infection and control of aerosol transmissable diseases


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this is a series of lectures on microbiology useful for undergraduate medical and paramedical students

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  • The chain model of communicable diseases is a model to understand the factors involved in the spread of infectious diseases. There are 6 links in the chain. All these steps are necessary to spread a “contagious or communicable disease”.
    To stop the spread of disease, one or more of these links must be broken.
    Source: Epidemiologic Methods for the Study of Infectious Diseases, Oxford University Press 2001
  • The first link in the chain of infection is the infectious agent.
    Often called microbes or “germs”. The main agents are bacteria, viruses, fungi, or parasites
    The second link or reservoir are “hiding places” – the usual places where the microbe can live, grow and multiply.
    Reservoirs can be:
    Human (both acute clinical cases who are infectious and carriers). Example: infectious (measles, influenza) and carriers (Hepatitis B, Salmonella typhi)
    Animal (zoonotic diseases) Examples: tularemia, rabies
    Environmental: soil: tetanus, cocci; water: legionnaire’s
    The third link is portal of exit: routes by which the infectious agents escapes the human or animal reservoirs. Some diseases may have several portals of exit.
    Examples: respiratory tract (nasal/respiratory secretions); GI tract (saliva, vomitus, stool); GU tract (urine, semen, vaginal secretions; Breaks in skin: (skin rash, needle sticks, bites of mosquitos)
  • The fourth link is modes of transmission: We’ll discuss more about these in the next slide.
    The fifth link is portals of entry: Same as exit portal or may differ.
    An finally, susceptible host(s) – susceptible either due to lack of immunity to the infectious agent or immune system compromised
  • Communicable Diseases can be transmitted by two different mechanisms: direct transmission and indirect transmission.
    Direct transmission occurs through:
    Contact with infectious body fluids of human/animal. For human to human transmission this is usually through direct contact (e.g. touching, kissing, biting, sexual intercourse).
    Direct contact is one important route of transmission for HIV and Hepatitis B.
    Humans can contract rabies by direct contact with infectious saliva through the bite of a rabid dog or bat.
    Large droplets produced by sneezing, coughing, or even talking (direct transmission). Transmission is by direct spray over a few feet before the droplets fall to the ground (e.g., Pertussis and meningococcal infection).
    Indirect transmission can occur through:
    Common vehicle that is contaminated (e.g., food, water, fomites or inanimate objects like the doorknob), or biologic products (e.g., blood).
    Vector-borne (e.g., malaria, WNV. Lyme disease)
    Airborne (e.g., inhalation route).
    Airborne transmission refers to spread of infectious aerosols, spores, contaminated dust through the air causing diseases primarily by inhalation. Most of us know that TB is transmitted by the airborne route.
    Hanta virus pulmonary syndrome is another disease transmitted by the airborne route.
    Small rodents can carry hanta virus and excrete the virus in their urine.
    Sweeping in enclosed areas with rodent infestations can stir up contaminated dust particles which, if inhaled, can cause a life-threatening acute respiratory disease syndrome in humans.
    Vertical transmission: This is from mother to child, often in utero or during childbirth (also referred to as perinatal infection). It occurs more rarely via breast milk. Example: HIV, Hepatitis B and Syphilis.
    Some diseases are transmitted by multiple routes:
    Malaria, West Nile virus- mosquito (vector), transfusions (vehicle; rare), transplacental (direct; rare)
  • As we heard earlier today
    Infectious aerosols are generated when an some ill person sneezes, coughs or speaks. For some types of infections (such as chickenpox or measles), a person can be infectious even before the onset of symptoms.
  • Expulsion of infectious material into the air through sneezing, coughing or through aerosol-generating medical procedures such as sputum induction creates large droplets and smaller aerosols. Even speaking and breathing can generate smaller amounts of aerosols routes of transmission of respiratory infections
    Bacterial or viral laden droplets (10-100 ) can land on the mucous membranes of the nose, mouth eyes or nearby persons or inhaled
    Highest exposures within 3-6 feet.
    Once in contact with the mucosal surface, an infection can be established in an innocent bystander who is not immune.
    Airborne smaller aerosols created during cough or after evaporation of larger aerosols can remain suspended in the air for longer periods and can be inhaled deeply in the lungs.
    Respiratory secretions contaminate a surface and if transferred to the hands, may then lead to self-inoculation or infection of others
    For instance, TB is transmitted by the airborne route. Household contacts are the most susceptible, but those sharing the same airspace in close quarters (e.g. in airplanes) are also at increased risk of infection.
