3 Disease Transmission To cause disease, a pathogenic organism must: Leave original hostSurvive in transitBe delivered to a susceptible hostIt is important to consider the chain of events leading to disease transmission when developing infection control strategies. To cause an infection, a pathogen must leave the original host, survive outside of the host in transit, be delivered to a susceptible part of the host (such as eyes, nose, mouth), and escape host defenses. In order to cause disease, the pathogen needs to multiply in the host and cause tissue damage. Good infection control practices can interrupt this process.Reach a susceptible part of the hostEscape host defensesDiseaseMultiply and cause tissue damage
4 Routes of Transmission Contact: Infections spread by direct or indirect contact with patients or the patient-care environment (e.g., shigellosis, MRSA, C. difficile)Droplet: Infections spread by large droplets generated by coughs, sneezes, etc. (e.g., Neisseria meningitidis, pertussis, influenza)Airborne (droplet nuclei): Infections spread by particles that remain infectious while suspended in the air (TB, measles, varicella, variola)If a person is to acquire an infectious agent, some type of contact between the susceptible host and the pathogen must occur.Some agents are spread through direct contact, while others are spread through indirect contact. Direct transmission occurs when microorganisms are transferred from one infected person to another person. For example, transmission through direct contact can occur if blood or body fluids from a patient directly enters a caregiver’s body through contact with a mucous membrane or breaks (i.e., cuts, abrasions) in the skin.Indirect transmission involves the transfer of an infectious agent through a contaminated intermediate person, object or surface. For example, healthcare workers can transmit infections with contaminated hands. Objects such as thermometers or shared toys can transmit infections if they are shared between patients without proper cleaning and disinfection. Agents such as Shigella, MRSA, and C. difficile are spread by contact transmission.Respiratory droplets carrying infectious pathogens transmit infection when they travel directly from the respiratory tract of the infectious person to susceptible mucosal surfaces of the recipient, generally over short distances (i.e approximately 3-6 ft or 1-2 m). For example, respiratory droplets are generated when an infected person coughs, sneezes, or talks, or during procedures such as suctioning or endotracheal intubation. Organisms transmitted by the droplet route do not remain infective over long distances, and therefore do not require special air handling and ventilation. Some infectious agents transmitted by the droplet route also may be transmitted by the direct and indirect contact routes. Examples of microorganisms transmitted by the droplet route are Neisseria meningitidis, Bordetella pertussis, and influenza virus.Airborne transmission occurs by dissemination of small particles (or droplet nuclei) containing organisms that remain infective over long distances. Such particles may be dispersed in air currents and inhaled by susceptible individuals who have not had face-to-face contact with (or been in the same room with) the infectious individual. Preventing the spread of pathogens that are transmitted by the airborne route requires the use of special air handling and ventilation systems. Infectious agents to which this applies include TB, measles (rubeola virus), chicken pox (varicella zoster virus), and smallpox (variola virus).
5 Precautions to Prevent Transmission of Infectious Agents Standard PrecautionsApply to ALL patientsTransmission-based PrecautionsUsed in addition to Standard PrecautionsContactDropletAirborneThere are two tiers of precautions to prevent transmission of infectious agents, Standard Precautions and Transmission-Based Precautions.Standard Precautions are applied to the care of all patients in all healthcare settings, regardless of the suspected or confirmed presence of aninfectious agent. Standard precautions are the basis for all other precautions and are used to ensure protection of the healthcare worker and the patient. Transmission-Based Precautions are for patients who are known or suspected to be infected or colonized with infectious agents which require additional control measures to effectively prevent transmission. These include contact, droplet, and airborne precautions.Information on all of these precautions discussed in this presentation can be found in the CDC isolation guidelines at:
6 Standard Precautions Hand hygiene Respiratory hygiene and cough etiquettePersonal protective equipment (PPE)Based on risk assessment to avoid contact with blood, body fluids, excretions, secretionsSafe injection practicesEnvironmental controlPatient placementThe primary components of standard precautions include: hand hygiene; use of personal protective equipment including gloves, gown, mask, eye protection, or face shield, depending on the anticipated exposure; respiratory hygiene and cough etiquette; and safe injection practices. Standard precautions also include environmental controls, including routine cleaning and disinfection of environmental surfaces in patient care areas, and cleaning/disinfection and safe handling of equipment or items likely to have been contaminated with infectious body fluids. Patient placement involves prioritizing single rooms to patients who are at increased risk of transmitting or acquiring infectious agents or at increased risk of an adverse outcome from infection.Hand hygiene is the primary means of preventing transmission of infectious pathogens. Hand hygiene can be performed with an alcohol-based hand sanitizer or by washing with soap and water. Wash hands with soap and water if hands are visibly dirty or contaminated. When washing hands with soap and water, wet hands first with water, apply soap to hands, and rub hands together vigorously for at least 15 seconds, covering all surfaces of the hands and fingers. Rinse hands with water and dry thoroughly with a disposable towel. Use towel to turn off the faucet. If clean water is unavailable, boiled or bottled water, or water treated with chlorine tablets should be used.Respiratory hygiene/cough etiquette is a part of standard precautions and is a source containment measure. This should be done at the initial point of encounter (e.g., triage and reception areas in emergency departments and physician offices) and resources including hand hygiene stations, tissues, and waste receptacles should be made available at these points of entry. Instruct symptomatic persons to:cover their mouth and nose when sneezing or coughinguse tissues and dispose in no-touch receptaclesobserve hand hygiene after soiling of hands with respiratory secretionswear a surgical mask if tolerated or maintain spatial separation, >3 feet if possible.
