Chain of Infection

The transmissibility of microorganisms between infected or colonized persons and susceptible hosts was perhaps most convincingly demonstrated in the 1847 observations of Ignaz Semmelweis, who introduced handwashing to the obstetric wards of an Austrian maternity hospital and subsequently observed a reduction in the rates of puerperal fever.² In this instance, the initiation of hand hygiene after patient contact (cadavers) interrupted the spread of the infectious agent (group A Streptococcus) via the route of transmission (hands). Over time the epidemiologic roles of the susceptible host, the infected person, and the route of infection were more clearly elucidated and came to be known as the chain of infection. The interaction among these three components is dynamic, and infection may be favored when the host is more susceptible, the infectious agent is more virulent, and the route of transmission is more facilitating.

Children, long recognized as not just “little adults,” are unique hosts because of their continuing physical, neurodevelopmental, and immunologic change and development from infancy through adolescence. Children, especially infants, lack immunity to many pathogens because they have not been exposed through infection or immunization. They are prone to multiple viral infections during any year and naturally share them. Young children are not developmentally capable of understanding or performing good self-hygiene.

The nature of a children’s hospital can also put children at risk of developing an HAI. Open design wards and critical care units rather than single-room design, shared toys, pet visiting, and communal play areas provide many opportunities for transmission of infection.

Once admitted to the ICU, children become more vulnerable to infection because of the interventions needed to provide life-sustaining care as well as the close contact of multiple care providers. An infectious agent that is a harmless or helpful commensal in a normal host can become a life-threatening pathogen in the ICU patient. Because of frequent antibiotic use, the spectrum of infecting microorganisms in the hospital, particularly the ICU, are usually more pathogenic that those acquired in the community setting. Finally, the route of transmission of infection in the ICU is facilitated through frequent patient contact by health care workers, use of mechanical devices and medical therapies that disrupt natural defenses, and inadequate attention to infection prevention and control measures that prevent spread of infection to and between patients (Box 97-1).

Routes of Infectious Disease Transmission

Infectious diseases, whether bacterial, viral, protozoal, fungal, or helminthic, are transmitted via one or more of three routes, usually categorized for infection control purposes as contact (direct or indirect), droplet, or airborne (Table 97-1).³

Table 97–1 Modes of Transmission of Microorganisms in the ICU

Contact transmission includes direct contact and indirect contact. Direct contact transmission occurs when organisms are transferred through physical contact from an infected or colonized person to a susceptible host. Indirect contact transmission occurs when microorganisms are passively transferred to a susceptible host via an intermediate object, such as a contaminated medical device, inanimate objects in the patient’s physical environment, or contaminated hands.

Droplet transmission is the transfer of microorganisms through large droplets (≥5 μm in diameter) generated from the respiratory tract of an infected or colonized person (the source) that are propelled 1 to 2 meters from the source and land on the nasal or oral mucosa of the susceptible host or in the immediate environment. The droplets can be propelled from the respiratory tract in the course of coughing, sneezing, vomiting, or singing or during procedures such as suctioning. These large droplets are propelled a distance of less than 2 meters through the air but do not remain suspended in the air; that is, they do not become aerosolized.

Airborne transmission refers to the spread of microorganisms in particles that are very small (<5 μm) and can therefore remain suspended in the air and widely dispersed by currents to places far from the host. Airborne particles are created through the evaporation of large droplets or may exist in dust particles containing skin squames and other debris.

The Infection Prevention and Control team

Prevention of infection in patients receiving health care is the responsibility of all health care providers. Although Infection Prevention and Control Professionals (ICP) provide an essential expertise,⁴ it is important that the PICU team establish ongoing multidisciplinary processes to reduce infection risk. Among the activities the multidisciplinary team will address are the integration of surveillance data into formal plans for improvement of patient care at regular intervals and designing and implementing quality improvement initiatives. The collaborators in these initiatives can be infection control practitioners, the hospital epidemiologist or medical director of infection control, a clinical pharmacist, members of quality and patient safety departments, and representatives from nursing, ICU physicians, and respiratory therapy. Others may be needed depending on the issue at hand, such as housekeeping or information technology.