  • Measles is highly infectious. Transmission is primarily person to person by large droplets. However, airborne transmission has occurred in a closed area (e.g., doctor’s exam room) up to 2 hours after a person with measles has occupied the area.
    Some infections can be transmitted by multiple routes
    RSV – a common respiratory illness in early childhood that causes infant wheezing or bronchiolitis. The virus can survive on non-porous surfaces for hours and some studies have shown that direct transmission by contact with contaminated surfaces is the most common mode of transmission in health care settings
    Influenza: traditionally droplet; increasing evidence for airborne component. The flu virus can survive on hands for 15 minutes and 2-48 hours on surfaces depending on the surface material, temperature and relative humidity.
    Cal/OSHA ATD Standard, Appendix A for list of Aerosol Transmissible Diseases (ATDs) which require airborne and droplet precautions
  • Will find varying concentration of infectious agent in certain body fluids
  • CDC: 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings
  • Diseases may be spread through inhalation of small infectious particles, including respiratory droplets that become smaller in size due to evaporation.
    Airborne Infection Isolation Rooms are intended to prevent transmission of infectious agents suspended in the air that remain infectious over long distances. Requirements include:
    Increased ventilation rate
    Air exhausted directly to the outside or HEPA filtration on exhaust
    H1N1 AIIR not necessary (near aerosol) not infectious over long distances
    Measles is highly communicable and secondary cases have been documented in health care settings over an hour after a measles case left the doctor’s office
    PH recommends that in general exam rooms should not be used for 2 hours
    Facility must have respiratory protection program (education, fit-testing, user seal checks in place)
    Respirator should be donned prior to entry into room and discarded after exit
    Single room preferred; alternative is cohorting
    Patient should be transported with surgical mask
  • CDC describes a hierarchy of infection prevention and control measures ranked in order from overall effectiveness in controlling disease in a population (protecting most of the people to protecting only the wearer).
    The most effective measure is eliminating potential exposures. Examples: patients with mild influenza-like illness stay home, policy to not allow ill visitors.
    Engineering controls do not require an individual employee implement the control. Examples: installing partitions in triage areas and other public spaces to reduce exposures by shielding personnel and other patients; use of negative pressure rooms for aerosol generating procedures.
    Administrative controls are work practices and policies that prevent exposures. Effectiveness is dependent on consistent implementation. Examples: vaccination; masks for symptomatic patients; and promoting respiratory hygiene and cough etiquette.
    Personal protective equipment (PPE) is a last line of defense for individuals against hazards that cannot otherwise be eliminated or controlled. PPE will not be effective if adherence is incomplete or when exposures to infectious patients or ill co-workers are unrecognized.
  • Again, in health care settings, a patient with suspect ATD should wear a mask when around others
    HCW should wear surgical or procedural mask to protect the patient when performing certain procedures such as insertion of central lines/ lumbar punctures & epidurals
    HCW should wear a mask to protect his/her self against ATDs or as part of PPE for anticipated spray or splash
  • infection and control of aerosol transmissable diseases

    1. 1. Infection Control of Aerosol Transmissible Diseases Dr. Ashish V. Jawarkar
    2. 2. The Chain Model of Communicable Diseases Dr. Ashish V. Jawarkar
    3. 3. The Chain Model of Communicable Diseases  Infectious agent  Reservoirs and/or sources – human – animal – Environment  Portal(s) of exit: – Respiratory tract – GI tract – Genital/urinary tract – Breaks in skin Dr. Ashish V. Jawarkar
    4. 4. The Chain Model of Communicable Diseases  Modes of transmission – Direct contact – Indirect contact  Portals of entry  Susceptible hosts Dr. Ashish V. Jawarkar
    5. 5. Modes of Transmission  Direct Transmission – Direct Contact – Droplet  Indirect Transmission  Vertical transmission (mother to – Vector-borne infant) Dr. Ashish V. Jawarkar
    6. 6. Infectious Aerosols Department of Medical Microbiology, Edinburgh University Dr. Ashish V. Jawarkar
