1. EPIDEMIOLOGY AND PUBLIC HEALTH Dr. Mohammad Shakeeb,MD Specialist in clinical pathology/microbiology and immunology

2. EPIDEMIOLOGY

3.  Introduction An epidemiologist studies the factors that determine the frequency, distribution, and determinants of diseases in human populations. With respect to infectious diseases, these factors include: the characteristics of various pathogens Susceptibility of different human populations Locations (reservoirs) where pathogens are lurking Various ways in which infectious diseases are transmitted

4. EPIDEMIOLOGY epidemiologists are concerned with: Who becomes infected? What pathogens are causing the infections? Where do the pathogens come from? When do certain diseases occur? Why do some diseases occur in certain places but not in others? How are pathogens transmitted? Do some diseases occur only at certain times of the year? If so, why?

5. Epidemiologists also develop ways to prevent, control, or eradicate diseases in populations.  Epidemiologic Terminology  Communicable and Contagious Diseases  Zoonotic Diseases  Incidence and Morbidity Rate  Prevalence  Mortality Rate  Sporadic Diseases  Endemic Diseases  Epidemic Diseases  Pandemic Diseases

6.  Communicable and Contagious Diseases Communicable disease: infectious disease is transmissible from one human to another (i.e., person to person). Contagious disease :is defined as a communicable disease that is easily transmitted from one person to another.  Zoonotic Diseases Infectious diseases that humans acquire from animal sources,  Incidence and Morbidity Rate The incidence of a particular disease is defined as the number of new cases of that disease in a defined population during a specific time period.

7. morbidity rate expressed as the number of new cases of a particular disease that occurred during a specified time period per a specifically defined population (usually per 1,000, 10,000, or 100,000 population).  Prevalence The period prevalence of a particular disease is the number of cases of the disease existing in a given population during a specific time period. The point prevalence of a particular disease is the number of cases of the disease existing in a given population at a particular moment in time.

8.  Mortality Rate The mortality rate (also known as the death rate) is the ratio of the number of people who died of a particular disease during a specified time period per a specified population (usually per 1,000, 10,000, or 100,000 population).  Sporadic Diseases A sporadic disease is a disease that occurs only occasionally (sporadically) within the population of a particular geographic area. Example : In the United States, sporadic diseases include botulism, cholera, gas gangrene, plague, tetanus, and typhoid fever.

9. they are kept under control as a result of immunization programs and sanitary conditions.  Endemic Diseases Endemic diseases are diseases that are always present within the population of a particular geographic area. The number of cases of the disease may fluctuate over time, but the disease never dies out completely. Endemic infectious diseases of the United States include: tuberculosis (TB), sexually transmitted diseases (STDs) like gonorrhea and syphilis and viral diseases such as the common cold, influenza.

10.  Epidemic Diseases An epidemic (or outbreak) is defined as a greater than usual number of cases of a disease in a particular region, usually occurring within a relatively short period of time. Read the following examples about the epidemics that have occurred in the United States within the past 35 years (you will be asked about this topic in the exam).

11. 1976. An epidemic of a respiratory disease (Legionnaires’ disease or legionellosis) 1992–1993. An epidemic involving Escherichia coli O157:H7-contaminated hamburger meat occurred in the Pacific northwest. 1993. An epidemic of hantavirus pulmonary syndrome 1993. An epidemic of cryptosporidiosis (a diarrheal disease) occurred in Milwaukee, Wisconsin.

12. 2002. An epidemic of West Nile virus (WNV) infections occurred throughout the United States. Waterborne disease outbreaks. Foodborne disease outbreaks.

13. Epidemics usually follow a specific pattern, in which the number of cases of a disease increases to a maximum and then decreases rapidly. Epidemics may occur in communities that have not been previously exposed to a particular pathogen. In communities in which normal sanitation practices are relaxed, allowing fecal contamination of water supplies and food, epidemics of typhoid fever, cholera, giardiasis and dysentery often occur. Visitors to these communities should be aware that they are especially susceptible to these diseases.

14. Influenza (“flu”) epidemics occur in many areas during certain times of the year and involve most of the population because the immunity developed in prior years is usually temporary. Epidemics of influenza cause approximately 20,000 deaths per year in the United States. Ebola virus has caused several epidemics of hemorrhagic fever in Africa. The source of the virus is not yet known. In a hospital setting, a relatively small number of infected patients can constitute an epidemic situation must be brought to the attention of the Hospital Infection Control Committee.

15.  Pandemic Diseases A pandemic disease is a disease that is occurring in epidemic proportions in many countries simultaneously—sometimes worldwide. The 1918 Spanish flu pandemic was the most devastating pandemic of the 20th century. That pandemic killed more than 20 million people worldwide, including 500,000 in the United States. Almost every nation on Earth was affected.

