Introduction to infections PART 1 Flashcards
What is an infection?
It is the invasion and multiplication of microorganisms in body tissues, especially that causing local cellular injury due to competitive metabolism, toxins, intracellular replication, or antigen-antibody response.
What is immunity?
Immunity is the ability of an organism to resist a particular infection or toxin by an action of a specific antibody or by white blood cell immune response. There are two types, active and passive.
What is active immunity?
Antibodies in the body that neutralise or destroy pathogens. These are specific and can occur via infection or introduction of a weakened form of the disease e.g., vaccine. B cells produce and secrete antibodies activating the immune system to destroy the pathogens. T cells are responsible for cell mediated immunity which is immunity that does not involve antibodies, it is the activation of phagocytes, lymphocytes, and cytokines in response to an antigen.
Where are B and T cells produced and matured?
B cells are both produced and matured in the bone marrow whereas T cells are produced in bone marrow but matured in the thymus.
What is passive immunity?
Immunity which is provided when a person is given antibodies for a disease rather than them developing the antibodies themselves. Newborns acquire this through the placenta.
What is the general immune response?
B cells encounter an antigen, molecule structure found on pathogen surfaces, the antigen binds to the receptor on the B cells and it is taken into the B cell by endocytosis. The antigen is processed and presented on the B-cell surface. T helper cells will bind to the complex, this binding releases cytokines that induce B cells to divide rapidly. These daughter cells either become plasma cells or memory cells. The memory B cells remain inactive until they encounter the same antigen following reinfection then they divide to form plasma cells. The plasma cells produce a large number of antibodies which are released into the circulatory system. These antibodies will bind to antigens attracting macrophages or killer cells to attack and phagocytose them.
What can cause an infection?
- Bacteria
- Viral
- Fungal
- Parasitic
What is a bacteria?
Most are either spherical called cocci or rod shaped called bacilli or spiralled called spirilla.
They do not have membrane bound organelles and have key features like a pili and flagella.
Aerobic bacteria refers to group of micro organisms that grow in the presence of oxygen. Anaerobic bacteria grow in the absence of oxygen and cannot survive in oxygen rich environments.
Gram staining is used to distinguish and classify bacterial groups into gram-negative or gram-positive differentiating these groups by the chemical and physical properties of the cell wall.
- gram-positive have a thick layer of peptidoglycan in a cell wall that retains the primary stain colour crystal violet
- gram-negative has a smaller cell wall that retains the counterstain safranin red. It has both a cell wall and an outer membrane.
What is a virus?
All viruses contain nucleic acid, either DNA or RNA, and a protein coat which encloses the nucleic acid. Virus has also have an outer envelope structure. Viral particles find cells and can disrupt its functioning by invading and injecting their genome into the host DNA. They need to the host metabolic processes to reproduce.
What is a fungi?
These can be topical or systemic and are caused by opportunistic microbes. Sepsis can occur. It is the bodies extreme response to infection and is life-threatening in emergencies. A typical fungus consists of a mass of branched, tubular filaments enclosed by a rigid cell wall.
Opportunistic scenarios include patients who have an overwhelmed immune system e.g., HIV/AIDS or patients on immunosuppressants.
What is a parasite?
A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host. There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites.
These infections are less common in the UK, the most common is malaria.
What is Antibiotic Stewardship?
Antimicrobial stewardship is the systematic effort to educate and persuade prescribers of antimicrobials to follow evidence-based prescribing, in order to stem antibiotic overuse, and thus antimicrobial resistance. It has three main strategies:
- Improve the knowledge and understanding of antimicrobial resistance
- Conserve the effectiveness of existing treatments
- Stimulate the development of new antibiotics, diagnostics and novel therapies
Outline the START SMART, then FOCUS technique utilised when prescribing antibiotics.
STARTING SMART:
- Start antibiotic treatment within 1 hour of diagnosis (or asap in people with life-threatening infections), in keeping with local antibiotic prescribing guidance
- Obtain microbiological cultures before starting treatment if possible
- Documentation (for example the indication, route, dose)
- Duration and /or review date for the antibiotic is key
FOCUSING:
- Review the clinical diagnosis and continuing need for antibiotics within 48−72 hours
With 5 options to consider:
- Stop antibiotics if there is no evidence of infection
- Switch antibiotic formulation from intravenous to oral asap
- Change antibiotic – ideally to a narrower spectrum- broader prn
- Continue antibiotics and document next review date
- Outpatient parenteral antibiotic therapy - OPAT
Outline the OBJECTIVE signs of an Infections
A sign is an objective, observable phenomenon that can be identified by another person. A sign is objective, and a symptom subjective.
Clinical and Biochemical markers include:
- Changes in blood pressure, heart rate, respiratory rate
- Consolidation on Chest X-Ray (patchers on the lungs)
- Worsening renal function, dehydration
- White blood cell count, neutrophils. (REMEMBER THAT NEUTROPHIL COUNT MAY ALREADY BE LOW IN IMMUNOCOMPROMISED PATIENTS E.G, DURING CHEMOTHERAPY)
- Increased platelets
- CRP (C-reactive protein increase)
- ESR may also be elevated
- CURB-65 score used to evaluate a patient
Outline the SUBJECTIVE symptoms of an Infections
A symptom is a subjective experience that cannot be identified by anyone else. A sign is objective, and a symptom subjective. These are physical signs and can vary based on the patient:
- Subjective observations (physical signs):
- Confusion (older people)
- Drowsiness, irritability, poor appetite (children)
- Fever, aches, pains
- Often localised to site of infection
- Ear infection: ear pain/hearing loss/discharge
- Chest infection: cough, sputum production, SOB
- Genito-urinary infection: lower back/flank pain, dysuria,
- Skin infection: tenderness, swelling, erythema, heat, broken, discharge
- Fever (temperature > 37 ̊C), confusion, rigors
- Temperature > 40 ̊C can be harmful to internal organs, > 43 ̊C can be fatal
