person and spreads to multiple countries. Types of Epidemics (Outbreaks) Different agents and different exposures result in different types of outbreaks. An epidemic curve, which shows number of cases over time, looks different for each type. Point Source Outbreak A point source outbreak results from a single exposure, such as a contaminated batch of meat. It appears as a tight clustering over time. The upslope is sudden, and the downslope tapers. Onsets times/dates for most cases will be within the span of one incubation period for the disease. In point source outbreaks as in other types, there can be secondary waves of infection, as the original infected persons spread it to others, such as in a hepatitis A outbreak.

13 Continuing Common Source There can be a continuing common source, as with a contaminated well. If the source is removed, the down-slope will be sharp, if not it will taper as the number of susceptible individuals declines.. The rise in the curve will plateau rather than demonstrate a peak. *The cholera outbreak that made John Snow famous would have looked something like this, except with a sharp downslope when he removed the pump handles. Propagated Outbreak This type of outbreak demonstrates transmission from host to host, such as in chickenpox. There may be several generation periods for the agent. It demonstrates a gradual upslope as the disease is transmitted person-to-person, and then a sharp down-slope as the agent runs out of susceptible hosts. Diagnosis To diagnose a disease, various tests can be performed depending on the type of agent. Many organisms can be diagnosed using several different tests. Some of the more common tests are listed below: Cultures Microbiological cultures can identify types of bacteria, such as Staphylococcus or Streptococcus. In a culture, a growth medium is provided for a particular agent so that the agent can reproduce and be identified in a laboratory setting. Conditions of public health concern that are frequently diagnosed by culture include Salmonella, Streptococcus pneumoniae, and Neisseria meningitidis (the organism that causes meningococcal disease). Serology Certain agents cannot be cultured, including most viruses. Serology involves detecting the antibodies against an infectious agent in the patient's blood. If a person has the antibodies to a

14 specific virus in their blood, they have been exposed to, and are potentially infected with the virus in question. Conditions of public health concern that are frequently diagnosed by serology include: hepatitis A, B and C, rubella and measles. Polymerase Chain Reaction (PCR) A more recent development is direct detection of viral proteins and/or bacterial DNA in human blood or secretions. This can be done by PCR (polymerase chain reaction), involving the amplification of an agent's genetic material and its subsequent detection with anti-dna probes. In the current political climate, with emphasis placed on the possibility of biological warfare, understanding differences between the presentation of two similar diseases has become more critical (such as between smallpox and chickenpox, or tularemia and plague). Recognizing the symptoms of Category A or B agents, which may not be commonly seen, depending on the setting, is of prime importance in stopping transmission early. Since control measures are highly specific and must be tailored to the agent, it is very important to identify the agent causing disease so that correct and specific control measures can be implemented. Chapter 4: Prevention and Control The goal of communicable disease epidemiology is to enhance disease prevention and control to decrease the burden of illness. The most important feature of both prevention and control is to interrupt the chain of transmission. For different diseases, this process requires different measures which can range from washing hands, to turning over trash cans to prevent water from collecting (which destroys vector breeding sites), to vaccinating humans and/or animal reservoirs, to changing the pattern of intimate human behavior. Control measures are highly dependent on the agent in question. Public health professionals must take many factors in to consideration, including the organism s reservoir, routes of transmission, the prevalence of the disease, the presence of a carrier state, and the incubation period. Using our disease "bugs" as an example, specific disease control measures include: Pertussis Since pertussis is spread via direct person-to-person transmission, disease control should focus on cough etiquette, exclusion from work or school, and antibiotic therapy. The primary disease control strategy is vaccination. Pertussis does not have an animal reservoir, that is, it lives only in humans, so all control strategies focus on people. Salmonella To control the spread of Salmonella, epidemiologists recommend several options. These include hand-washing (after using the bathroom, after animal contact, and before handling food), excluding infected food handlers from work, encouraging children and the elderly to avoid animals that are reservoirs (animals in petting zoos, chicks and reptiles, in particular), proper food handling and cooking food to a proper temperature. These recommendations take into account that people of different age groups are differently affected by Salmonella infections. West Nile Virus To control the spread of West Nile Virus, people should protect themselves by covering exposed skin with clothing and wearing mosquito repellent that contains DEET. It is also important to eliminate mosquito breeding sites by removing stagnant, standing water by draining rain barrels, bird-baths, swimming-pool covers, eavestroughs, flowerpots, and planters. These strategies take into account control of the vector (the mosquito), but not control of the reservoir (birds), which would be impractical. They also target environmental factors such as host behaviors that decrease opportunities for transmission.

15 Prevention Measures Many infectious diseases can be prevented through simple and inexpensive methods: Wash Your Hands Wash hands before, during and after preparing food, before eating, after using the bathroom or changing diapers, and after handling animals or animal waste. Routinely Clean and Disinfect Surfaces Cleaning with soap and water removes dirt and most germs. Using a disinfectant kills additional germs. It is important to thoroughly clean areas where germs are likely to be transmitted, such as the kitchen and bathroom. Handle and Prepare Food Safely Buy and refrigerate perishable foods quickly. Store food properly. Don t allow juices from meat, seafood, and poultry or eggs to drip on other foods. Wash hands and kitchen surfaces and utensils while preparing food. Wash raw fruits and vegetables. Don t eat raw eggs. use a meat thermometer when cooking meat and poultry.use different dishes for raw foods and cooked foods. Keep cold foods cold and hot foods hot. Don t leave leftovers out longer than two hours. Get Immunized Children, adolescents and adults need immunizations. Make sure the members of your family get the right vaccines at the right time. Keep immunization records for the whole family. Visit Colorado's Immunization web site to learn more. Use Antibiotics Properly Unnecessary antibiotics can be harmful and, if misused, can cause bacteria to become resistant to treatment. Antibiotics don t work against viruses like colds and flu. Use antibiotics exactly as prescribed by your provider. Summary In summary, there are many types of communicable diseases that threaten the health of Colorado communities. In order to be communicable, a disease must be present in the environment, find a means of transmission and survive and multiply in a host. Simple prevention measures such as vaccination and hand washing can interrupt disease transmission in order to keep members of our communities healthy. For additional information, review the course "Resources" page. This document provides a list of websites and other useful information related to disease surveillance in the state of Colorado. To complete this course, you must take the final exam online.