Isolation Practices: Standard Precautions and Additional (Transmission-Based) Precautions

Schema to classify infection prevention and control techniques have evolved over time from systems in which a microbiologic laboratory isolate was required (e.g., disease-specific Salmonella diarrhea isolation), to systems focused on preventing transmission of blood-borne diseases to health care workers (Universal Precautions), to the present system in which certain practices are followed continuously with all patients and supplemented based on syndromic presentation and/or specific laboratory diagnoses. In Canada and the United States, the procedures and practices that should be continuously practiced in health care settings are termed Standard Precautions and Routine Practices, respectively, and are briefly outlined in Table 97-1. The concept of Standard Precautions, in which the health care worker has a responsibility to practice certain behaviors (e.g., hand hygiene) or use certain interventions (e.g., wear a mask when face-to-face with a coughing patient) based on a recognition of the need to do so rather than because they were asked to do so, has not yet been universally adopted in health care settings. Training in these skills should be considered an essential component of health care worker competency.

Types of isolation practices (routine, additional) are based on the scientific understanding of how infectious diseases are transmitted from a host or inanimate reservoir to a susceptible host and aim to control or eliminate the reservoir or infectious agent, interrupt transmission, and protect susceptible persons.

If a patient has symptoms that could be caused by an infection (e.g., cough, diarrhea, rash) or diagnosis of a communicable infectious disease, then Additional Precautions may be required in addition to Standard Precautions.³ The three types of Additional Precautions are contact, droplet, and airborne. A full description of the rationale for these precautions and the specific information needed to apply them is beyond the scope of this chapter; readers are referred to comprehensive guidelines available from public health agencies such as the U.S. Centers for Disease Control and Prevention (CDC)³ or from the relevant agency in the jurisdiction in which they practice. A useful guide when deciding which type of precautions to use for an individual patient is the “Red Book” of the Infectious Diseases Committee of the American Academy of Pediatrics⁵; each institution will also have its own infection control manual.

The basic components of Standard Precautions are hand hygiene, use of personal protective equipment (PPE) (e.g., gowns, gloves, masks, face shields) based on the nature of the health care worker-patient interaction and the extent of anticipated body fluid exposure, respiratory/cough etiquette, and safe injection practices. As previously emphasized, Standard Precautions are to be integrated into all patient care activities, regardless of the clinical status of the patient. Additional, or transmission-based, precautions are used when the route(s) of transmission are not completely interrupted by using Standard Precautions alone.³

Respiratory Etiquette/Cough Hygiene are measures to contain respiratory secretions and include covering one’s cough (e.g., coughing into a tissue or the elbow), promptly disposing of tissues, and performing hand hygiene after touching respiratory secretions.

Safe Injection Practices are basic principles of aseptic technique in the preparation and delivery of parenteral medication that limit the risk of infectious disease transmission for both the health care provider and the patient. They include preferential use of single-dose over multidose vials and use of sterile, single-use, disposable needles (needleless access devices) and syringes.

Infection Control Practices for special lumbar puncture procedures are the donning of a face mask and sterile gloves by the health care worker when placing a catheter or injecting material into the spinal space. These recommendations were made after a number of postmyelography meningitis cases occurred without such precautions.

Contact Precautions are intended to prevent transmission of infectious agents, including epidemiologically important microorganisms, that are spread by direct or indirect contact with the patient or the patient’s environment. In addition to Standard Precautions, for example, gloves are required for all entries to a patient’s room rather than just when patient interaction will occur.

Droplet Precautions are intended to prevent transmission of pathogens through close respiratory or mucous membrane contact with respiratory secretions. In addition to Standard Precautions, for example, health care workers and others coming within 3 to 6 feet of a patient on Droplet Precautions would be required to wear facial protection (mask, goggles, and/or face shield), a gown, and gloves. A child on Droplet Precautions would generally be placed in a room alone to avoid contact with other children. (Note: Some guidelines refer to a 3-foot perimeter of an infectious person on Droplet Precautions, and others refer to a 6-foot distance. The worldwide experience with the severe acute respiratory syndrome (SARS) virus, in which droplet transmission may have occurred up to 6 feet from the source, has led some jurisdictions to implement a 6-foot perimeter for droplet precautions.)

Airborne Precautions prevent transmission of infectious agents that remain infectious over long distances when suspended in the air. A patient on Airborne Precautions must be placed in a room alone with special air handling and ventilation capacity. PPE that should be donned by health care workers entering the room of a patient on Airborne Precautions includes a gown, gloves, and a surgical (procedure) mask or respirator depending on the disease encountered.

