1. MICR 420 Emerging and Re-Emerging Infectious Diseases Lecture 2: Epidemiology Dr. Nancy McQueen & Dr. Edith Porter

2. Overview Concepts of epidemiology The cycle of microbial disease Reservoirs of infection Transmission Portals of entry Portals of exit Nosocomial infections Epidemiology of fear

3. What is Epidemiology? As told by CDC … It seems that one of their scientists, on first arriving at CDC from a clinical practice, found himself somewhat unsure of what epidemiology was all about, so he sought an answer down the street at Emory University. The first person he asked was a medical student, who told him that epidemiology was "the worst taught course in medical school." The second, a clinical faculty member, told him epidemiology was "the science of making the obvious obscure." Finally, knowing that statistics are important to epidemiology, he asked a statistician, who told him that epidemiology is "the science of long division" and provided him with a summary equation. Giving up on finding a real answer, he returned to CDC. On the way, however, he decided to try one more time. He stopped a native Atlantan who told him that epidemiology was "the study of skin diseases.”

4. What is Epidemiology really? Study—Epidemiology is the basic science of public health. It's a highly quantitative discipline based on principles of statistics and research methodologies. Distribution—Epidemiologists study the distribution of frequencies and patterns of health events within groups in a population. To do this, they use descriptive epidemiology, which characterizes health events in terms of time, place, and person. Determinants—Epidemiologists also attempt to search for causes or factors that are associated with increased risk or probability of disease. This type of epidemiology, where we move from questions of "who," "what," "where," and "when" and start trying to answer "how" and "why," is referred to as analytical epidemiology.

5. What is Epidemiology really? Health-related states—Epidemiology as it is practiced today is applied to the whole spectrum of health-related events, which includes chronic disease, environmental problems, behavioral problems, and injuries in addition to infectious disease. Populations—One of the most important distinguishing characteristics of epidemiology is that it deals with groups of people rather than with individual patients. Control—Epidemiological data steers public health decision making and aids in developing and evaluating interventions to control and prevent health problems. This is the primary function of applied, or field, epidemiology.

6. History of Epidemiology Hippocrates in 460 – 377 B.C. Malaria associated with swampy environments Edward Jenner in late 18 th century Cow pox protects from small pox First vaccination Ignaz Semmelweis Childbed fever (puerperal sepsis) John Snow Cholera outbreaks in London Florence Nightingale Epidemic typhus in mid 19th century

7. Ignaz Semmelweis and Puerperal Sepsis Mandatory hand washing introduced

8. John Snow and Cholera Cholera epidemics in London 1846 – 1849 Snow analyzed the death records and interviewed survivors Created map Most individuals who died of cholera used water from Broad street pump Survivors did not drink water but beer instead or used another pump Identified the Broad street water pump as likely source After closing this pump number of cholera cases dropped significantly

9. Florence Nightingale and Epidemic Typhus Recorded statistics on epidemic typhus in English civilian and military populations Published a 1000 page report in 1858 Statistically linked disease and death with poor food and unsanitary conditions Novel graph: coxcomb chart or polar area diagram chart Fixed angle and variable radii Resulted in reforms in the British Army Nightingale became the first female member of the Statistical Society

10. Investigation Types in Epidemiology Experimental Epidemiologist is in control of the circumstances at the beginning of the study Begins with a hypothesis Prospective study that usually involves controls Example: Semmelweis’ study; vaccine efficacy trials Observational Epidemiologist is not in control of the circumstances at the beginning of the study Descriptive Collect data about affected individuals, the places and the periods in which disease occurred (Who? Where? When?) Typically retrospective E.g. Snow’s study Analytical Analyzes a particular disease to determine its probable cause (How? Why?) Case control method – look for factors that might have preceded the disease Cohort method – study of two populations, one having had contact with the disease agent and the other that has not E.g., Nightingale’s study

11. Case Reporting Health care workers are required to report specified diseases to local, state, and national offices

12. Centers for Disease Control and Prevention (CDC) Branch of the U.S. Public Health Service Collects and analyzes epidemiological information in the U.S. Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov Morbidity: incidence of a specific notifiable disease Mortality: deaths from notifiable diseases Morbidity rate: number of people affected/total population in a given time period Mortality rate: number of deaths from a disease/total population in a given time

13. Notifiable Diseases Reported to the CDC To detect reemergence of disease and be able to respond early List includes AIDS Anthrax Botulism Cholera Cryptosporidiosis Diptheria Ehrlichiosis Encephalitis (arboviral) Enterohemorrhagic E. coli Hanta virus Hepatitis, viral Malaria Meningococcal disease Pertussis Streptococcal diseases, invasive Group A Tuberculosis VISA, VRSA

