Epidemiology - Introduction

1. Epidemiology - Introduction Study of patterns, distribution of disease (or other events) • Cause/transmission • Develop strategies for prevention Epidemiologists, “health detectives” Dr. Ignaz Semmelweis, Vienna (19th century), Puerperal fever

2. Epidemiology • Principles of Epidemiology • Epidemiological studies • Infectious Disease Surveillance • Trends in Disease • Nosocomial Infections

3. Principles of Epidemiology • Rate of Disease in a population • Reservoirs of Infection • Transmission • Influential Factors

4. Rates of Disease in a Population Endemic - disease constantly present in a particular geographic area Epidemic - disease with an unusually high occurrence Pandemic - worldwide severe epidemic Morbidity - illness (morbidity rate) Rate vs. Absolute number Mortality - death (mortality rate)

5. Outbreak– cluster of cases occurring during a brief time interval and affecting a specific population.

6. Transmission Spread/prevention of disease Natural habitat Reservoir

7. Transmission Natural habitat Reservoir Reservoirs of infectious agents • Human reservoirs Symptomatic ex. cold virus Asymptomatic carriers ex. Neis. gon., Staph. aureus **humans only reservoir - easiest to control** • Non-human animal reservoirs poultry - Salmonella, Campylobacter

9. Transmission Natural habitat Reservoir Reservoirs of infectious agents • Human reservoirs Symptomatic ex. cold virus Asymptomatic carriers ex. Neis. gon, Staph. aureus **humans only reservoir - easiest to control** • Non-human animal reservoirs poultry - Salmonella, Campylobacter rodents - Yersinia pestis bats and racoons - rabies virus

11. Transmission Natural habitat Reservoir Reservoirs of infectious agents • Human reservoirs Symptomatic ex. cold virus Asymptomatic carriers ex. Neis. gon, Staph. aureus **humans only reservoir - easiest to control** • Non-human animal reservoirs poultry - Salmonella, Campylobacter rodents - Yersinia pestis bats and racoons - rabies virus **animal reservoir - difficult to control**

12. Transmission Natural habitat Reservoir Reservoirs of infectious agents • Human reservoirs Symptomatic ex. cold virus Asymptomatic carriers ex. Neis. gon, Staph. aureus **humans only reservoir - easiest to control** • Non-human animal reservoirs poultry - Salmonella, Campylobacter rodents - Yersinia pestis bats and racoons - rabies virus **animal reservoir - difficult to control** - diseases of animals transmitted to humans Zoonoses/zoonotic diseases • Environmental reservoirs soil - Clostridium species

13. Transmission Natural habitat Reservoir Transmission Horizontal (person to person) Vertical (mother to fetus) • contact direct contact indirect contact fomite • inanimate object, such as clothing, doorknob and so on Importance of hand washing droplet Large microbe-laden respiratory droplets generally fall to the ground on farther than 3 feet. Importance of covering mouth when cough or sneeze

15. Transmission horizontal Transmission Natural habitat vertical Reservoir • contact direct contact indirect contact fomite - inanimate object droplet • food and water • air very difficult to control • vectors arthropods flea - Yersinia pestis mosquito - Plasmodium species (malaria)

16. flea flea rodent rodent flea “Black Death” (Plague) - Yersinia pestis Killed 1/4 of the population of Europe between 1346 - 1350; 75% of the population in some cities. Bubonic plague • Flea transmits Y. pestis to a human • Bacterium is carried to a lymph node. • Bubo develops within days • Y. pestis begins interfering with the inflammatory response - “arms itself” • Multiplying bacteria spill into bloodstream (septicemic plague); endotoxin  shock, DIC • 50 - 75% mortality (if untreated)

17. Influential Factors • Dose There are few if any infections for which immunity is absolute. • Incubation Period • Population Characteristics Immunity, General Health, Age, Gender, Genetic Background

18. Epidemiological studies • Descriptive studies Risk factors Person Place Time • Analytical studies • Experimental Studies Which risk factors were/are most relevant?

19. Epidemiological studies • Descriptive studies Person Place Time Person

20. Epidemiological studies • Descriptive studies Person Place Time

21. Epidemiological studies 1 2 • Descriptive studies Person Place Time • Rapid rise of sick people • Gradual rise

22. Experimental studies Experimental studies are done mostly to assess the value of a particular intervention or treatment, such as antimicrobial drug therapy. • Placebo • Double-blind

24. Endemic Epidemic Pandemic Morbidity Mortality Rates of Disease in a Population

25. Endemic - disease constantly present in a particular geographic area Epidemic - disease with an unusually high occurrence Pandemic - worldwide severe epidemic Morbidity - illness (morbidity rate) Mortality - death (mortality rate) Rates of Disease in a Population

26. Infectious Disease Surveillance CDC - National Centers for Disease Control and Prevention • MMWR - Morbidity and Mortality Weekly Report • WHO - World Health Organization • Weekly Epidemiological Record

30. Trends in Disease • Reduction & Eradication of Disease • Emerging Diseases

31. Trends in Disease • Reduction & Eradication of Disease - Improved sanitation - Reservior & vector control - Vaccination - Antibiotic treatment (Smallpox, eradicated globally)

32. Trends in Disease • Emerging Disease - Microbial Evolution, drug-resistance strain - Population expansion - Mass distribution & importation of food - Climate change

33. Nosocomial Infections(hospital-acquired infections)5-6% patients, $4.5 billion cost Enterococcus species. Part of the normal intestinalflora urinary, wound & blood infections Escherichia coli. Part of the normal intestinal flora Most common cause nosocomial urinary infection Pseudomonas species. Grow in moist environment Staphylococcus species. Normal skin flora Common cause of nosocomial pneumonia and surgical site infection

34. Epidemiology • Principles of Epidemiology • Epidemiological studies • Infectious Disease Surveillance • Trends in Disease • Nosocomial Infections