Disease and Epidemiology 2022-2023 PDF

Disease and Epidemiology Communicable diseases and Non-communicable disease Non communicable diseases (NCDs), also known as chronic diseases, tend to be of long duration...

Disease and Epidemiology Communicable diseases and Non-communicable disease Non communicable diseases (NCDs), also known as chronic diseases, tend to be of long duration and are the result of a combination of genetic, physiological, environmental and behaviours factors. A communicable disease is an illness due to a specific infectious (biological) agent or its toxic products capable of being directly or indirectly transmitted from man to man, from animal to man, from animal to animal, or from the environment (through air, water, food, etc..) to man. Importance of Studying Communicable Diseases Epidemiology  Changes of the pattern of infectious diseases  Discovery of new infections  The possibility that some chronic diseases have an infective origin. Epidemiologist? à Carry out disease surveillance—the observation, recognition, and reporting of diseases as they occur à analyze the data provided by local and national health authorities to reveal trends and signals of disease outbreaks. Each dot represents  The Scope of Disease a disease case or outbreak. (a)  Endemic diseases have a relatively stable pattern of occurrence in a Endemic diseases are present given geographical area or population group at relatively high prevalence in the population in specific geographical areas. (b) and incidence. Epidemic diseases show high  Endemic diseases such as malaria are among the major health problems incidence in a wider area, in low-income tropical countries. If conditions change in the host, the usually developing from an agent or the environment, an endemic disease may become epidemic. endemic focus. (c) Pandemic diseases are distributed  Epidemic when it simultaneously infects an unusually high number of worldwide. individuals in a population; endemic disease is one that is constantly present—typically in low numbers—in a population.  Epidemics are defined as the occurrence of cases in excess of what is normally  expected in a community or region. When describing an epidemic, the time period,geographical region and particulars of the population in which the cases occur must be specified.  implies that the pathogen may not be highly virulent or that the majority of individuals in the population may be immune, resulting in low but persistent numbers of cases.  are reservoirs of infection, a source of infectious agents from which susceptible individuals may be infected.  Characteristics of Disease OUTBREAK? Endemic à Endemic refers to the constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area à The amount of a particular disease that is usually present in a community is referred to as the baseline or endemic level of the disease. à Occasionally, the amount of disease in a community rises above the expected level. Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area. Characteristics of Disease Epidemics  Types of epidemics. The shape of the curve that plots incidence of an epidemic disease against time identifies the likely type of the epidemic.  Common- source epidemic, such as cholera resulting from contaminated water shared by many people, the curve rises sharply to a peak and then declines rapidly.  Host-to-host infectious disease incidence rises relatively slowly as new cases accumulate-propagated- A propagated outbreak in epidemic results from transmission from one person to another. Usually, transmission is by direct person-to-person contact Public health and Infectious Disease  Controls Directed against Common Vehicles and Major Reservoirs  Common vehicles for pathogen dispersal include food, water, and air.  Immunization  Smallpox, diphtheria, tetanus, pertussis (whooping cough), mea- sles, mumps, rubella, and poliomyelitis have been controlled pri- marily by immunization. Diphtheria, for example, is no longer considered even endemic The introduction of a measles vaccine eliminated measles as a common childhood infection within 20 years.  SARS-COV-2 Endemic? Public health and Infectious Disease à Isolation, Quarantine, and Surveillance à Isolation and quarantine are effective public health measures. Isolation is the separation of persons who have an infectious disease from those who are healthy. à Quarantine is the separa- tion and restriction of well persons who may have been exposed to an infectious disease to see if they develop the disease. à Pathogen eradication à Concerted disease eradication programs can sometimes completely eradicate an infectious disease and such was the case with naturally occurring smallpox, eradicated worldwide in 1980.  The Scope of Disease  a pandemic is a widespread, usually global epidemic. An endemic disease Individuals infected with a pathogen that causes an endemic disease  Sporadic cases of a disease occur one at a time in geographically separated areas, suggesting that the cases are not related.  A disease outbreak is the appearance of a large number of cases in a short time in an area previously experiencing only sporadic or endemic diseases  Emerging and re-emerging infections  In the last decades of the 20th century, more than 30 previously unknown or formerly well controlled communicable diseases emerged or re-emerged HIV/AIDS has had the greatest impact.  The viral haemorrhagic fevers include: Ebola,Marburg, Crimean-Congo, yellow fever, West Nile and dengue. Other problematic viruses include poliomyelitis, the SARS coronavirus and influenza A  The Scope of Disease  Subclinically infected individuals are frequently carriers of the particular pathogen, with the pathogen reproducing within them and being shed into the environment where it can infect others.  Virulence a measure of the relative ability of a pathogen to cause disease.  Some pathogens are highly virulent while others are only weakly so Disease Incidence and Prevalence à The incidence of a particu- lar disease is the number of new cases in a population in a given time period à The prevalence of a given disease is the total number of new and existing disease cases in a population in a given time period à Disease incidence is a rate function and is defined as the number of new cases over a given time period (day[s], week, month, etc.); incidence is an indicator of infection risk. Disease prevalence is the total number of diseased individuals at some time point and is a snapshot of the extent of a disease in a population at any given time. Differences? à Mortality, Morbidity, and DALY à The terms morbidity and mortality are commonly used in epide- miology. Mortality is the incidence of death in a population. à Morbidity is the incidence of disease in a population and includes both fatal and nonfatal diseases. à disability-adjusted life year (DALY) the reduction in life quality and productivity due to a disease. is a quantitative measure of disease burden and is defined as the cumulative number of years lost due to an illness itself, a disability due to an illness (whether an infectious disease or not), or premature death. Infectious Disease Model Infectious Disease Model PHASES DURING INFECTION àprodome period/prodromal phase short period during nonspecific/mild symptoms, indicating onset of disease Invasive phase individu experience the typical signs of disease, acme greatest intensity of symptoms where pathogen invade and damage tissues also known as fulminating àDecline Phase period of illness which host defences and treatment overcome pathogen PHASES DURING INFECTION à Covalescense period healing phase ,tissues are repaired, body regain strength and recovers latent period is the time from infection to onset of the ability to infect; à prodromic period is the time between the perception of illness by the host and the appearance of signs and symptoms based on which a clinical diagnosis of the disease is possible; à communicable period (or duration of infectiousness) is the time interval during which the infected host, ill or not, eliminates an agent to the environment and new susceptible individuals can become infected. Herd Immunity à If a high enough proportion of the individuals in a population are immune to a pathogen, then the whole population can be protected, resulting in a collective level of resistance to infection called herd immunity Herd Immunity à If a high enough proportion of the individuals in a population are immune to a pathogen, then the whole population can be protected, resulting in a collective level of resistance to infection called herd immunity  R0 is an estimate of the speed at which a particular infectious disease can currently spread through a Herd Immunity given population. Specifically, it refers to the number of people that one person can transmit on average. Typically, the R0 varies between