Patient placement is the determination of which physical setting is safest for the child while minimizing risk of transmission of infectious disease from a potentially or definitely infected patient. Within Additional Precautions recommendations include guidance about the need for a single room (e.g., whether shared rooms are acceptable) or whether a room with special air handling is required.

There are inherent safety risks associated with isolation practices. Isolation practices such as single rooms and PPE may limit the number and type of encounters health care workers have with patients because of the cumbersome nature of entering a room, breaking coverage, the discomfort of certain PPE, and the need to come and go to bring equipment, documentation, and other materials.⁶ Limited encounters may inhibit the critical care team’s ability to access and assess accurately the child and family. Adult studies have demonstrated a negative correlation between patient safety and isolation⁷ as well as increased HAI with lower nurse/patient ratios.⁸ Although no conclusions can be drawn regarding recommended staffing levels for isolated patients in the PICU, this evidence suggests that increased vigilance is warranted for these critically ill children.

Hand Hygiene

Contaminated hands of health care workers have been shown in many studies to transmit health care–associated pathogens.^2,9 The World Health Organization Patient Safety initiative on hand hygiene emphasizes five moments for hand hygiene: before touching a patient, before clean/aseptic procedures, after body fluid exposure/risk, after touching a patient, and after touching patient surroundings.⁹

The advent of waterless hand hygiene agents has been a particularly important development for the critical care setting because of superior antimicrobial killing, time saved compared with water-based handwashing, rapid action, no risk of antimicrobial resistance, and the ease with which waterless agents can be stationed close to the point of patient care. Alcohol-based hand rubs are in general the preferred hand hygiene product for all health care settings.^2,9 When hands have visible dirt or organic matter (e.g., blood) they must be cleaned with water and soap.

Although the benefits of proper hand hygiene far outweigh the risks, skin irritation and health care worker attitudes about hand hygiene products can be an impediment to compliance and satisfaction with hand hygiene agents and must be considered when choosing a particular product in a specific health care setting.^9,10

Personal Protective Equipment

PPE consists of clothing or devices donned by health care workers for their safety or protection while performing potentially hazardous patient care activity. To interrupt infectious disease transmission, eye protection (goggles or face shield), masks, gowns, and gloves may be worn as a part of Standard Precautions and Transmission-Based Precautions.

A surgical (procedure) mask provides adequate facial protection against droplets generated from the respiratory tract. Surgical masks are also used for source control (e.g., on a coughing patient) as a part of respiratory hygiene/cough etiquette. To protect against airborne particles, a particulate filtering face piece respirator is required because it is thought to filter at least 95% of the smaller airborne particles.¹¹ Airborne particles are known to be produced in certain infectious diseases (e.g., tuberculosis, varicella, measles) or may be produced during aerosol-generating procedures in the ICU (e.g., intubation) in patients with respiratory infections (e.g. influenza, SARS). The choice of mask type became a controversial topic during the influenza A H1N1 pandemic that began in 2009, with different jurisdictions recommending procedure masks for health care worker protection during non–aerosol-generating procedures in patients with suspected influenza and others recommending respirators. There is little evidence to suggest that influenza is transmitted through the airborne route; in a recent randomized controlled trial surgical masks were not inferior to respirators in preventing influenza transmission.¹² Readers are referred to local public health and infection control authorities for jurisdiction-specific guidance.

Surveillance

Surveillance for HAIs in a PICU is a process in which information about infections acquired after admission are summarized and given back to the care team in a timely manner so that problems can be identified for action. Surveillance has been defined as “a systematic method of collecting, consolidating, and analyzing data concerning the distribution and determinants of a given disease or event, followed by the dissemination of that information to those who can improve outcomes.”¹³

Although an HAI could occur in any body system to a patient admitted anywhere in the hospital, historical systems of total hospital surveillance are no longer seen as wise use of scarce resources. Surveillance “by objective” was introduced in the 1980s and has led to systems focused on “targets” that cause the most morbidity or mortality, are frequent, or are remediable.¹⁴ In the PICU, the most important are BSIs and ventilator-associated pneumonia.^15,16 Other important surveillance targets in the PICU are urinary tract infection associated with catheterization, surgical site infections such as mediastinitis, and acquisition of epidemiologically important pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant enterococcus (VRE).