14. Frequency and Distribution of Disease Sporadic disease Disease that occurs occasionally in a population at irregular intervals Endemic disease Disease continually present in a population at low frequency and a steady level Epidemic disease High frequency over short time Disease acquired by many hosts in a given area in a short time Disease with sudden increase of morbidity (illness rate) and mortality (death rate) above the normal level Common source versus propagated Pandemic disease Worldwide epidemic

15. Classification of diseases by frequency and distribution

16. Difference between Endemic and Epidemic Disease Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

17. Source and Spread of Major Epidemics Common-source epidemic Disease spread from one source Little transmission from infected (e.g., food poisoning) Propagated epidemic Disease continuously transmitted from infected Higher numbers, longer- lasting epidemic (e.g. flu) Propagated or

18. Herd Immunity Large fraction of a population is immune to a given disease, and it is difficult for the disease to spread (proportion immune individuals needed depends upon type of infection)

19. Cycle of Microbial Disease Reservoir Transmission Portal of entry Portal of exit Disease

20. Reservoirs of Infection Where do you get the infection from? Site in nature where microbes survive (and possibly multiply) Continual sources of infection Humans Small pox, gonorrhea Active carriers: acutely ill Healthy carriers: no symptoms inapparent infections or latent diseases Example: Typhoid Mary Animals Zoonoses Rabies, Lyme disease Fomite Soil, water Botulism, tetanus Living reservoirs Non-living reservoirs

21. Transmission How do you get the infection? Direct Requires close association between infected and susceptible host Person – to – person Horizontal  Fecal-oral  Droplet Vertical  Mother – to – child Animal bites Indirect Vehicle (fomites, water) Airborne (aerosols) Vector

22. Epidemiological Vectors Arthropods Invertebrates with jointed appendages Ticks, flies, mosquitoes, fleas Mechanical vector Biological vector Microbe proliferates in arthropod Necessary component in the life cycle of the microbe Sometimes transovarial transmission Tick Borrelia burgdorferi Lyme Disease: Skin manifestation Plague Malaria Trypanosomiasis

23. Portals of Entry and Exit Respiratory tract Intestinal tract Urinary tract Genital tract Skin Blood Mucous membranes

24. Nosocomial Infections Acquired by compromised hosts during a hospital stay 5-15% of all hospital patients 50% of all major hospital complications At 2 – 4 million admissions/year estimated 20,000 – 40,000 deaths per year in the US

25. Body Site Distribution of Nosocomial Infections

26. Factors Contributing to Nosocomial Infections Patient population is immune comprised Misuse of antibiotics with development of antibiotic resistant strains Medical devices as new portals of entry Hospital staff as reservoir

27. Control Measures against Nosocomial Infections Appropriate use of antibiotics Safe and effective decontamination and sterilization Staff hygiene Hand washing Screening of all hospital patients?

28. Epidemiology of Fear Fear with epidemic proportions Example: West Nile Virus (CDC national data) 2006: 5000 infections with 180 deaths 2007: 3600 infections with 121 deaths 2008: 1356 infections with 44 deaths 2009: 663 infections with 30 deaths Not a public threat!

29. Take Home Message Epidemiological classification of disease is based on frequency and distribution as sporadic, endemic, epidemic, and pandemic. The cycle of microbial disease includes reservoir, transmission, portal of entry and portal of exit. Transmission may be direct from person to person or indirect through an intermediate agent such as a fomite or a vector. Nosocomial infections are hospital acquired infections often caused by multidrugresistant microorganisms.

30. Additional Resources The Microbial Challenge, by Krasner, ASM Press, Washington DC, 2002. Brock Biology of Microorganisms, by Madigan and Martinko, Pearson Prentice Hall, Upper Saddle River, NJ, 11 th ed, 2006. Tortora et al., Chapter 14 http://www.cdc.gov/excite/classroom/intro_epi.htm http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/J/JohnSnow.gif http://www.gazellebookservices.co.uk/Military/originals/Military/19th%20Century/Flore nce%20Nightingale%20and%20the%20Crimean%20War.jpg http://www.gazellebookservices.co.uk/Military/originals/Military/19th%20Century/Flore nce%20Nightingale%20and%20the%20Crimean%20War.jpg.http://www.britannica.com/eb/art-70822 http://www.cdc.gov/ncphi/disss/nndss/phs/files/NNDSS_event_code_list_January_20 10.pdf http://www.cdc.gov/ncphi/disss/nndss/phs/files/NNDSS_event_code_list_January_20 10.pdf