7 PPE for Standard Precautions Gloves – when touching blood, body fluids, secretions, excretions, mucous membranes, non-intact skin, contaminated itemsGowns – during procedures or patient-care activities when anticipating contact with blood, body fluids, secretions, excretionsMask, eye protection (goggles or face shield) – during procedures or patient care activities likely to generate splashes or spraysIn certain circumstances, personal protective equipment may be required for standard precautions. This should be based on a risk assessment of anticipated exposure. Gloves should be worn for touching blood, body fluids, secretions, excretions, mucous membranes, non-intact skin, and contaminated items. A gown should be worn during procedures and patient-care activities when contact of clothing/exposed skin with blood or body fluids, secretions, or excretions is anticipated. A mask and eye protection (goggles) or face shield should be worn during procedures and patient-care activities likely to generate splashes or sprays of blood or body fluids.
9 Contact Precautions Patient placement PPE - Gown and gloves Single room or cohort with patients with same infectionIf neither is possible, ensure patients are separated by at least 3 ft (1 m)*Change PPE and perform hand hygiene between patient contacts regardless of whether one or both are on contact precautionsPPE - Gown and glovesDon upon entry to roomRemove and discard before leaving the roomPerform hand hygiene after removalEnvironmental measures/patient care equipmentClean patient room daily using a hospital disinfectant, with attention to frequently touched surfaces (bed rails, bedside tables, lavatory surfaces, blood pressure cuff, equipment surfaces).Use dedicated equipment if possible (e.g., stethoscopes, bp cuffs)Contact precautions are used for patients with known or suspected infections that represent an increased risk for contact transmission such as Shigella, MRSA, and C.difficile.Contact precautions include patient placement, personal protective equipment, and environmental measures and equipment. Patients should be placed in single rooms if available or cohorted with patients having the same infection. If neither option is possible, then patients should be physically separated by at least 3 feet, with a privacy curtain in between to limit direct contact. It is important to emphasize that regardless of whether one or more patients in the same room are on contact precautions, PPE must be changed and hand hygiene performed between patient contacts.For PPE, gowns and gloves should be donned upon entry into the room and removed/discarded before leaving the patient care area. Hand hygiene must be performed after removal of PPE.For environmental cleaning, rooms should be cleaned daily with a hospital disinfectant with special attention to frequently touched surfaces, including bed rails, bedside tables, lavatory surfaces, blood pressure cuff, and equipment surfaces. Patient-dedicated or disposable equipment should be used whenever possible, or shared items should be cleaned and disinfected between patients.
10 Droplet Precautions Patient placement PPE – surgical mask Single room or cohort with patients with same infectionIf neither is possible, ensure patients are separated by at least 3 ft (1 meter)Surgical mask on patient when outside of patient roomNegative pressure or airborne isolation rooms not requiredPPE – surgical maskDon upon entry into roomEye protection (goggles or face shield) if needed according to standard precautionsDroplet precautions are used for infections spread by large droplets generated by coughs and sneezes, such as Neisseria meningitidis, pertussis and influenza. Similarly to Contact Precautions, patients should be placed in single rooms, or if unavailable, placed in rooms with other patients with the same infection. If single rooms or cohorting is not possible, then patients should be separated by at least 3 ft (1 m) with a privacy curtain placed in between patients to minimize the risk of close contact. Infections spread by the droplet route do not require negative pressure or airborne isolation rooms. A surgical mask should be donned upon entry into the patient’s room. (It is not necessary to wear a respirator.) Eye protection should be worn according to standard precaution criteria.
