Public Health Lecture 2 PDF

Public health PM 908 Lecture 2 Dr. Arwa Ramadan Lecturer of microbiology and immunology Contamination Definition: Invasion of pathogenic microorganisms into the tissue or onto the surface of a host or inanimate articles or solutions. The number...

Public health PM 908 Lecture 2 Dr. Arwa Ramadan Lecturer of microbiology and immunology Contamination Definition: Invasion of pathogenic microorganisms into the tissue or onto the surface of a host or inanimate articles or solutions. The number of microorganisms is insufficient to cause infection. Contamination can be very dangerous and cause major outbreaks of infection. 2 The outcome of the Contamination Heal without serious problem. Pathogenic microorganisms replicate and invade the tissues causes tissue damage and interfere with the healing process. Infection control efforts should be done to reduce contamination of the environment in order to prevent transmission of infection 3 Colonization Definition: The presence of microorganisms (on skin, mucous membranes, in open wounds, or in excretions or secretions) that are not causing adverse clinical signs or symptoms. Origin: From the external environment and is associated with the normal flora found on the skin. Site: Frequently occurs in portal of entry e.g Respiratory tract, Genitourinary tract. Common sites include anterior nares of the nose, axillae, groin or tissues (as open wound). 4 Outcome of Colonization Outcome: Either no reaction or only a slight reaction. Colonization is the first step in the infective process. In colonization, replication of the Microorganism is not usually occur or is not enough to cause infection. It is present in almost multicellular organisms. It may be temporary or long-term. The host may become a carrier and shed the organism to infect others (e.g., Nasal MRSA carriers (identified by nasal swab) and carbapenem- resistant Gram-negative bacteria carriers (identified by anal swab) Infection Invasion of the host by different species of microorganisms, multiplication within tissues or on the body surface, damage and or disease. Endogenous infection: Dormant pathogenic microorganisms may reactivate within the host body (e.g. in the case of open Tuberculosis). Exogenous infection: The pathogenic microorganism acquired from the external environment of the host. Opportunistic infection: Overgrowth and invasion of tissues by pathogenic microorganisms in response to suppression of the immune system such as oral candidiasis in diabetic or AIDs patients. Superinfection: Results from long-term use of a wide spectrum of antibiotics depletion of microbial flora.  Incubation Period of the Infection Incubation period: It extends from the time a pathogenic microorganism invades a host until the first signs of infection or the time from invasion until first transmission to other hosts. Its duration is variable from hours to days depending upon the type of pathogenic microorganism as well as the type of the host and the environment. varies from hours to days depending upon the type of pathogenic microorganism, the type of the host, 7 Pseudo-infection Definition: Mismatch between laboratory results (growth) and clinical symptoms and signs (absent). Occurs when there is colonization of a pathogen without evident clinical signs of infection. Results from contamination of specimens if colonization is superficial or in case of lab error. It must be differentiated from true infection in which patients must be properly treated. 8 Pseudo-infection Types: Pseudo-bacteria: contamination of a specimen with normal flora such as Bacillus or Streptococcus spp. Pseudomeningitis: contamination of CSF with bacteria or fungi without matching clinical symptoms. Pseudopneumonia: from contaminated bronchoscopes, respiratory equipment or solutions. Pseudobacteriuria: contamination of external urinary drainage system. 9 Establishing Infections A SUSCEPTIBLE HOST must encounter a VIRULENT organism 1 The organism must gain ACCESS to the host 2 It must move to a favourable site 3 It must MULTIPLY, despite the host defences 10 Collecting the data Preparing an Initial Line List and Epidemic Curve The line list is, perhaps, the single most important tool in any outbreak investigation, and hence merits considerable early discussion and effort. In general, information that can be helpful on a line list can include details about patient signs or symptoms Line Listing – chart of specific cases: some items are abstracted into a table called a “line listing” Data Included in Line Listing (cont…) Demographic information: Age, sex, occupation, hospital number, date of admission, date of surgery…etc. Clinical data: Signs and symptoms, onset, dates and times, outcomes, lab results, antimicrobials, other medications. Exposure information: Procedures or surgery; medical devices or equipment. Any other potentially relevant data A table consisting of important variables such as identification number, age, sex, signs& symptoms, lab test results. New cases are added to a line listing as they are identified Characterize the outbreak by Time: Epidemic Curve (cont…) Epidemic curve or “epi curve” = a graph of the number of cases by their date of onset. An "epidemic curve" shows the frequency of new cases over time based on the date of onset of disease. Graph in which the cases of a disease that occurred during an epidemic (outbreak) are plotted according to the time of onset of illness in the cases. 