Legionella/Legionellosis

Classification

General Characteristics

Legionella

• General characteristics:
  • Structure: thin, pleomorphic Pleomorphic Bacteroides rods/ bacilli Bacilli Shigella
  • Gram stain Gram stain Klebsiella: gram negative Gram negative Bacteria which lose crystal violet stain but are stained pink when treated by gram’s method. Yersinia spp./Yersiniosis (poor Gram staining Gram staining Bacteriology)
  • Other stain(s): usually with silver stain 
  • Oxygen requirement: aerobic
  • Invasion and replication in relation to host cell(s): facultative intracellular Facultative intracellular Yersinia spp./Yersiniosis
  • Enzyme(s): 
    • Catalase Catalase An oxidoreductase that catalyzes the conversion of hydrogen peroxide to water and oxygen. It is present in many animal cells. A deficiency of this enzyme results in acatalasia. Nocardia/Nocardiosis positive
    • Oxidase Oxidase Neisseria positive (Legionella pneumophila (L. pneumophila))
• Culture medium: grown on buffered charcoal Charcoal An amorphous form of carbon prepared from the incomplete combustion of animal or vegetable matter, e.g., wood. The activated form of charcoal is used in the treatment of poisoning. Antidotes of Common Poisonings yeast Yeast A general term for single-celled rounded fungi that reproduce by budding. Brewers’ and bakers’ yeasts are saccharomyces cerevisiae; therapeutic dried yeast is yeast, dried. Mycology extract (BCYE) medium with iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements and cysteine Cysteine A thiol-containing non-essential amino acid that is oxidized to form cystine. Synthesis of Nonessential Amino Acids supplementation
• Legionellosis (the disease caused by Legionella):
  • Legionnaires’ disease: atypical pneumonia Atypical pneumonia Mycoplasma
  • Pontiac fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever: fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever and myalgias Myalgias Painful sensation in the muscles. Tick-borne Encephalitis Virus

Clinically relevant species

• L. pneumophila (causes 80%–90% of human infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease)
• L. micdadei (Pittsburgh pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia agent)
• L. anisa
• L. feeleii
• L. longbeachae

Pathogenesis

Epidemiology

• Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency: 8,000–18,000 cases of Legionnaires’ disease per year in the United States
• More common and more severe in older adults 

Reservoir Reservoir Animate or inanimate sources which normally harbor disease-causing organisms and thus serve as potential sources of disease outbreaks. Reservoirs are distinguished from vectors (disease vectors) and carriers, which are agents of disease transmission rather than continuing sources of potential disease outbreaks. Humans may serve both as disease reservoirs and carriers. Escherichia coli

• Natural habitat:
  • Aquatic systems (e.g., lakes, streams)
  • Soil
• In human-constructed aquatic reservoirs:
  • Hot water tanks
  • Dental equipment
  • Drinking water systems
  • Cooling towers
  • Pools/hot tubs
• In water, Legionella exists within biofilms Biofilms Encrustations formed from microbes (bacteria, algae, fungi, plankton, or protozoa) embedded in an extracellular polymeric substance matrix that is secreted by the microbes. They occur on body surfaces such as teeth (dental deposits); inanimate objects, and bodies of water. Biofilms are prevented from forming by treating surfaces with dentifrices; disinfectants; anti-infective agents; and anti-fouling agents. Proteus or as intracellular parasites in protozoa Protozoa Nitroimidazoles.
• Warm temperatures (25°C–42°C (77℉–107℉)) enhance growth.

Transmission

• Inhalation of aerosolized water droplets Droplets Varicella-Zoster Virus/Chickenpox (primary route)
• Aspiration
• No person-to-person transmission

Virulence factors Virulence factors Those components of an organism that determine its capacity to cause disease but are not required for its viability per se. Two classes have been characterized: toxins, biological and surface adhesion molecules that affect the ability of the microorganism to invade and colonize a host. Haemophilus

