Infection Control and Isolation

The Chain of Infection

The chain of infection is defined as a sequence of necessary pieces that must be present for an infection to occur. This chain consists of six distinct links: the infectious agent, the reservoir, the portal of exit, the mode of transmission, the portal of entry, and the susceptible host. Each link must be intact for the infection to spread; breaking any link in the chain effectively prevents the transmission of infection.

Infectious Agents and Reservoirs

An infectious agent is any substance or organism that is capable of causing disease, which includes bacteria, fungi, viruses, parasites, or prions. The reservoir acts as the habitat for this infectious agent; it is the specific place where the agent lives, grows, and reproduces or replicates itself. The environment provided by the reservoir allows the pathogen to survive and potentially spread to a new host.

Portals of Exit and Entry

A portal of exit refers to the specific means by which an infectious agent leaves the reservoir to find a new host. Conversely, a portal of entry is the site through which the infectious agent enters a new host's body. This can be any body orifice, such as the ears, nose, or mouth, or it can occur through the skin. The portal of entry provides the necessary location for the infectious agent to begin replicating or for a toxin to exert its effects.

Susceptible Host

A susceptible host is required for an infectious agent to take hold and ultimately become a reservoir for further infection. It is important to note that exposure to an infectious agent does not guarantee that a person will become ill; susceptibility depends on various factors of the host's immune system and health status.

Contact Precautions and Transmission

Contact precautions are implemented when microorganisms are transmitted from an infected person to another individual. Clients requiring these precautions must be placed in a private room. The required Personal Protective Equipment (PPE) for healthcare workers includes gloves and a gown. In addition to PPE, other non-PPE items such as disposable equipment (for example, a disposable stethoscope) are used to prevent cross-contamination between patients. Diseases that necessitate contact precautions include Staphylococcus aureus, Extended-spectrum beta-lactamases (ESBLs), and MRSA. Clostridium difficile specifically requires enteric precautions, a subset of contact precautions.

Transmission by contact is categorized into two types. Direct contact transmission occurs when microorganisms move directly from an infected person to another without any intermediary object or person; examples include herpes simplex virus (HSV), scabies, or blood contacting an open abrasion. Indirect contact transmission involves the movement of microorganisms via a contaminated object or person. Staphylococcus aureus is particularly well-known for its ability to spread through indirect contact.

Droplet Precautions

Droplet precautions are used when respiratory droplets from a client's respiratory tract travel through the air and come into contact with the mucosa of a host. Clients under these precautions must be in a private room and are required to wear a mask whenever they leave their room. PPE requirements for staff include gloves and a mask or a mask with a face shield. Common diseases requiring droplet precautions include Norovirus, Rhinovirus, Coronavirus, Influenza, and Pertussis.

Airborne Precautions

Airborne precautions are indicated when small infectious particulates move through the airspace of another person. Because these particulates remain suspended in the air, clients must be placed in a private room equipped with negative-pressure airflow. The specific PPE required for anyone entering the room is an N-$95$ mask. Diseases that spread via the airborne route include Varicella, Rubeola, Tuberculosis (TB), and Covid-$19$.

Immunity and the Inflammatory Response

Nonspecific immunity involves the action of neutrophils and macrophages, which function as phagocytes. These cells work to eat and destroy microorganisms to protect the body from harm. Both of these cell types are released during the body's inflammatory response. Specific immunity, by contrast, involves antibodies (also called immunoglobulins) and lymphocytes. Antibodies bind to infectious agents and signal white blood cells and the complement system to destroy the invaders.

The inflammatory response is a structured four-step process. In Step $1$, pattern receptors on the surface of cells recognize harmful stimuli. In Step $2$, inflammatory pathways are activated. In Step $3$, inflammatory markers are released into the system. Finally, in Step $4$, inflammatory cells are recruited to the site of the stimulus to begin the healing and defense process.

Stages of Infection

Infection typically progresses through five distinct stages. The first stage is Incubation, where the pathogen enters the host and begins to multiply. The second stage is Prodromal, characterized by the onset of initial, often vague, symptoms. The third stage is Acute illness, where the specific manifestations of the infectious disease are obvious and may reach their peak severity. The fourth stage is Decline, where those manifestations begin to wane as the infectious load decreases. The final stage is Convalescence, during which the client returns to their normal state of health or establishes a "new normal."

Local vs. Systemic Infections and Sharps Safety

Infections are classified as either local or systemic. Local infections are confined to a single area of the body and are typically treated with topical or oral antibiotics. Systemic infections often begin as local infections but eventually enter the bloodstream, allowing them to affect the entire body. For safety, nurses must engage the safety device on a needle immediately after use. Sharps containers should be replaced once they are $3/4$ (three-fourths) full to prevent accidental needle sticks.

Hand Hygiene and Medical Asepsis

Hand hygiene is a broad term for any form of hand cleansing. This includes using soap and water—where nurses should wash for $15-30$ seconds—alcohol-based hand sanitizers, antiseptic handwashes, or surgical hand antisepsis. Alcohol-based sanitizers are considered an acceptable method of hygiene. When rinsing soap off, hands should be held below the level of the elbows. Despite hand hygiene being the single most important step in preventing infection spread, compliance among staff remains below $50\%$. Clients should also be educated on the importance of hand hygiene.

Medical asepsis, or "clean technique," refers to the elimination and absence of disease-causing microorganisms. Best practices include placing blood-soiled blood pressure cuffs in waterproof containers rather than using disinfectant directly on the cuff, removing all visible material from equipment prior to disinfection, and using high-level disinfectants for specialized tools like endoscopic equipment. Protective eyewear is mandatory when cleaning equipment that is soiled with organic material.

Healthcare-Associated Infections (HAIs) and Standard Precautions

Standard precautions represent the infection prevention practices applied to every client, regardless of their known infection status. Healthcare-Associated Infections (HAIs) are a significant concern, with $1$ out of every $31$ clients obtaining an HAI during their stay at a facility. There are four major types of HAIs: Central Line-associated Bloodstream Infections (CLABSIs), which involve PICC lines (peripherally inserted central catheters) or midline catheters; Catheter-associated Urinary Tract Infections (CAUTIs), which involve indwelling urinary catheters; Surgical Site Infections (SSIs), occurring at any surgical location; and Ventilator-assisted Pneumonias (VAPs), which involve mechanical ventilation. It is the nurse's professional responsibility to know what PPE is required for different scenarios and to don and doff that equipment correctly.