    7. 7. Transmission of Infections by Respiratory Aerosols • Droplets: land directly on mucosal lining of nose, mouth, eyes of nearby persons or can be inhaled.  Highest exposures within 3-6 feet. • Airborne: aerosols become smaller by evaporation; small aerosols (≤ 10 microns) remain suspended for longer periods, if inhaled travel deep into the lungs. • Contact: Aerosols/ secretions contaminate nearby surface. Touch surfaces can infect self or others. Relative contribution of three routes varies with agent. Dr. Ashish V. Jawarkar
    8. 8. Modes of Transmission via Infectious Respiratory Secretions  Droplet: meningococcal meningitis, rubella, pertussis, common cold, SARS, influenza*  Airborne: tuberculosis, measles, varicella, smallpox, SARS, avian influenza Indirect contact: (fomite) RSV, SARS *Influenza traditionally droplet, increasing evidence for airborne component  Dr. Ashish V. Jawarkar
    9. 9. Infection Control in a Health Care Setting Dr. Ashish V. Jawarkar
    10. 10. Infection Control in a Health Care Setting  Basic principles  Standard precautions  Transmission-based precautions  Seasonal influenza in health care settings  Vaccination of HCWs  TB screening of HCWs  Proper donning and doffing  Choose your PPE Dr. Ashish V. Jawarkar
    11. 11. Basic Principles    All body fluids are potentially infectious (except sweat) – blood and blood-tinged fluids including openwounds – stool, urine, vomit, respiratory secretions, saliva, semen, vaginal secretions, breast milk, other body fluids such as pericardial and synovial fluids Minimize exposure to potentially infectious body fluids Infection control measures designed to “break the chain” of transmission Dr. Ashish V. Jawarkar
    12. 12. Standard Precautions in Health Care Settings 1. 2. Appropriate hand hygiene Barrier protective equipment: – – 2. if splash, splatter, or sprays can be reasonably anticipated choose appropriate PPE as needed: gloves, gown, mask, eye protection (face shield, goggles) Proper use and handling of patient care equipment Dr. Ashish V. Jawarkar
    13. 13. Standard Precautions in Health Care Settings 4. 5. 6. 7. 8. 9. Proper environmental cleaning and disinfection Proper Handling of Linen Adherence to Bloodborne Pathogens Standards Proper patient placement Respiratory Hygiene/Cough Etiquette Safe injection practices Dr. Ashish V. Jawarkar
    14. 14. Expanded Isolation Precautions: Transmission-based Standards   When standard precautions are not enough Additional measures based on mode of transmission  Contact Precautions  Droplet Precautions  Airborne Precautions Dr. Ashish V. Jawarkar
    15. 15. Transmission-Based Precautions: Contact Precautions  For known or suspected infections that represent an increased risk of spread by direct or indirect contact with the patient or the patient’s environment Dr. Ashish V. Jawarkar
    16. 16. Transmission-Based Precautions: Contact Precautions   Personal Protective Equipment  Gown & Gloves for all patient interactions  Don PPE on entry, discard before exiting room. (in addition to Standard Precautions) Examples: MRSA, C difficile, Norovirus, other GI pathogens, RSV, antibiotic-resistant pathogens Dr. Ashish V. Jawarkar
    17. 17. Transmission-Based Precautions: Droplet Precautions    Single room preferred, no special ventilation Patient: Mask if transport necessary. Instruct on respiratory hygiene/cough etiquette HCWs wear surgical or procedure mask within 6 feet of patient. Eye protection if splash, spray anticipated (in addition to Standard Precautions) Dr. Ashish V. Jawarkar
    18. 18. Transmission-Based Precautions: Airborne Precautions  Airborne Infection Isolation Room (AIIR) if available  Patient: Mask if transport necessary (as tolerated).  Health care workers (HCWs):   N95 respirator prior to entry into room, discarded after exit. Higher level respirators for aerosol-gen procedure. Careful attention to proper putting on & taking off (don/doff) respirator, including seal check.  Hand hygiene before & after don/doff.  Alert others if need to transfer (in addition to Standard Precautions) Dr. Ashish V. Jawarkar
    19. 19. Seasonal Influenza in Healthcare Settings: Isolation Precautions  For aerosol-generating procedures: N95 respirator + standard precautions (gown, gloves, goggles for spray/splash) Dr. Ashish V. Jawarkar
    20. 20. Dr. Ashish V. Jawarkar
    21. 21. Vaccination of HCWs   Protect patients, protect yourself and other HCWs CDC recommends – Measles, mumps, rubella (MMR): vaccinate unless documentation of immunity or previous vaccination – Varicella (chicken pox): vaccinate unless documentation of immunity or previous vaccination – Tdap – Yearly influenza vaccination – Hepatitis B: vaccinate unless documentation of previous vaccination Dr. Ashish V. Jawarkar