11 Airborne Isolation Airborne infection isolation room (AIIR)* Monitored negative air pressure in relation to corridor6-12 air exchanges/hourAir exhausted outside away from people or recirculated by HEPA filterSurgical mask on patient when not in AIIR (limit movement)PPE – filtering facepiece respiratorFor all personnel inside negative pressure roomInfections transmitted via airborne droplet nuclei require airborne isolation, i.e. the use of special air handling and ventilation systems (e.g., AIIRs) to contain and then safely remove the infectious agent. This applies to infections including TB, measles (rubeola virus), chickenpox (varicella zoster virus), and smallpox (variola virus). AIIRS require monitored negative pressure in relation to the corridor, 6-12 air exchanges/hr, and air must be exausted away from people or recirculated through a HEPA filter. The patient must wear a surgical mask when not in the AIIR. Limit transport and movement of the patient outside of the AIIR to medically necessary purposes. If an airborne isolation room is not available, natural ventilation alone or combined with mechanical ventilation may be a practical alternative in some settings.In addition to AIIRs, respiratory protection with filtering facepiece respirators (NIOSH certified N95 or higher level respirator) is recommended for healthcare personnel entering the AIIR.* Natural ventilation alone or combined with mechanical ventilation may be a practical alternative in some settings.
12 Summary of Precautions HandHygienePrivateRoomGlovesGownMask/RespiratorEye ProtectionStandardYesPRNDropletYes*MaskContactAirborneAIIRThis table gives a summary of the standard and transmission-based precautions just discussed. “PRN” indicates measures that should be taken as needed depending on anticipated exposure risk (see standard precautions).*When possible; cohort if not possiblePRN = as needed
14 Transmission of Influenza Transmitted person-to-person through close contactDroplet, contact, and airborne (short-range) may occurSeveral studies suggest at least some component of airborne transmissionDroplet likely most important (via coughs and sneezes)Influenza is transmitted primarily through close contact, such as during exposure to large respiratory droplets, direct contact from hands to mouth, and short-range exposure to infectious aerosols. However, the relative contribution and clinical importance of each of these modes is unknown. Some observational and animal studies suggest airborne transmission via small particle aerosols, but there are little data to support airborne transmission over long distances or prolonged durations of time. For seasonal influenza, droplet precautions have been recommended by the Healthcare Infection Control Practices Advisory Committee and employed by US healthcare facilities for many years. The fact that significant outbreaks are relatively uncommon in acute care settings suggests that most influenza transmission occurs via large droplets.
15 Contact Transmission Potential Influenza virus survival on surfaces at room temperature and moderate humidity:Steel and plastic: hoursCloth and tissues: 8-12 hoursTransfer to hands possible after inoculation of:Steel: up to 24 hrsTissue: up to 15 minutesEnveloped virus - inactivated by detergents, alcohol, bleach, household disinfectantsThere are limited data evaluating influenza virus survival on surfaces and inactivation. What is available provides indirect support for the feasibility of contact transmission. Influenza virus can survive on surfaces at room temperature and moderate humidity for up to 48 hours on steel and plastic and up to 12 hours on cloth and tissue. Virus can be transferred from steel (such as bedrails and tables) to hands 24 hours after inoculation, but from tissues to hands for only 15 minutes. Because it is an enveloped virus, influenza is easy to inactivate with detergents, alcohol products, bleach, and household disinfectants.
16 Infection Control for Influenza SeasonalAvian, non-pandemicPandemicFor infection control recommendations for influenza, there are 3 situations to address: seasonal influenza, avian influenza, and pandemic influenza. The CDC currently has specific infection control recommendations for each one.
17 Infection Control Challenges for Pandemic Influenza We don’t know which flu virus will cause a pandemicWe don’t know exactly how that virus will be transmittedOther considerationsWe won’t have protection with a vaccine until well into the pandemicMortality might be highNearly everything will be in short supplyInfection control supplies (masks, respirators)AntiviralsRecommendations are likely to evolveThere are important challenges in developing infection control guidelines for pandemic flu.Some important challenges are thatWe don’t know which influenza virus will cause a pandemicWe don’t know exactly how that virus will be transmittedIn addition, we won’t have adjunctive protection with a vaccine initially. Mortality is likely to be high, and nearly everything will be in short supply, including infection control supplies (e.g. masks, respirators) and antiviral medications. This means that we will need to learn quickly and that infection control recommendations will likely evolve as we learn more about transmission or as it changes during the course of a pandemic.
