Epidemiology: Disease Transmission and Chain of Infection

Epidemiology: Disease Transmission and Chain of Infection Objectives  1. describe the nature of epidemiology;  2. explain how a disease is transmitted; and  3. trace the chain of infection. What do they both have in common? Why is the CoVid-19 pandemic compared to the influenza pandemic in 191...

Epidemiology: Disease Transmission and Chain of Infection Objectives  1. describe the nature of epidemiology;  2. explain how a disease is transmitted; and  3. trace the chain of infection. What do they both have in common? Why is the CoVid-19 pandemic compared to the influenza pandemic in 1918?  novel  no one had the  immunity most affected in the 1918 pandemic were relatively young adults between 20 to 40 years old  corona virus affected adults over the age of 65 with underlying health conditions, and most children have much milder symptoms Epidemiology  Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations. It is a scientific discipline that employs sound methods of scientific inquiry, and is data-driven as it relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. One of the most popular movies which featured the science of epidemiology is “Contagion”. In that movie, how was the disease transmitted? Are there other ways disease is transmitted?  There are two general types of diseases: communicable diseases and non-communicable infectious diseases.  Direct contact occurs through skin-to-skin contact, kissing, and sexual intercourse. Direct contact also refers to contact with soil or vegetation that harbour infectious organisms, and to contact via droplet spread.  Indirect transmission refers to the transfer of an infectious agent from a reservoir to a host by suspended air particles (airborne), inanimate objects (vehicles or fomites), or animate intermediaries (vectors).  Airborne transmission occurs when infectious agents are carried by dust or droplet nuclei suspended in air.  The dust includes material that settles on surfaces and are suspended again through air currents.  Droplet nuclei may remain suspended in the air for long periods of time.  For instance, measles can occur in children who come into a physician's office after a child with that disease leaves because the virus remained suspended in the air.  Vehicles that may indirectly transmit an infectious agent include food, water, biologic products (such as blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels). A vehicle may passively carry a pathogen as in the case of hepatitis A. Alternatively, the vehicle may provide an environment in which the agent grows, multiplies, or produces toxins as in the case of improperly canned foods that support production of botulinum toxin by Clostridium botulinum.  Vectors such as mosquitoes, flies, fleas, and ticks, may carry an infectious agent through mechanical means or they may support growth or changes in the agent. For instance, flies carry Shigella on their appendages and fleas carry Yersinia pestis in their gut. In the case of biologic transmission, the causative agent of malaria or guinea worm disease undergoes maturation in an intermediate host before it is transmitted to humans. In epidemiological studies of communicable diseases, disease transmission is only one of the elements involved in the chain of infection. So what else is in the chain of infection?  The traditional epidemiologic triad model holds that infectious diseases result from the interaction of agent, host, and environment. Transmission occurs when the agent leaves its reservoir or host through a portal of exit. It is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host. This sequence is called the chain of infection. Epidemiology: Models of Causality and Levels of Prevention Objectives 1. distinguish the two models of causation in epidemiology; 2. distinguish various levels of prevention in epidemiology; and 3. assess the contribution of epidemiology to the prevention of disease, the promotion of health and wellness, and the development of health policy.  Smoking causes cancer. Is this true? What makes you say so? Many health professionals do argue that smoking increases one’s chances of getting cancer because of these reasons: (1) Of the more than 7,000 chemicals in tobacco smoke, at least 250 are known to be harmful, including hydrogen cyanide, carbon monoxide, and ammonia, and can thus act as carcinogens; and (2) Smoking harms nearly every bodily organ and organ system in the body and diminishes a person’s overall health, making one susceptible to cancer due to weak immune function. What is causation or causality? Causation or causality is an essential concept in epidemiology. However, there is no specific definition of what it is. In reference to causality, a “cause” (which is an event, condition, characteristic, or combination of these factors, that play an important role in producing a disease) is defined. Two models of causation/causality DETERMISTIC – a single cause leads to a single effect. (A causes B, or, A must always be followed by B). PROBABILISTIC - many possible or probable causes lead to a particular effect. In other words, disease outcomes have multiple contributing determinants that may act together to produce a given instance of that disease. Two models of causation/causality DETERMISTIC (Traditional Model for Infectious Disease) Two models of causation/causality PROBABILISTIC/CAUSAL PIE (diseases that appear to have multiple contributing causes without a single necessary one)