APP 2 Chapitre 61 Flashcards
What are the five routes that pathogens can enter the respiratory tract?
1- direct inhalation
2- aspiration of upper airway contents
3- spread along the mucous membrane surface
4- hematogenous spread
5- direct penetration (rare)
Inhalation and aspiration most common +++
Hematogenous spread and direct penetration are rare, but important infection of lung parenchyma
What are the defense mecanisms of the respiratory tract? Difference between large and small particles?
1- In the nose specialized hairs, known as vibrissae, filter large particles suspended in inhaled air. Large particles (>10 μm in diameter) tend to settle at points where abrupt changes in the direction of airflow occur, such as the posterior nasopharynx. Smaller particles (<3 μm in diameter) are likely to elude those barriers and reach the terminal bronchioles and alveoli. (Aerodynamic factor)
2-The structure of the larynx and the cough reflex provide protection against gross aspiration of upper airway and gastric contents, preventing transmission of associated bacteria to the lower respiratory tract. (The epiglottis and cough reflex prevent introduction of particulate matter into the lower airway)
3-Epithelial cells from the nose to the terminal bronchioles are covered with cilia that beat coordinately.
4-Overlying these cilia is a covering of mucus containing antimicrobial compounds such as lysozyme, lactoferrin, and secretory IgA antibodies. The mucus traps foreign particles, including pathogens. The cilia move the overlying mucus layer upward toward the larynx; together, they are called the mucociliary escalator.
Many patients with impaired ciliary function have frequent respiratory infections that ultimately lead to bronchiectasis (permanent abnormal dilation of the small airways).
5-The final lung defenses are found in the alveoli. The alveoli contain IgA antibodies, complement components, and, most importantly, alveolar macrophages.
These phagocytic cells function as active scavengers, ingesting and killing invading pathogens. When they cannot contain infection by themselves, they are helped by other phagocytic cells that do not normally reside in the lungs, especially neutrophils. Macrophages and neutrophils are especially important in fighting bacterial infections. In viral infections, histopathological studies of the lungs (or other affected tissues) show infiltration by large numbers of lymphocytes and plasma cells, suggesting that viral infection stimulates recruitment of lymphoid cells rather than neutrophils. Lymphocytes contribute to host defense by producing antibodies and attacking infected cells through cytotoxic T lymphocytes, natural killer (NK) cells, and antibody-dependent cell-mediated cytotoxicity (ADCC).
F., a 5-year-old boy who had been in good general health, was brought to the pediatrician because of fever and sore throat that began 2 days earlier. On examination, F. had a temperature of 38.3 °C. His oropharynx was erythematous. His tonsils were enlarged and coated with patchy white exudates. His anterior cervical lymph nodes were also enlarged and tender. The remainder of the examination was unremarkable. A rapid antigen detection test (RADT) was positive for group A streptococcus. F. was treated with intramuscular penicillin, and his symptoms resolved over the next week. This case raises two questions:
1- What organisms commonly cause pharyngitis?
2- Why is it important to distinguish streptococcal pharyngitis from other forms of the disease?
1-
Group A streptococcus, respiratory viruses, Epstein-Barr virus, and Chlamydia pneumoniae cause pharyngitis.
2-
Streptococcal pharyngitis can lead to pyogenic complications like peritonsillar and retropharyngeal abscesses and immunological complications like glomerulonephritis and rheumatic fever.
What is the most common cause of bacterial pharyngitis?
Group A streptococcal pharyngitis
Who is Group A streptococcal pharyngitis most commonly seen in?
In school-aged children during the winter
True or false respiratory viruses as a group are the most common cause overall?
True
What symptoms decrease or increase the likelyhood of Streptococcus group A?
Increase:
Fever
Tonsillar exudates
Tender cervical adenopathy
Decrease:
Conjunctivitis
Cough
Coryza
That said, no clinical features are diagnostic for a specific pathogen, and it can be difficult to differentiate between viral and bacterial pharyngitis on the basis of clinical findings.
How to we detect streptococcus group A?
.Unless viral symptoms are predominant, a rapid antigen detection test (RADT; see Fig. 57-6) should be performed to detect group A streptococci. In children, negative RADT = prompt a culture (high prevelance group A and risks of complications) because RADTs are not as sensitive. However, in adults not needed culture (less risks).
What are the complications associated with group A streptococcus?
-Peritonsillar and retropharyngeal abscesses
-Otitis media
-Sinusitis
-Pneumonia
-Acute glomerulonephritis
-Rheumatic fever
Common pathogens of each area?
What respiratory viruses frequently cause pharyngitis?
- Rhinoviruses,
-adenoviruses,
-coronaviruses, - influenza viruses
- parainfluenza viruses
The presence of conjunctivitis suggests infection by adenovirus,
while coxsackieviruses—especially the group A coxsackieviruses—sometimes produce small vesicles on the mucous membranes of the throat, a clinical picture known as herpangina.
In the adolescent and young adult age group, Epstein-Barr virus is a common cause of pharyngitis, one of the manifestations of infectious mononucleosis. It is also important to consider acute HIV in patients with risk factors.
Most common pathogens for pharyngitis?
Part 2 most commin pathogens for pharyngitis?
True or false often in patients with pharyngitis, a pathogen is not identified?
True
Infections of the nasopharynx are generally caused by viruses and give rise to the signs and symptoms known collectively as the common cold. Approximately 30%-50% of colds are caused by the rhinovirus group (see Chapter 34). Coronaviruses are the next most common group of agents, accounting for ~7%-18% of colds before the emergence of SARS-CoV-2, which in mild cases can manifest in this way. The agents of the remaining percentage of colds are various respiratory viruses, including parainfluenza viruses, respiratory syncytial virus (RSV), influenza viruses, adenoviruses, and metapneumoviruses (see Chapters 32, 33, and 34). Although the patient with a cold may experience a “scratchy” throat, nasal symptoms are usually more prominent, including cough caused by postnasal drip. Bacterial infection of the nose occurs occasionally but is not common.
Non–group A β-hemolytic streptococci
Account for a small proportion of cases, as do gonococci in sexually active individuals.