• Main feature of Legionella pathogenicity: ability for intracellular multiplication
• Adherence and phagocytosis Phagocytosis The engulfing and degradation of microorganisms; other cells that are dead, dying, or pathogenic; and foreign particles by phagocytic cells (phagocytes). Innate Immunity: Phagocytes and Antigen Presentation of Legionella:
  • Bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology attach to the host cell ( alveolar macrophages Alveolar macrophages Round, granular, mononuclear phagocytes found in the alveoli of the lungs. They ingest small inhaled particles resulting in degradation and presentation of the antigen to immunocompetent cells. Acute Respiratory Distress Syndrome (ARDS) and monocytes Monocytes Large, phagocytic mononuclear leukocytes produced in the vertebrate bone marrow and released into the blood; contain a large, oval or somewhat indented nucleus surrounded by voluminous cytoplasm and numerous organelles. Innate Immunity: Phagocytes and Antigen Presentation) promoted by factors including:
    • Pili Pili Filamentous or elongated proteinaceous structures which extend from the cell surface in gram-negative bacteria that contain certain types of conjugative plasmid. These pili are the organs associated with genetic transfer and have essential roles in conjugation. Normally, only one or a few pili occur on a given donor cell. This preferred use of ‘pili’ refers to the sexual appendage, to be distinguished from bacterial fimbriae, also known as common pili, which are usually concerned with adhesion. Salmonella 
    • Lipopolysaccharide Lipopolysaccharide Lipid-containing polysaccharides which are endotoxins and important group-specific antigens. They are often derived from the cell wall of gram-negative bacteria and induce immunoglobulin secretion. The lipopolysaccharide molecule consists of three parts: lipid a, core polysaccharide, and o-specific chains (o antigens). When derived from Escherichia coli, lipopolysaccharides serve as polyclonal b-cell mitogens commonly used in laboratory immunology. Klebsiella 
    • Outer membrane proteins Outer membrane proteins Neisseria
  • Phagocytosis Phagocytosis The engulfing and degradation of microorganisms; other cells that are dead, dying, or pathogenic; and foreign particles by phagocytic cells (phagocytes). Innate Immunity: Phagocytes and Antigen Presentation facilitated by:
    • Human complement 3 (C3)
    • Macrophage infectivity potentiator (Mip) protein
• Legionella survival and replication by forming Legionella-containing vacuole (LCV) facilitated by:
  • Defective organelle trafficking/intracellular multiplication (Dot/Icm) type IV secretion Secretion Coagulation Studies system (T4SS):
    • Recruits the endoplasmic reticulum Endoplasmic reticulum A system of cisternae in the cytoplasm of many cells. In places the endoplasmic reticulum is continuous with the plasma membrane (cell membrane) or outer membrane of the nuclear envelope. If the outer surfaces of the endoplasmic reticulum membranes are coated with ribosomes, the endoplasmic reticulum is said to be rough-surfaced; otherwise it is said to be smooth-surfaced. The Cell: Organelles to the bacterial vacuole
    • Translocates effector proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis to avoid phagolysosomal fusion
  • Type II secretion Secretion Coagulation Studies system (T2SS):
    • Dampens the cytokine response from infected cells
    • Releases degradative enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes and toxins 

Disease process

1. The bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology multiply within the vacuoles, secreting siderophores Siderophores Low-molecular-weight compounds produced by microorganisms that aid in the transport and sequestration of ferric iron. Klebsiella, allowing the uptake of iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements needed for Legionella growth.
2. Eventually, flagella Flagella A whiplike motility appendage present on the surface cells. Prokaryote flagella are composed of a protein called flagellin. Bacteria can have a single flagellum, a tuft at one pole, or multiple flagella covering the entire surface. In eukaryotes, flagella are threadlike protoplasmic extensions used to propel flagellates and sperm. Flagella have the same basic structure as cilia but are longer in proportion to the cell bearing them and present in much smaller numbers. Helicobacter develop, which triggers Triggers Hereditary Angioedema (C1 Esterase Inhibitor Deficiency) caspase-1, leading to apoptosis Apoptosis A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, I.e., DNA fragmentation. It is genetically-programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth. Ischemic Cell Damage.
3. The cell is destroyed, liberating the bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology and allowing infection of other cells.

