MCB3020 Chapter 37: Epidemiology and Public Health Microbiology PDF

37 Epidemiology and Public Health Microbiology 1 Epidemiology Science that evaluates occurrence, determinants, distribution, and control of health and disease in a defined human population Epidemiologist – one who practices epidemiology John Snow was the first epidemiologist – studied cholera in Lon...

37 Epidemiology and Public Health Microbiology 1 Epidemiology Science that evaluates occurrence, determinants, distribution, and control of health and disease in a defined human population Epidemiologist – one who practices epidemiology John Snow was the first epidemiologist – studied cholera in London 2 3 Centers for Disease Control and Prevention (CDC) Located in Atlanta, GA Functions as national focus for – developing and applying disease prevention and control – environmental health – health promotion and health education activities designed to improve the health of the people Worldwide counterpart is the World Health Organization (WHO) located in Geneva, Switzerland 4 Epidemiology Determine: – causative agent – source and/or reservoir of disease agent – mechanism of transmission – host and environmental factors that facilitate development of disease within a defined population – best control measures 5 Epidemiology Terminology Sporadic disease – occurs occasionally and at irregular intervals Endemic disease – maintains a relatively steady low-level frequency at a moderately regular interval Hyperendemic diseases – gradually increase in occurrence frequency above endemic level but not to epidemic level 6 More Terms Outbreak – sudden, unexpected occurrence of disease – usually focal or in a limited segment of population Epidemic – sudden increase in frequency above expected number – index case – first case in an epidemic Pandemic – increase in disease occurrence within large population over wide region (usually worldwide) 7 Epidemiological Methods Public health surveillance – protecting populations/improving the health of communities via education, promotion of healthy lifestyles, and prevention of disease and injury – methodical approach to identify issues review of death certificates field investigation of epidemics investigation of actual cases 8 Remote Sensing and Geographic Information Systems: Charting Infectious Diseases Can be used to study distribution, dynamics, and environmental correlates of microbial diseases Remote sensing (RS) – gathering of digital images of Earth’s surface from satellites and transforming data into maps Geographic information system (GIS) – data management system that organizes and displays digital map data from RS 9 Measuring Frequency of Infection To determine if an outbreak, epidemic or pandemic is occurring, epidemiologists measure disease frequency at single time points and over time Statistics – mathematics dealing with collection, organization, and interpretation of numerical data Three important statistical measures of disease frequency – morbidity rate – prevalence rate – mortality rate 10 11 Morbidity Rate An incidence rate Number of new cases in a specific time period per unit of population # new cases during a specific time # individuals in population 12 Prevalence Rate Total number of individuals infected at any one time Depends both on incidence rate and duration of illness 13 Mortality Rate Number of deaths from a disease per number of cases of the disease # deaths due to given disease size of total population with disease 14 Patterns of Infectious Disease in a Population Infectious disease – disease resulting from an infection by microbial agents such as viruses, bacteria, fungi, protozoa, and helminths Communicable disease – can be transmitted from one host to another 15 Patterns of Infectious Disease in a Population Two types of epidemics – common source epidemic single common contaminated source (food) – propagated epidemic one infected individual into a susceptible group, infection propagated to others 16 Patterns of Infectious Disease in a Population To recognize and measure an infectious disease in a population various surveillance methods used – gathering information on development and occurrence of a disease – collating and analyzing the data – summarizing the findings – selecting control methods 17 Herd Immunity Resistance of a population to infection and to spread of an infectious organism because of the immunity of a large percentage of the population Level can be altered by introduction of new susceptible individuals into population 18 Herd Immunity Level can be altered by changes in pathogen – antigenic shift – major change in antigenic character of pathogen – antigenic drift – smaller antigenic changes 19 Emerging and Reemerging Infectious Diseases and Pathogens 20 Emerging Infections Infectious disease mortality has increased since 1982 in U.S. – incidence of infectious disease due to emerging microbial populations – some are novel or reemerging infectious diseases Hot spots of emerging infectious diseases – northeast U.S., west Europe, Japan, and southeast Australia 21 22 Systematic Epidemiology Focuses on ecological and social factors that influence development and spread of emerging and reemerging diseases Numerous factors have