Lecture-09 Epidemiology and Disease Transmission PDF

Lecture-09 Epidemiology and disease transmission What is epidemiology? Various terms used in epidemiology and infectious diseases Transmission of disease Types of epidemiology Dr. Manish Kumar Stages of clinical infections No si...

Lecture-09 Epidemiology and disease transmission What is epidemiology? Various terms used in epidemiology and infectious diseases Transmission of disease Types of epidemiology Dr. Manish Kumar Stages of clinical infections No sign or No sign or symptoms symptoms illness  Terms used in infectious diseases Severity Common cold and TB, duration of the disease TB, Herpes Extent at which host body is HIV affected Sequence TB, of the Streptococcus infection Nosocomial infections also called hospital acquired infections cost millions of dollars every year Can be reduced by precautionary measures -like washing hands -periodic training to health care employee -Judicious use of antibiotics and rotation Nosocomial infection in the United States, 2011 Major Site of Infection Estimated total Pneumonia No. 721,800 Gastrointestinal Illness Urinary Tract Infections Primary Bloodstream Infections Cost : $35-45 Surgical site infections Billion Other types of infections  Types of nosocomial infections Exogenous infections Endogenous infections : normal microbiota turning in to opportunistic pathogen Iatrogenic : doctor induced infections (during surgical procedure) or antibiotic therapy resulting in C. difficile associated diarrhea. A fomite is any object or substance that can carry infectious organisms. Clothing, hair. Out break A disease outbreak occurs when a number of cases are observed, usually in a relatively shortperiod of time, in an area previously experiencing only sporadic cases of the disease. Subclinical infections Diseased individuals who show no symptoms or only mild symptoms have subclinical infections. Subclinically infected individuals are frequently identified as carriers of a particular disease.  Epidemiology Epidemiology is the study of the distribution and determinants of disease in populations. Public health – Prolonging life – Prevent disease – Promote health Watch the following you tube links. These video will give you some idea what epidemiologists do and how epidemiology works for public health? https://www.youtube.com/watch?v=Ez4gyB3XDTc http://www.youtube.com/watch?v=KNwM2pKdbZg  Epidemiology of infectious diseases Frequency of Disease – Epidemiologists track occurrence of diseases using two measures Incidence – Number of new cases of a disease in a given area during a given period of time Prevalence – Number of total cases of a disease in a given area during a given period of time – Occurrence also evaluated in terms of frequency and geographic distribution  This curve represent the incidences and the estimated prevalence of AIDS among US adults. Note that scale of two curves are different. Why can the incidence of a disease never exceed the prevalence of that disease ? Occurrence of disease  Epidemiology Terms Incidence Index case (first Prevalence patient known to have Sporadic disease) Reservoir Endemic Period of Epidemic communicability Pandemic Morbidity and Zoonose mortality  Epidemiology Science of how disease spreads John Snow (1813-1858) identified water pump in London as potential source of cholera in 1854. It is regarded as the founding event of the science of epidemiology.  Epidemiology History Gaetan Dugas Mary Mallon (typhoid Mary) HIV spread (patient zero ?) https://www.wnyc.org/radio/#/ondemand/169885  Transmission of Disease Communicable disease (contagious disease) – Spread from sick person or carrier Non-communicable disease (non-contagious) Human to human – Vertical – Horizontal Vector (animal, arthropod, fomite, contaminated food/water, etc) Transmissio n of disease  Epidemiological Methods Descriptive Epidemiology Describes the distribution of disease based on Race, age, sex, place, time Analytical Epidemiology – To determine the cause , mode of transmission and possible means of prevention – Cohort study (test effectiveness of new medical treatment, vaccine, etc) – Clinical trials sometimes involve epidemiology testing (randomized double-blind) Experimental epidemiology Testing a hypothesis i.e. involvement of Chlamydophila pneumoniae in arteriosclerosis resulting in heart attack.  Center for disease control (CDC) http://www.cdc.gov Emerging Infectious Diseases, Morbidity and Mortality Weekly Reports (MMWR) (published by CDC) A detailed list is available on CDC website How public agencies work to limit the spread of disease? Data sharing among health organizations Interrupting/ controlling disease transmission by – Cleanliness of food and water supply – Controlling vectors – Quarantine measures – Enforce immunization Public health education  Examples of Public Health Investigations Multistate Outbreak of Listeriosis Linked to Soft Cheeses Distributed by Karoun Dairies, Inc. – http://www.cdc.gov/listeria/outbreaks/soft- cheeses-09-15/index.html Salmonella outbreak in peanut butter (Trader Joe’s Valencia Creamy Peanut Butter Recall) – Sept 24, 2012 (CDC website) – http://www.cdc.gov/salmonella/bredeney-09-12/  Representative Timeline for Reporting of Case (Salmonella example from CDC) Patient eats contaminated food Becomes ill after 1-3 days Contact doctor within 1-6 days of becoming ill (provide stool sample) – 1-3 days for diagnosis Culture shipped to public health lab – 1-3 days Serotyping and DNA fingerprinting (strain ID) can take 2-10 days Case confirmed as outbreak (can take total of 3-4 weeks)  Emerging and reemerging diseases Emerging : – have not occurred in humans before – have occurred previously but affected only small numbers of people in isolated places (AIDS and Ebola hemorrhagic fever are examples); or – have occurred throughout human history but have only recently been recognized as distinct diseases due to an infectious agent (Lyme disease and gastric ulcers are examples). Watch the following video https://www.youtube.com/watch?v=QLG_-oaYy2s  Reemerging diseases Re-emerging infectious disease: Infectious agents that have been known for some time, had fallen to such low levels that they were no longer considered public health problems & are now showing upward trends in incidence or prevalence worldwide. Examples : rabies, pertussis, malaria, tuberculosis