Upper Respiratory Tract Infections

Upper Respiratory Tract Infections

• The respiratory tract divides into upper and lower regions
• The upper respiratory tract includes the epiglottis, surrounding tissues, larynx, nasal cavity, and pharynx (throat)
• The pharynx is a muscular, tubelike structure from the base of the skull to the esophagus split into three parts
  • Nasopharynx which is the portion of the pharynx above the soft palate
  • Oropharynx, the portion of the pharynx between the soft palate and epiglottis
  • Laryngopharynx, the portion of the pharynx below the epiglottis that opens into the larynx
• The oropharynx and nasopharynx are lined with stratified squamous epithelial cells filled with microbial flora
• Tonsils are contained within the oropharynx
• The larynx is located between the root of the tongue and the top of the trachea

Upper Respiratory Tract Infections (URIs)

• URIs occur when viruses or bacteria infect any part of the upper respiratory tract
• The upper respiratory tract consists of: the nose, sinuses, pharynx, trachea, and bronchi
• URIs are the areas through which air enters the body and travels to the lungs
• URIs can be very serious because they can spread to the lungs
• Most URIs are caused by viruses, so are not treatable with antibiotics
• The two most common URI viruses are the common cold (rhinovirus) and influenza (the flu)
• URI symptoms are caused by an allergic reaction to the infection itself

Pathogenesis

• URIs can spread and become more serious because the upper tract's mucosa is continuous with the mucosal lining of the sinuses, eustachian tube, middle ear, and lower respiratory tract
• Diseases of the upper respiratory tract are named according to the anatomic sites involved
• Most URIs are self-limiting, and most are caused by viruses
• Viruses enter host cells through specific viral surface proteins
• This causes tissue injury, resulting in clinical disease

Viral and Bacterial Interactions

• Specific bacterial-bacterial and viral-bacterial interactions occur in the upper respiratory tract
• Respiratory infectious diseases are mainly caused by viruses or bacteria that interact
• Viruses and bacteria may be present in the nasopharynx without causing respiratory symptoms, but are a prerequisite for secondary infections
• The upper respiratory tract hosts a vast range of commensals and potential pathogenic bacteria, forming a complex microbial community that are subject to synergistic and competitive interspecies interactions
• Disturbances in the equilibrium may lead to overgrowth and invasion with new viruses or bacteria

Relationship to Disease

• Colonization of the upper respiratory tract not only causes disease but also drives the evolution of opportunistic pathogens
• To cause respiratory disease, bacteria must colonize the nasopharyngeal niche
• Colonization of this niche is a dynamic process with
  • Acquisition and elimination of species
  • Interactions among microbes and between microbes and the host
  • Interference by environmental factors
• Viral and bacterial species interplay is a crucial first step in respiratory and invasive diseases

Laryngitis

• It is an inflammation of the larynx that is related to upper respiratory tract infections
• Acute laryngitis is associated with the common cold or influenza syndromes
• Patients typically complain of hoarseness, as well a lowering or deepening of the voice
• Acute laryngitis is generally a benign illness by viruses
• Numerous viruses can cause laryngitis include
  • Influenza, Parainfluenza viruses
  • Rhinoviruses, Adenoviruses
  • Coronavirus and human metapneumovirus
• Streptococcal infection, mononucleosis, or diphtheria should be suspected if an exam reveals exudate or membranes covering the tissues of the upper respiratory tract

Laryngotracheobronchitis (Croup)

• It is closely related to laryngitis
• It is relatively common in young children, primarily those younger than 3 years of age
• The infection can extend downward and involve the trachea or even the bronchi, representing a more serious disease
• Viruses are a primary cause; Parainfluenza viruses are the major etiologic agents
• Influenza viruses, respiratory syncytial virus, and adenoviruses can cause croup