Host risk factor

• Age > 50 years
• Immunocompromised immunocompromised A human or animal whose immunologic mechanism is deficient because of an immunodeficiency disorder or other disease or as the result of the administration of immunosuppressive drugs or radiation. Gastroenteritis state: 
  • Diabetes Diabetes Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus
  • Acquired immunodeficiency Immunodeficiency Chédiak-Higashi Syndrome syndrome ( AIDS AIDS Chronic HIV infection and depletion of CD4 cells eventually results in acquired immunodeficiency syndrome (AIDS), which can be diagnosed by the presence of certain opportunistic diseases called AIDS-defining conditions. These conditions include a wide spectrum of bacterial, viral, fungal, and parasitic infections as well as several malignancies and generalized conditions. HIV Infection and AIDS)
  • Hematologic malignancies
  • Solid organ transplant recipients
  • Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship on immunosuppressive treatment
• Chronic lung disease
• End-stage kidney disease
• Smoking Smoking Willful or deliberate act of inhaling and exhaling smoke from burning substances or agents held by hand. Interstitial Lung Diseases (impairs the mucociliary action that clears Legionella)
• Alcohol use

Clinical Presentation

Infection with Legionella is known as legionellosis. 

Pontiac fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever

• Very common
• Self-limiting Self-Limiting Meningitis in Children, mild flu-like syndrome
• Resolves spontaneously (no antibiotics needed) and often goes undiagnosed

Legionnaires’ disease

• Presents as atypical pneumonia Atypical pneumonia Mycoplasma: 
  • Cough, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea 
  • Gastrointestinal symptoms: diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia 
  • Neurologic symptoms: headache Headache The symptom of pain in the cranial region. It may be an isolated benign occurrence or manifestation of a wide variety of headache disorders. Brain Abscess and confusion
• Associated with hyponatremia Hyponatremia Hyponatremia is defined as a decreased serum sodium (sNa+) concentration less than 135 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled via antidiuretic hormone (ADH) release from the hypothalamus and by the thirst mechanism. Hyponatremia
• Illness occurs in certain settings:
  • Travel: cruise ships, resorts, hotels
  • Healthcare facilities: hospitals, nursing homes/long-term care facilities
• Sporadic Sporadic Selective IgA Deficiency infection, but can also be associated with epidemic outbreaks Outbreaks Sudden increase in the incidence of a disease. The concept includes epidemics and pandemics. Influenza Viruses/Influenza

Diagnosis

Clinical examination

• Unilateral lobar pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia: 
  • Crackles, decreased breath sounds, enhanced bronchophony on auscultation
  • Tactile fremitus Tactile Fremitus Pulmonary Examination upon palpation Palpation Application of fingers with light pressure to the surface of the body to determine consistency of parts beneath in physical diagnosis; includes palpation for determining the outlines of organs. Dermatologic Examination
  • Dullness on percussion Percussion Act of striking a part with short, sharp blows as an aid in diagnosing the condition beneath the sound obtained. Pulmonary Examination (represents localized consolidation Consolidation Pulmonary Function Tests)
• Atypical pneumonia Atypical pneumonia Mycoplasma: bilateral crackles or unremarkable findings

Diagnostic tests Diagnostic tests Diagnostic tests are important aspects in making a diagnosis. Some of the most important epidemiological values of diagnostic tests include sensitivity and specificity, false positives and false negatives, positive and negative predictive values, likelihood ratios, and pre-test and post-test probabilities. Epidemiological Values of Diagnostic Tests

• Legionella urinary antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination: rapid method (detects L. pneumophila serogroup 1)
• Polymerase chain reaction Polymerase chain reaction Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR) ( PCR PCR Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR)) (e.g., sputum or bronchoalveolar lavage Bronchoalveolar lavage Washing out of the lungs with saline or mucolytic agents for diagnostic or therapeutic purposes. It is very useful in the diagnosis of diffuse pulmonary infiltrates in immunosuppressed patients. Pulmonary Fibrosis specimen)
• Culture: 
  • BCYE medium with iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements and cysteine Cysteine A thiol-containing non-essential amino acid that is oxidized to form cystine. Synthesis of Nonessential Amino Acids 
  • Legionella spp. grow slowly; visible colonies are usually present after 3 days of incubation Incubation The amount time between exposure to an infectious agent and becoming symptomatic. Rabies Virus.
  • Specimen(s):
    • Lower respiratory secretions
    • Lung tissue
    • Pleural fluid
• Smears of clinical specimen(s):
  • Organism not well demonstrated on a Gram stain Gram stain Klebsiella
  • Silver stain (Warthin-Starry and Dieterle)
  • Direct fluorescent antibody Direct Fluorescent Antibody A form of fluorescent antibody technique utilizing a fluorochrome conjugated to an antibody, which is added directly to a tissue or cell suspension for the detection of a specific antigen. Congenital TORCH Infections (DFA) staining (rapid but less sensitive than a culture) 