been identified 23 Reasons for Increases in Emerging and Reemerging Infectious Diseases Include: World population growth Increased international travel Habitat disruption Microbial evolution and development of resistance Inadequate public infrastructures 24 More Reasons Changes in ecology and climate Social unrest, wars, and bioterrorism Changes in food processing and agricultural practices Changes in human behavior, technology, and industry Medical practices that lead to immunosuppression 25 Nosocomial Infections Hospital-acquired infections – from pathogens within a hospital or other clinical care facility, acquired by patients in the facility – ~10% of all hospital patients acquire a nosocomial infection Often caused by bacteria that are members of normal microbiota Many hospital strains are antibiotic-resistant 26 27 28 Sources of Nosocomial Endogenous pathogen – brought into hospital by patient or acquired when patient is colonized after admission Exogenous pathogen – microbiota other than the patient’s Autogenous infection – caused by an agent derived from microbiota of patient despite whether it became part of patient’s microbiota following admission 29 Control, Prevention, and Surveillance Nosocomial infections – prolong hospital stays by 4–13 days – result in over $4.5 billion costs – result in 20,000–60,000 deaths annually Proper training of personnel in basic infection control measures – e.g., handling of surgical wounds and hand washing Monitoring of patient for signs and symptoms of nosocomial infection 30 The Hospital Epidemiologist Accreditation by the Joint Commission on Accreditation of Healthcare Organizations must have designated individual directly responsible for developing and implementing policies to monitor and control infections and communicable diseases Reports to infection control committee or similar group 31 Prevention and Control of Epidemics Three types of control measures – reduce or eliminate source or reservoir of infection – break connection between source and susceptible individual – reduce number of susceptible individuals 32 Reduce or Eliminate Source or Reservoir Quarantine and isolation of cases and carriers Destruction of animal reservoir Treatment of sewage Therapy that reduces or eliminates infectivity of cases 33 Break Connection Between Source and Susceptible Individuals Chlorination of water supplies Pasteurization of milk Supervision and inspection of food and food handlers Destruction of insect vectors with pesticides 34 Reduce Number of Susceptible Individuals Raises herd immunity Passive immunity following exposure Active immunity for protection 35 Vaccines and Immunization Vaccine (see Table 37.3 for examples) – preparation of microbial antigens used to induce protective immunity – may consist of killed, living, weakened (attenuated) microbes or inactivated bacterial toxins (toxoids), purified cell material, recombinant vectors, or DNA 36 Vaccines and Immunization Immunization – result obtained when vaccine stimulates immunity Vaccines attempt to induce antibodies and activated T cells to protect host from future infection Vaccinomics is the application of genomics and bioinformatics to vaccine development 37 Adjuvants Are mixed with antigens in vaccines to enhance the rate and degree of immunization Can be any nontoxic material that prolongs antigen interaction with immune cells and stimulates the immune response to the antigen Several types are available 38 Immunized Hosts Vaccination of children should begin at ~2 months Further vaccination depends on relative risk – living in close communities – reduced immunity – international travelers – health-care workers 39 Global Health Considerations ~500,000 infectious disease deaths in developed countries ~18 million infectious disease deaths in lessdeveloped countries Precautions needed for – global travel – clean water, sanitation – health care infrastructure – vaccination 40 Whole Cell Vaccines Most current vaccines active against bacteria and viruses consist of two microbes that are either inactivated (killed) or attenuated (live but avirulent) Considered gold-standard but may be problematic – may not protect – immunosuppressed at risk of getting disease – attenuated may revert to virulent 41 Acellular or Subunit Vaccines Use of purified molecules from microbes avoids some of the risks of whole-cell vaccines Forms of subunit vaccines – capsular polysaccharides – recombinant surface antigens – inactivated exotoxins (toxoids) 42 Recombinant-Vector Vaccines Pathogen genes that encode major antigens inserted into nonvirulent viruses or bacteria which serve as vectors and express the inserted gene Released gene products (antigens) can elicit cellular and humoral immunity 43 DNA Vaccines DNA directly introduced into host cell via air pressure or gene gun DNA taken into nucleus and pathogen’s DNA fragment is expressed – host immune system responds to foreign proteins produced Many DNA vaccine trials are currently being run 44 The Role of the Public Health System: Epidemiological Guardian Network of health professionals involved in surveillance, diagnosis, and control of epidemics Form county, regional, state, national, and international public health organizations 45 46