Epiglottitis

• An infection of the epiglottis which causes edema (swelling) and inflammation
• A potentially life-threatening disease because it can cause complete obstruction of an infected patients airway
• Caused by bacteria, particularly Haemophilus influenzae type b was the primary cause, however cases are also credited to streptococci and staphylococci
• Epiglottitis involves the epiglottis that swells, blocking the flow of air into lungs
• The patient presents with a bright red epiglottis
• Swabbing of the epiglottis can lead to respiratory obstruction, and bacteriological culture is contraindicated
• H. influenzae bacteremia commonly occurs

Pharyngitis

• Commonly called a sore throat
• Tonsillitis is the inflammation of the tonsils
• Is associated with pharyngeal pain
• Characterized by the inflammation of the pharynx at the back of the throat
• Visualization shows the affected tissues are erythematous (red) and swollen
• Inflammation may result in inflammatory exudates, vesicles, mucosal ulceration, or nasopharyngeal lymphoid hyperplasia (swollen lymph nodes)
• Most organisms directly invade the pharyngeal mucosa, others elaborate toxins and other virulence factors at the site
  • Arcanobacterium haemolyticum is an invader
  • Corynebacterium diphtheriae, an elaborator of toxins
  • A. Haemolyticum is a gram-positive bacillus
  • Group A streptococci [Streptococcus pyogenes] also invade and elaborate factors

Symptoms of Bacterial Pharyngitis

• A sore throat is the primary symptom caused by inflammation of the throat
• Caused by an infection of group A Streptococcus bacteria.
• Viral infections are most common, however infectious microorganisms or non-infectious agents can cause pharyngitis

Common Virus Types

• Influenza is a common viral example causing a sore throat
• Group A Streptococcus (GAS, Streptococcus pyogenes or β-hemolytic group A Streptococcus) is the most common bacterial cause
• Colds or the flu are the most common causes of pharyngitis
• Corynebacterium, gonorrhea, and chlamydia can cause a sore throat, but less commonly
• Pharyngitis typically comes on during colder months

Treatment, Causation, and Effect

• Primary cause of bacterial pharyngitis is Streptococcus pyogenes (or group A beta-hemolytic streptococci)
• Must be differentiated from viral pharyngitis because S. pyogenes pharyngitis is treatable with penicillin, and viral infections are not
• Infection with pyogenes can lead to complications such as acute rheumatic fever and glomerulonephritis

Epidemiology and Treatment

• The illnesses often occur in the colder months
• Respiratory tract infections may be caused by influenza types A and B, parainfluenza, coxsackie A, rhinoviruses, or coronaviruses
• Patients complain of a sore throat.

Bacterial Infection

• Most cases are caused by common respiratory viruses, can be usually self-limited, with no treatment needed
• Bacteria are also important etiologic agents that can be treated with antibacterials
• Swabbing the throat and testing for pyogenes should be performed since clinical features can not reliably distinguish GAS pharyngitis from viral pharyngitis
• When patients present covert, obvious, and observed clinical signs of viral infection they are exceptions

Presentation of Streptococcal Infections

• May appear as pharyngitis (strep throat), scarlet fever (rash), impetigo or cellulitis
• Patients may develop immune-mediated post-streptococcal sequelae, such as acute rheumatic fever and acute glomerulonephritis
• Pyogenes produces virulence factors and diseases
• Acute rheumatic fever (ARF) is a sequela of streptococcal infection involving an autoimmune response to a bacterial infection

Streptococcus pyogenes Infections

• Virulence factors of Group A streptococci include M protein, Protein F, lipoteichoic acid, hyaluronic acid capsule, invasins, and exotoxins
• pyogene is a pathogen due to its ability to colonize, rapidly multiply, and spread while evading phagocytosis and confusing the immune system
• Acute diseases occur in the respiratory tract, bloodstream, or skin
• Streptococcal disease is often a respiratory infection (pharyngitis or tonsillitis) or a skin infection (pyoderma)
• pyogenes commonly causes uncomplicated bacterial pharyngitis and tonsillitis and is referred to as strep throat