Blood tests

• Hyponatremia Hyponatremia Hyponatremia is defined as a decreased serum sodium (sNa+) concentration less than 135 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled via antidiuretic hormone (ADH) release from the hypothalamus and by the thirst mechanism. Hyponatremia (rare in other types of pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia)
• Leukocytosis Leukocytosis A transient increase in the number of leukocytes in a body fluid. West Nile Virus
• ↑ Erythrocyte sedimentation rate Erythrocyte Sedimentation Rate Soft Tissue Abscess ( ESR ESR Soft Tissue Abscess)
• ↑ C-reactive protein (CRP)
• ↑ Procalcitonin Procalcitonin Neutropenic Fever (may not occur in atypical pneumonia Atypical pneumonia Mycoplasma)

Chest imaging

• Chest X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests and chest computed tomography Chest Computed Tomography Hemothorax (CT) scan
• Changes consistent with atypical pneumonia Atypical pneumonia Mycoplasma: diffuse reticular opacity Opacity Imaging of the Lungs and Pleura with absent or minimal consolidation Consolidation Pulmonary Function Tests 
• May include unilateral infiltrates, pleural effusion Pleural Effusion Pleural effusion refers to the accumulation of fluid between the layers of the parietal and visceral pleura. Common causes of this condition include infection, malignancy, autoimmune disorders, or volume overload. Clinical manifestations include chest pain, cough, and dyspnea. Pleural Effusion

Management

• Empiric treatment follows guidelines for community-acquired pneumonia Community-Acquired Pneumonia Pneumonia in Children.
• Directed treatment uses the following antibiotics: 
  • Fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones: levofloxacin Levofloxacin The l-isomer of ofloxacin. Fluoroquinolones preferred
  • Macrolides Macrolides Macrolides and ketolides are antibiotics that inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit and blocking transpeptidation. These antibiotics have a broad spectrum of antimicrobial activity but are best known for their coverage of atypical microorganisms. Macrolides and Ketolides: azithromycin Azithromycin A semi-synthetic macrolide antibiotic structurally related to erythromycin. It has been used in the treatment of Mycobacterium avium intracellulare infections, toxoplasmosis, and cryptosporidiosis. Macrolides and Ketolides preferred; drug of choice for children
• Alternative antibiotic options:
  • Doxycycline
  • Trimethoprim-sulfamethoxazole
  • Combination therapy (some regimens include rifampin Rifampin A semisynthetic antibiotic produced from streptomyces mediterranei. It has a broad antibacterial spectrum, including activity against several forms of Mycobacterium. In susceptible organisms it inhibits dna-dependent RNA polymerase activity by forming a stable complex with the enzyme. It thus suppresses the initiation of RNA synthesis. Rifampin is bactericidal, and acts on both intracellular and extracellular organisms. Epiglottitis)
• Legionella is resistant to beta-lactam Beta-Lactam Penicillins antibiotics.
• Legionnaires’ disease is a notifiable disease.