    22. 22. Tuberculosis Screening for Health Care Workers  TB screening at hire and then annually for all licensed healthcare facilities (e.g., acute care hospitals, skilled nursing facilities, primary care clinics) Dr. Ashish V. Jawarkar
    23. 23. Sequence for Donning PPE 1. Gown 2. Mask or Respirator Dr. Ashish V. Jawarkar
    24. 24. Sequence for Donning PPE 3. Goggles/Face Shield 4. Gloves Dr. Ashish V. Jawarkar
    25. 25. Sequence for Removal of PPE 1. Gloves Dr. Ashish V. Jawarkar
    26. 26. Sequence for Removal of PPE 2. Goggles/Face Shield Dr. Ashish V. Jawarkar
    27. 27. Sequence for Removal of PPE 3. Gown Dr. Ashish V. Jawarkar
    28. 28. Sequence for Removal of PPE 4. Mask or Respirator Dr. Ashish V. Jawarkar
    29. 29. What Type of PPE Would You Wear?  Giving a bed bath? – Generally none  Suctioning oral secretions? – Gloves and mask/goggles or a face shield – sometimes gown Dr. Ashish V. Jawarkar
    30. 30. What Type of PPE Would You Wear?  Transporting chair? a patient in a wheel – Generally none required  Responding to an emergency where blood is spurting? – Gloves, fluid-resistant gown, mask/goggles Dr. Ashish V. Jawarkar
    31. 31. What Type of PPE Would You Wear?  Taking vital signs – Generally none  Drawing blood from a vein? – Gloves Dr. Ashish V. Jawarkar
    32. 32. What Type of PPE Would You Wear?  Cleaning an incontinent patient with diarrhea? – Gown, gloves  Taking vitals on a patient with suspect TB? – N95 respirator Dr. Ashish V. Jawarkar
    33. 33. Controlling the Spread of Aerosol Transmissible Diseases in Health Care Settings Breaking the Chain Dr. Ashish V. Jawarkar
    34. 34. Aerosol Transmissible Diseases in Health Care and Public Safety Settings  Droplet  Airborne – Meningococcal meningitis – Pertussis – Mumps – Rubella (German measles) – Strep pharyngitis – Influenza – Tuberculosis – Varicella (chickenpox) – Measles – SARS – Avian influenza – Smallpox – Influenza Dr. Ashish V. Jawarkar
    35. 35. Hierarchy of Infection Prevention and Control Measures Elimination of Potential Exposures Protects most people Engineering Controls Administrative Controls PPE Protects only the wearer Dr. Ashish V. Jawarkar
    36. 36. Hierarchy of Control Technologies • Goal is to reduce exposures to a hazard  Order in which these elements are selected to control exposure is important – – – – Elimination of Potential Exposures Engineering controls Administrative and work practice controls Personal protective V. Jawarkar equipment/apparel Dr. Ashish
    37. 37. Elimination of Potential Exposures • Example: patients with mild influenza like illness stay home Dr. Ashish V. Jawarkar
    38. 38. Engineering Controls  Physically separates the employee from the hazard  Does not require employee compliance to be effective  Examples: – physical barriers at triage – airborne infection isolation room for patients with known or suspect airborne infectious diseases Dr. Ashish V. Jawarkar
    39. 39. Administrative Controls/ Workplace Practices    Policies, procedures, and programs that minimize intensity or duration of exposure – Examples:  signs on door of an airborne isolation room  triage, mask symptomatic patient  provide tissues/ masks/hand sanitizer to public Standard procedures/ behaviors in caring for patients e.g. hand hygiene, HCW vaccination Only as good as enforcement Dr. Ashish V. Jawarkar
    40. 40. Personal Protective Equipment  Lowest level of hierarchy - requires employee compliance for efficacy  Means higher elements of hierarchy fail to adequately protect employee  May involve use of gowns, gloves, eye/splash protection or respirators  Last line of defense Dr. Ashish V. Jawarkar
    41. 41. Face Masks vs. N95 Respirators  Loose fitting, not designed to filter out small aerosols  Place on coughing patient (source control)  HCW should wear mask to – protect patient during certain procedures (e.g., surgery, LP) – protect HCW  droplet precautions  Mask + goggles for anticipated spray/splash  Tight fitting respirator, designed to filter the air  Protects the wearer  HCW should wear when concerned about transmission by airborne route Dr. Ashish V. Jawarkar
    42. 42. Aerosol-Generating Procedures  Sputum induction, bronchoscopy, elective intubation and extubation, autopsies  CPR emergent intubation, open suctioning of airways Dr. Ashish V. Jawarkar
    43. 43. Aerosol Transmissible Diseases Breaking the Chain  Source control – stay home, isolate or separate mask patient  Respiratory hygiene, cough etiquette  Hand hygiene  HCW protection • Vaccinate • Droplet – Mask • Airborne- N95 respirator Dr. Ashish V. Jawarkar
    44. 44. Questions? Dr. Ashish V. Jawarkar
    45. 45. Questions? Dr. Ashish V. Jawarkar