16. infectious diseases are responsible for approximately half the deaths that occur in developing countries. approximately half of those are caused by three infectious diseases: human immunodeficiency virus/ acquired immunodeficiency syndrome (HIV/AIDS). Tuberculosis. Malaria. Read about these pandemics from your textbook Collectively, HIV/AIDS, TB, and malaria cause more than 300 million illnesses and more than 5 million deaths per year.

17. INTERACTIONS AMONG PATHOGENS, HOSTS,AND ENVIRONMENTS

18. Whether or not an infectious disease occurs depends on: 1.Pathogen factors. 2.Host (i.e., the person who may become infected)factors. 3.Environmental factors.

19. Pathogen factors includes The virulence of the pathogen, a portal of entry, The number of organisms that enter the body. Host factors include : person’s health status person’s nutritional status Age lifestyle [behavior], Socioeconomic level Occupation Travel immune status

20. Environmental factors includes: geographic location Climate Heat,Cold,Humidity season of the year. Availability of appropriate reservoirs, intermediate hosts, and vectors. Sanitary and housing conditions. adequate waste disposal. adequate healthcare

21. CHAIN OF INFECTION

22. There are six components in the infectious disease process (also known as the chain of infection). The six components in the chain of infection are : A pathogen. A reservoir of infection. A portal of exit. A mode of transmission. A portal of entry. A susceptible host.

24. STRATEGIES FOR BREAKING THE CHAIN OF INFECTION

25. measures must be taken to break the chain of infection at some point (link) in the chain : Eliminate or contain the reservoirs of pathogens or curtail the persistence of a pathogen at the source. Prevent contact with infectious substances from exit pathways. Eliminate means of transmission. Block exposure to entry pathways. Reduce or eliminate the susceptibility of potential hosts.

26. Some of the specific methods of breaking the chain of infection are: Practice effective hand hygiene procedures Maintain good nutrition and adequate rest and reduce stress Obtain immunizations against common pathogens Practice insect and rodent control measures Practice proper patient isolation procedures Ensure proper decontamination of surfaces and medical instruments Dispose of sharps and infectious waste properly Use gloves, gowns, masks, respirators, and other personal protective equipment, whenever appropriate to do so Use needle safety devices during blood collection

27. RESERVOIRS OF INFECTION

28. A reservoir is any site where the pathogen can multiply or merely survive until it is transferred to a host. Reservoirs may be living hosts or inanimate objects or materials.

29. RESERVOIRS OF INFECTION Living Reservoirs  Human Carriers  Animals  Arthropods Nonliving Reservoirs

30. RESERVOIRS OF INFECTION  Human Carriers A carrier is a person who is colonized with a particular pathogen, but the pathogen is not currently causing disease in that person. The pathogen can be transmitted from the carrier to others, who may then become ill. Passive carriers carry the pathogen without ever having had the disease. An incubatory carrier is a person who is capable of transmitting a pathogen during the incubation period of a particular infectious disease.

31. Convalescent carriers harbor and can transmit a particular pathogen while recovering from an infectious disease (i.e., during the convalescence period). Active carriers have completely recovered from the disease, but continue to harbor the pathogen indefinitely. Respiratory secretions or feces are usually the vehicles by which the pathogen is transferred. Directly or indirectly (through food or water ). Staphylococcal and streptococcal infections as well as in the spread of hepatitis, diphtheria, dysentery, meningitis, and STDs.

32.  Animals Zoonotic diseases (zoonoses): are infectious diseases that humans acquire from animal sources.  Arthropods Many different types of arthropods serve as reservoirs of infection, including insects (e.g., mosquitoes, biting flies, lice, fleas), and arachnids (e.g., mites, ticks). When involved in the transmission of infectious diseases, these arthropods are referred to as vectors.

33. The arthropod vector may first take a blood meal from an infected person or animal and then transfer the pathogen to a healthy individual.

34. Examples of Zoonotic Diseases

35. CATEGORY DISEASE PATHOGEN ANIMAL RESERVOIR(S) MODE OF TRANSMISSION

37.  Nonliving Reservoirs Nonliving or inanimate reservoirs of infection include air, soil, dust, food, milk, water, and fomites. Respiratory viruses----transmitted through the air on droplets of respiratory tract secretions. fungal respiratory diseases (e.g., histoplasmosis) are frequently transferred by dust containing yeasts or spores. Soil contains the spores of the Clostridium species that cause tetanus, botulism, and gas gangrene.

39. MODES OF TRANSMISSION The five principal modes by which transmission of pathogens occur are contact (either direct or indirect contact), droplet, airborne, vehicular, and vector transmission.