Differential Diagnosis

• Atypical pneumonia Atypical pneumonia Mycoplasma (other etiology): pulmonary infection that presents typically in elderly or immunocompromised immunocompromised A human or animal whose immunologic mechanism is deficient because of an immunodeficiency disorder or other disease or as the result of the administration of immunosuppressive drugs or radiation. Gastroenteritis patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, non-productive dry cough Dry Cough Strongyloidiasis, and extrapulmonary symptoms. Other causes include: Mycoplasma pneumoniae Mycoplasma pneumoniae Short filamentous organism of the genus mycoplasma, which binds firmly to the cells of the respiratory epithelium. It is one of the etiologic agents of non-viral primary atypical pneumonia in man. Mycoplasma and Chlamydophila pneumoniae.
• Influenza Influenza Influenza viruses are members of the Orthomyxoviridae family and the causative organisms of influenza, a highly contagious febrile respiratory disease. There are 3 primary influenza viruses (A, B, and C) and various subtypes, which are classified based on their virulent surface antigens, hemagglutinin (HA) and neuraminidase (NA). Influenza typically presents with a fever, myalgia, headache, and symptoms of an upper respiratory infection. Influenza Viruses/Influenza: a highly contagious, viral infection caused by ribonucleic acid Ribonucleic acid A polynucleotide consisting essentially of chains with a repeating backbone of phosphate and ribose units to which nitrogenous bases are attached. RNA is unique among biological macromolecules in that it can encode genetic information, serve as an abundant structural component of cells, and also possesses catalytic activity. RNA Types and Structure ( RNA RNA A polynucleotide consisting essentially of chains with a repeating backbone of phosphate and ribose units to which nitrogenous bases are attached. RNA is unique among biological macromolecules in that it can encode genetic information, serve as an abundant structural component of cells, and also possesses catalytic activity. RNA Types and Structure) viruses Viruses Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells. Virology. Influenza Influenza Influenza viruses are members of the Orthomyxoviridae family and the causative organisms of influenza, a highly contagious febrile respiratory disease. There are 3 primary influenza viruses (A, B, and C) and various subtypes, which are classified based on their virulent surface antigens, hemagglutinin (HA) and neuraminidase (NA). Influenza typically presents with a fever, myalgia, headache, and symptoms of an upper respiratory infection. Influenza Viruses/Influenza presents with sudden-onset high fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, headache Headache The symptom of pain in the cranial region. It may be an isolated benign occurrence or manifestation of a wide variety of headache disorders. Brain Abscess, rhinorrhea Rhinorrhea Excess nasal drainage. Respiratory Syncytial Virus, non-productive cough, malaise Malaise Tick-borne Encephalitis Virus, and myalgia Myalgia Painful sensation in the muscles. Ion Channel Myopathy. Rapid influenza Influenza Influenza viruses are members of the Orthomyxoviridae family and the causative organisms of influenza, a highly contagious febrile respiratory disease. There are 3 primary influenza viruses (A, B, and C) and various subtypes, which are classified based on their virulent surface antigens, hemagglutinin (HA) and neuraminidase (NA). Influenza typically presents with a fever, myalgia, headache, and symptoms of an upper respiratory infection. Influenza Viruses/Influenza diagnostic tests Diagnostic tests Diagnostic tests are important aspects in making a diagnosis. Some of the most important epidemiological values of diagnostic tests include sensitivity and specificity, false positives and false negatives, positive and negative predictive values, likelihood ratios, and pre-test and post-test probabilities. Epidemiological Values of Diagnostic Tests (RIDTs) detect viral antigens. 
• Acute respiratory distress syndrome Acute Respiratory Distress Syndrome Acute respiratory distress syndrome is characterized by the sudden onset of hypoxemia and bilateral pulmonary edema without cardiac failure. Sepsis is the most common cause of ARDS. The underlying mechanism and histologic correlate is diffuse alveolar damage (DAD). Acute Respiratory Distress Syndrome (ARDS): a severe inflammatory reaction characterized by non-cardiogenic pulmonary edema Pulmonary edema Pulmonary edema is a condition caused by excess fluid within the lung parenchyma and alveoli as a consequence of a disease process. Based on etiology, pulmonary edema is classified as cardiogenic or noncardiogenic. Patients may present with progressive dyspnea, orthopnea, cough, or respiratory failure. Pulmonary Edema. The condition is due to injury to the alveolar-capillary membrane, causing fluid to flood the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy. Multiple possible causes include trauma, sepsis Sepsis Systemic inflammatory response syndrome with a proven or suspected infectious etiology. When sepsis is associated with organ dysfunction distant from the site of infection, it is called severe sepsis. When sepsis is accompanied by hypotension despite adequate fluid infusion, it is called septic shock. Sepsis and Septic Shock, pneumonitis Pneumonitis Human Herpesvirus 6 and 7, pulmonary infarction, and transfusion-related acute injury.
• Bronchitis: a lower respiratory tract infection that causes inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the bronchi Bronchi The larger air passages of the lungs arising from the terminal bifurcation of the trachea. They include the largest two primary bronchi which branch out into secondary bronchi, and tertiary bronchi which extend into bronchioles and pulmonary alveoli. Bronchial Tree: Anatomy. Bronchitis is most frequently caused by a viral infection and presents with a self-limited cough.
• Heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR): a condition in which the heart is unable to pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols enough blood to meet the metabolic needs of the body. Heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR) can present with pulmonary edema Pulmonary edema Pulmonary edema is a condition caused by excess fluid within the lung parenchyma and alveoli as a consequence of a disease process. Based on etiology, pulmonary edema is classified as cardiogenic or noncardiogenic. Patients may present with progressive dyspnea, orthopnea, cough, or respiratory failure. Pulmonary Edema, causing dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea and cough.