The National Health Safety Network (NHSN) of the CDC is a national surveillance system that collects data from a sample of health care facilities that voluntarily submit data on the occurrence of certain HAIs. Because standardized methodology and definitions and risk-adjusted data are used in the NHSN, the surveillance data permit recognition of trends, identification of practices associated with prevention of HAIs, and comparison of rates within and between facilities.¹⁷ Relevant to the PICU setting, NHSN reports central line–associated BSI (CLA-BSI) rates (number of infections per central line days), central line utilization ratio (central line days per patient days), urinary catheter–associated infection (UTI) rate and utilization ratios, and ventilator-associated pneumonia (VAP) rate (VAP days per ventilator days) and utilization. It is important to note that these rates are device specific and therefore incorporate the effect of exposure to an important risk factor. Surveillance results from the NHSN are updated periodically and published in medical journals and on the CDC website.

Standard surveillance definitions have been developed by the CDC (Table 97-2).¹⁸ The CDC definitions incorporate subcategories for children younger than 1 year in recognition of the variable clinical presentation of infection by age. However, CDC definitions may be difficult to apply in children, and alternative approaches have been explored.^19–23 Surveillance definitions fulfill a different purpose than inclusion/exclusion criteria for clinical trial enrollment, or than the diagnosis of illness by a clinician. Surveillance definitions consistently identify indicators of HAI over time and between settings.

Table 97–2 Summary of CDC/NHSN Definitions for HIA (2008)