1- Point/Common Source Outbreaks (Epidemics) (cont…) Shape: A sudden steep upslope, a peak, and a sudden down-slope Interpretation: people are exposed to the same source over a relatively brief period  1- cont. Point/Common Source Outbreaks (Epidemics) Shape - curve will have a plateau instead of a peak. Interpretation: people are exposed to the same source over an extended period. 2- Propagated (Continuing) Epidemic (cont…) Infections are transmitted from person to person in such a way that cases identified cannot be attributed to agent transmitted from a single source. Occur over a longer period rather than in common source. Explosive due to person to person transmission (chickenpox) if secondary and tertiary cases occur. Intervals between peaks usually approximate average incubation period Propagated epidemic curves usually have a series of successively larger peaks, which are one incubation period apart. The successive waves tend to involve more and more people, until the pool of susceptible people is exhausted or control measures are implemented.. Propagated (Continuing) Epidemic Shape: series of progressively taller peaks. Interpretation - person-to-person spread. Infection prevention and control of communicable diseases 20 What is communicable diseases? Communicable diseases are characterized by the existence of a living infectious agent which is transmissible. Apart from the infectious agent, two other factors affect the epidemiology of the infection, namely the host and the environment. Thus the key to any infectious disease is to think of it in terms of the agent, the mode of transmission, the host and the environment. Some Factors that Render Patients More Susceptible to Infection Include: 1. Extremes of age. 2. Underlying diseases. 3. Treatment with antimicrobials, corticosteroids, immune suppressive agents. 4. Irradiation. 5. Break in the first line of defense by surgery, anesthesia and indwelling catheter. 6. Long hospital stay.  Sources of infective agents : Human sources Patient himself or his endogenous flora. Health care personnel (Hands of the nurses and doctors). Visitors ( ex. visitors infected with influenza virus). Persons with infectious disease. Persons with colonization (Nasal MRSA colonization are great threat for immunocompromised patients such as liver transplantation patients). Persons in incubation period. Chronic carriers. Environmental sources: Equipment (CBG and stethoscope , medication and working surfaces (nursing station, keyboards and telephone). Components of Infection Disease Process Causative agent Reservoir of the infection Portal of exit of the organism from the reservoir Mode of transmission of the organism Portal of entry into host Susceptible host 25  1- Reservoir The place where disease(microorganism, pathogen, or causative agent) can grow or multiply. It can be patient, animal, plant, soil, air, water, or the surroundings. Sources of infection: The place from which an organism causing an infection originates i.e. becomes available for cross-infection. It can endogenous or exogenous infection. Fomites: They are the inanimate object which has been contaminated with an organism, and which could act as a source e.g., Towels, sinks, bed rails, and commode (surroundings of the patient). Examples of the reservoir and the associated organisms: Water: can be a reservoir for Pseudomonas spp., Klebsiella spp. And cholera in some countries. Bowel: E. coli and the coliform bacteria Nose: Staph. Aureus and methicillin-resistant staphylococcus aureus (MRSA). 27 2- Portal of Exit The pathway by which microorganisms leave the reservoir. These microbes may Exit through: The bloodstream (through the entry sites of devices such as intravenous catheters and syringes). Skin openings (for example: superficial and deep wounds, rashes, and the site of surgery). Mucous membranes (example: eyes, nose, mouth). Respiratory system (example: bronchi and lungs). Urinary and reproductive system (example: vagina and urethra). Digestive system (example: mouth and anus). 28 3- Modes of Transmission A. Contact: Direct contact Indirect contact B. Droplet mode of transmission C. Air borne mode of transmission. D. Fomites E. Vectors 29 Thank you