Complications

• S. pyogenes uses lipoteichoic acid and hyaluronic acid to adhere to the pharyngeal epithelium
• Poststreptococcal sequelae is mainly mediated by immunologically
• S. pyogenes may also cause pyogenic infections of the tonsils, sinuses, and middle ear, or cellulitis as secondary pyogenic sequelae after an episode of pharyngitis
• Cases of caused by groups C and G and by nonhemolytic members of these groups of streptococci (including group A) have been reported.
  • S. pyogenes (group A Streptococcus, GAS) is a human-adapted pathogen

Different Forms of Pharyngitis

• Is caused by bacteria other than group A streptococci
• Group C streptococci are similar to S. pyogenes and present similar symptoms
• beta-hemolytic groups C and G streptococci diseases share resemblance to strep infections
• streptococci can use information to exchange with each other potentially becoming superantigen or similar
• GAS pharyngitis is the known cause for majority of community bacterial adhesion

Nasopharyngeal and Throat Cultures

• H. influenzae, S. aureus, and S. pneumoniae may be isolated, but have not been shown to cause pharyngitis
• The bacterial infection is attributed to Corynebacterium diphtheriae, Fusobacterium necrophorum, and Neisseria gonorrhoeae
• Viral pharyngitis may be caused by non-bacterial influenzas, EBV, HIV
  • Fusobacterium necrophorum is also a known cause and produces an anaerobic, non-spore forming pleomorphic Gram-negative rod
• Rhinitis characterized with typical common cold can be caused bacterial infection

Agents that cause Pharyngitis

• Streptococcous pyogenes is the most frequent.

Corynebacterium diphtheriae

• Less common than streptococcal, can still be isolated
• Diphtheria occurs after 2-4 days from incubation, presents with pharyngitis and tonsilitis
• An exudate of membrane develops on the tonsils and pharyngeal wall as evidence
• Results characterized by sore throat, adherent membrane with low fever, and an upper respiratory tract illness
• The presence of the bacterium is diagnosed by a swab or seroligics

Bordetella pertussis

• Whooping cough is a respiratory disease that is highly contagious, caused by the bacterium bordetella pertussis
• Marked by paroxysmal coughing that makes it hard to breath
• Symptomatic infections from infections appear after 7-13 days
• Bordetella petussis releases a gram-negative bacteria

Action of B. Pertussis

• Damaging lipopolysaccharide in the cell wall of the respitory system
• Quickly adherse to multiply on the trachea that irritates cells and causes coughing
• B. pertussis has a pathogenicity that has a variety of factors and can lead necrosis in parts of the epthelium and pneumonia
• Bacterial culture needs to be performed first with nasopharyngeal specimens during the initial 2 weeks

Stomatitis

• Is the inflammation of mucous membrane
• Herpes simplex virus is the cause of multiple ulcerative lesions
• Oral cavity infections are prone for immunocomprimised patients to infect
• Yeast such as Candida species can cause infections as well

Periodontal Infections

• Often due to improper or insufficient oral hygiene, can cause tooth loss
• Oral bacteria have an adverse impact as well in terms of mineralized tissue

Links to Systemic Disease

• Host Microbe infections can potentially lead to microbial infections like with the gums, gingivitis/osteoporosis and cause reduced protection

Periodontal Disease

• Destruction of hard tissue in result of improper care can be caused in either gingivitis or with periodontitis where gum tissue and bone deteriorates

Periodontitis and Dental Plaque

• Infections may occur in gums tissues and cause the body to destroy/inflame it
• The more bacterial infections, the higher changes are of a portal bacteria spreading
• These infections usually are from biofilm

Periodontal Disease

• A condition of the teeth affected by improper plaque build up with bacteria that the infection causes is commonly treatable
• Bacteria can easily start spreading throughout the entire body

Divisions and causes of Periodontal Disease

• Lesions can cause infections at many gum illnesses, or can occur from bacterial parotitis

Diseases of The Neck

• Infections can spread from deep tissue in the neck
• It has been associated with gram-negative bacterial infections with oral flora