Bloodstream infection	Laboratory confirmed (infections must be primary)	Regardless of age: • Recognized pathogen from ≥1 blood culture, or • Common skin contaminant in ≥2 blood cultures associated with symptoms (fever, chills, hypotension)
		≤1 Year of age: • Common skin contaminant in ≥2 blood cultures, and • Associated with symptoms (fever >38° or <37° C, apnea, bradycardia)
	Clinical sepsis	Applies only to ≤1 year of age: • Symptoms (fever >38° or <37° C, apnea, bradycardia), and • Negative or no blood culture done, and • Physician initiates sepsis treatment and • No primary infection elsewhere
Systemic infection	Disseminated infection	• Infections, usually of viral origin, without an apparent single site of infection and involving multiple organs and systems (e.g., varicella)
UTI	Symptomatic	• ≥105 Microorganisms/mL urine, not >2 species, and symptoms (at least one of the following: fever >38° C, urgency, frequency, dysuria, suprapublic tenderness)
		• Symptoms (at least two of the following: fever >38° C, urgency, frequency, dysuria, suprapublic tenderness) and at least 1 of 5 urinary laboratory criteria or physician diagnosis or treatment for UTI • Separate criteria are available for children ≤1 year without nonspecific symptoms (not referent to the urinary tract) and 1 of 7 laboratory criteria
	Asymptomatic	• Indwelling urinary catheter within 7 days before urine culture, and • ≥105 Microorganisms/mL urine, not >2 species, and • Asymptomatic, or • No indwelling urinary catheter within 7 days of urine culture, and • ≥105 Microorganisms/mL urine, not >2 species in two urine cultures with same organism(s)
Pneumonia (Alternate criteria are used for the diagnosis of pneumonia in adults.)	Clinically defined (infants and children)	• Serial chest radiographs (one or more for patients without underlying disease and two or more for patient with underlying disease) with new or progressive and persistent infiltrate or consolidation or cavitation, or pneumatocoeles (in ≤1 year old), and • Clinical signs and symptoms (vary according to the patient age: ≤1 year or ≥1 year and ≤12 years)
Lower respiratory tract, not pneumonia	Bronchitis, tracheobronchitis, other lung infection	• No clinical or radiographic evidence of pneumonia, and • Two or more symptoms or signs (fever >38° C, cough, new or increased sputum production, rhonchi, wheezing), and • One or more positive cultures from deep tracheal aspirate or bronchoscopy or positive antigen test on respiratory secretions, or • Child ≤1 year with no clinical or radiographic evidence of pneumonia, and • Two or more symptoms or signs (fever >38° C, cough, new or increased sputum production, rhonchi, wheezing, respiratory distress, apnea or bradycardia), and • One or more of the following: positive culture from deep tracheal aspirate or bronchoscopy or positive antigen test on respiratory secretions, or serologic diagnosis
Ear, eye, nose, throat, mouth	Conjunctivitis	• Pathogen cultured from purulent exudate from conjunctiva or contiguous tissues, or • Patient has redness or swelling of conjunctiva or periorbital area and white blood cells and organisms on gram stain or purulent exudate, positive antigen test on exudate, or conjunctival scraping, positive viral culture, serologic diagnosis, or multinucleated giant cells on microscopic examination of conjunctival exudate
	Sinusitis (Separate criteria exist for oral cavity, ear and mastoid infections, eye infections other than conjunctivitis, and pharyngitis, laryngitis, and epiglottitis.)	At least one of the following: • Organism cultured from purulent material from sinus cavity, or • One or more of the following signs or symptoms with no other recognized cause: fever >38° C, pain or tenderness over the involved sinus, headache, purulent exudate, or nasal obstruction, and/or • Positive transillumination or positive radiographic examination
Central nervous system	Intracranial infection	At least one of the following: • Organisms cultured from brain tissue, or • Abscess or intracranial infection seen during surgical operation, or • Selected central nervous system symptoms without another cause and 1 of 4 laboratory criteria, or • Patient ≤1 year with at least 1of 5 selected symptoms and 1 of 5 laboratory criteria
	Meningitis or ventriculitis	• Organisms cultured from cerebrospinal fluid, or • At least one of the following symptoms: fever, headache, stiff neck, meningeal signs, cranial nerve signs, irritability, and • 1 of 5 laboratory criteria, or • Patient ≤1 year with at least of 1 of 5 selected symptoms and 1 of 5 laboratory criteria
	Spinal abscess without meningitis	• Organisms cultured from abscess in the spinal epidural or subdural space, or • Abscess in spinal epidural or subdural space seen during surgery, autopsy, or in histopathologic examination
SSI	Superficial incisional, primary or secondary	• Occurs within 30 days of operative procedure, and • Involves only skin and subcutaneous tissue of the incision, and • At least one of the following: purulent drainage from incision, organisms isolated from aseptically obtained incisional fluid or tissue, one sign or symptom (pain, tenderness, redness, swelling, heat), and • Surgeon opens incision and incision is not cultured or is culture positive
	Deep incisional, primary or secondary	• Occurs within 30 days of operative procedure or within 1 year if an implant is left in place, and • Involves deep soft tissues of the incision, and • At least one of the following: purulent drainage from the deep incision but not from the organ/space of the surgical site, spontaneous dehiscence of surgical site or symptomatic patient has site opened by surgeon and incision is not cultured or is culture positive, abscess found on direct examination (radiologic, histopathologic, or during operation), or surgeon diagnosis
	Organ space, primary or secondary, indicated specific type (e.g., cardiac)	• Occurs within 30 days of operative procedure or within 1 year if an implant is left in place, and • Infection involves any part of the body, excluding superficial or deep incisional areas, opened or manipulated during the operative procedure, and • Patient has one of the following: purulent drainage via a drain placed into organ/space; organisms cultured from aseptically obtained specimen from organ/space; abscess found on direct examination, during reoperation, or by radiologic or histologic examination or surgeon diagnosis
Bone and joint infection (Separate criteria exist for joint or bursa infection and disc space infection.)	Bone (osteomyelitis)	At least one of the following: • Organisms cultured from bone, diagnosis based on direct examination during surgery or on histopathologic examination, or • Two or more symptoms (fever >38° C, localized swelling, tenderness, heat, or drainage at bone site), and • One laboratory finding (positive blood culture or blood antigen test or radiographic evidence of infection)
Cardiovascular system	Mediastinitis (Separate criteria exist for endocarditis, myocarditis, pericarditis and vascular infection.)	At least one of the following∗: < div class='tao-gold-member'> Only gold members can continue reading. Log In or Register to continue Share this: Click to share on Twitter (Opens in new window) Click to share on Facebook (Opens in new window) Related Related posts: Educating the Intensivist Neonatal Respiratory Disease Disorders and Diseases of the Gastrointestinal Tract and Liver Critical Care After Surgery for Congenital Cardiac Disease Gastrointestinal Structure and Function Research in Pediatric Critical Care Tags: Pediatric Critical Care Expert Consult Premium Jul 7, 2016 | Posted by admin in CRITICAL CARE | Comments Off on Health Care–Associated Infection in the Pediatric Intensive Care Unit: Epidemiology and Control—Keeping Patients Safe Full access? Get Clinical Tree Get Clinical Tree app for offline access Get Clinical Tree app for offline access