18 Infection Control for Pandemic Influenza: Healthcare Facility Measures Conduct hospital surveillanceEducate staff, patients, family, visitorsDevelop triage procedures for clinical evaluation and admission policiesSegregated waiting areasEnforce respiratory hygiene/cough etiquettePatient placement and cohortingLimit facility accessEstablish occupational health plan for management of sick healthcare workers, cohorting of staffUse of vaccines and antivirals as indicated by public health officialsThere are comprehensive infection control measures that facilities should take in response to pandemic influenza. These are outlined in greater detail in the HHS Pandemic Influenza Plan, supplement 3 ( These measures include conducting hospital surveillance and communicating with public health officials, educating staff, patients, family members and visitors about how to prevent disease transmission, and developing triage procedures at points of entry (e.g. EDs) which include clinical evaluation and admission policies. Such procedures should include segregated waiting areas, enforcing respiratory hygiene and cough etiquette, and patient placement and cohorting strategies. Facilities should limit access of non-essential visitors to the facility. They should establish occupational health plans for issues such as identifying and managing sick healthcare workers and cohorting of staff if necessary. The use of vaccines (“pre-pandemic” and pandemic when available) and antiviral drugs can be implemented with the guidance of public health officials.
19 CDC Recommendations for Reducing Worker Exposure During Pandemic Influenza Use of particulate respirators (N95 or higher) for direct care of patients with confirmed or suspected pandemic flu is prudentReduce worker exposure and minimize demand for respiratorsEstablish specific wardsAssign dedicated staff (healthcare, housekeeping, etc)Dedicate entrances and passagewaysFor reducing worker exposure during pandemic influenza, the CDC recommends the use of particulate respirators (N95 or higher level respirator) for direct care of patients with confirmed or suspected pandemic flu, at least in the initial stages of a pandemic. In addition, as referenced in the previous slides, other measures should be taken to minimize the number of personnel coming into contact with patients, including establishing specific wards for patients with pandemic flu, assigning dedicated staff, and dedicating entrances and passages for flu patients.Since respirators will likely be in short supply during a pandemic, prioritization of use is also recommended. As stated before, N-95 or higher level respirator (e.g. PAPR) should be used for high-risk procedures, in addition to contact precautions and eye protection. High risk procedures include intubation, suctioning, nebulizer treatment, bronchoscopy, resuscitation and direct care for patients with influenza-associated pneumonia.Until more is known, the interim guidance developed by CDC state that “extra precautions might be especially prudent during the initial stages of a pandemic, when viral transmission and virulence characteristics are uncertain, and medical countermeasures, such as vaccine and antivirals, may not be available.”
20 CDC Recommendation for Negative Pressure Rooms Already in very short supplyLittle data to suggest transmission of influenza over long distancesWould not be recommended for routine patient care in an established pandemicIf possible, should be used when performing high-risk aerosol-generating proceduresFor pandemic flu, negative pressure rooms would not be recommended for routine patient care as they will be in short supply and there are no convincing data to suggest transmission of flu over long distances. If possible, negative pressure rooms should be used when performing high-risk aerosol-generating procedures.
21 Comparison of CDC & WHO: Pandemic Influenza Hand HygieneGlovesGownEye ProtectionMask/RespiratorPatient PlacementCDCYESParticulate RespiratorAIIR (negative pressure)WHOPRN*Surgical Mask (respirator for aerosol-generating procedures)Single room, adequately ventilated; cohort if unavailableThis is a comparison slide of CDC and WHO guidelines for patients with known or suspected pandemic influenza.For pandemic influenza, WHO recommends the following:Standard plus Droplet Precautions should be applied for routine patient care of suspected or confirmed pandemic influenza patients. This includes adequate hand hygiene, wearing a medical mask and eye protection if splashes are anticipated. Gloves and gowns should be worn in accordance with Standard Precautions. Patients should be housed in single-patient rooms that are well-ventilated, or if unavailable, cohorted with patients with the same illness. WHO guidelines do not require routine use of AIIR. If aerosol-generating procedures are performed, PPE should include a particulate respirator instead of a medical mask.CDC Interim Recommendations: Infection Control PrecautionsAs with the recommendations for avian influenza H5N1, All patients who present to a health-care setting with fever and respiratory symptoms should be managed according to recommendations for Respiratory Hygiene and Cough Etiquette. Isolation precautions identical to those recommended for SARS should be implemented for all hospitalized patients diagnosed with or under evaluation for pandemic influenza.However, an airborne isolation room would not be used for routine patient care in an established pandemic.*PRN – as needed based on standard precautions
22 Prevention is Primary.First and foremost, avoid exposure. If you can’t avoid the exposure, limit your time and risk of exposure. Also, very importantly, contain the source. Finally, use PPE appropriately.