Flashcards in Exam #4: Lower Respiratory Tract Infections I Deck (51):
What are the airway defenses against infection?
- Ciliated epithelium
- Mucociliary escalator
Thus, pathogens must circumvent mucociliary escalator & avoid being swallowed to cause disease (smoking, alcohol, narcotics--all impair the function of the mucociliary escalator)
What is bacterial pneumonia?
Inflammation of the lung parenchyma, accompanied by fluid accumulation (possibly purulent) in the alveoli that blocks gas exchange--caused by bacterial infection
What are the general features of pneumonia (symptoms)?
- Pleuritic chest pain
- Sputum production
What are physical exam findings indicative of pneumonia?
Rales (crackles) upon auscultation
*Note that this is common for typical pneumonia, but uncommon for atypical pneumonia
What is bacterial pneumonia normally secondary to?
Viral URT infections
Who is at increased risk for developing bacterial pneumonia?
- Those with comorbidities: heart disease, DM, lung disease/cancer, immunosuppresion
- Age extremes (infants & those older than 50)
- Smokers, alcoholics, & narcotic abuses--all of these impair the function of the mucociliary escalator
Describe the pathogenesis of bacterial pneumonia.
1) Bacteria enter small airways or alveoli and grow rich in lung environment
2) Virulence factors & immune response to bacteria produce local effects i.e. irritation, pain, & dyspnea
3) Accumulation of fluid, bacteria, neutrophils, and fibrin leads to consolidation or infiltrate seen on CXR
What is the difference between a lobar & patchy CXR?
Lobar= consolidation/ infiltrate
- Entire lobe is full, which is characteristic of "typical" pneumonia
- Bacteria grow in a web, which is a presentation of "atypical" pneumonia
What bacteria cause typical pneumonia?
- Strep. pneumoniae
- Staphylococcus aureus
- Haemophilus influenzae
- Most gram-negative bacteria
What bacteria cause atypical pneumonia?
- Mycoplasma pneumoniae
- Chlamydophila pneumoniae
- Legionella pneumophila*
Clinically, what are the features of a typical pneumonia? Specifically address: onset, presentation/ fascia, cough, sputum, fever, pleurisy, consolidation, WBC count & differential, CXR, & most common cause.
1) Sudden onset
2) Toxic presentation
3) Productive cough
4) Purulent sputum
5) Fever >103
6) Pleurisy is frequent
7) Consolidation frequent
8) WBC elevated (left shift) w/ leukocytosis (WBC increase)
9) CXR shows lobar pneumonia
10) Most commonly caused by Strep. pneumoniae
Clinically, what are the features of an atypical pneumonia? Specifically address: onset, presentation/ fascia, cough, sputum, fever, pleurisy, consolidation, WBC count & differential, CXR, & most common cause.
1) Gradual onest
2) Well Facies (i.e. walking pneumonia or non-toxic presentation)
3) Nonproductive cough
4) Sputum is scant/ watery
5) Fever less than 103 degrees
6) Pleurisy is rare
7) Consolidation is rare
8) WBC count is normal or slightly elevated
9) Patchy infiltrate seen on CXR
10) Most commonly caused by mycoplasma pneumoniae
What is a left band shift?
A left shift is an increase in the number of immature leukocytes in the peripheral blood, particularly neutrophil band cells
What does Legionella pneumophila cause?
Legionella is an atypical pathogen that cause a very severe presentation
What are the complications of pneumonia?
1) Pleural effusion or empyema (purulent effusion)
- Anemia with chronic pneumonia
- Disseminated intravascular coagulation
- Thrombocytopenia (reduction in platelet number)
3) Chronic complications
- Reduced arterial PO2
- Bronchiectasis (irreversible dilation of the bronchi & bronchiole)
What is an aspiration pneumonia?
Pneumonia caused by the introduction of foreign material into the lung
- Fluid carries bacteria in
- Large volume of fluid dilutes surfactant & prevents proper host immune response
What is aspiration pneumonia associated with?
What is CAP? What is HAP? How do the two differ?
CAP= "Community Acquired Pneumonia," any pneumonia not acquired in a healthcare setting
HAP= "Hospital Acquired Pneumonia," nosocomial pneumonia or pneumonia acquired in a health-care setting seen frequently in immunocompromised & ventilated patients
- Frequently caused by MDR Gram (-) bacteria
What is the differential diagnosis of pnemonia?
1) Hypersensitivity to drugs (edema in lungs)
2) Vasculitis of the lungs
3) Lymphoma/ carcinoma
What lab work is diagnostic for pneumonia?
1) CBC with elevated WBC count & left shift
2) Blood culture positive, which is indicative of severe disease
3) Sputum analysis showing less than 25 PMNs & less than 10 epithelial cells per 100x field is indicative of pneumonia
*Note that the majority of community acquired pneumonias are treated empirically based on clinical diagnosis & CXR
List the characteristics of streptococcus pneumoniae.
- Normal colonizer of the nasopharynx
- Gram (+) diplococci in chains
- Catalse negative (differentiates it from staph)
- Many serotypes (differentiated by capsular polysaccharides)
What are the pneumococcal virulence factors?
1) Surface adhesins that facilitate colonization of the pharynx
2) IgA protease that prevents clearance
3) Pneumolysin, an exotoxin that forms pores
4) Teichoic acid & Peptidoglycan that lead to inflammation
5) Thick polysaccharide capsule, which is anti-phagocytic
What is rust colored sputum indicative of?
How do you diagnose s. pneumoniae?
1) Gram stain sputum (Gram +)
3) Urine (tests for pneumococcal polysaccharide)
Specifically when culturing blood & sputum, what is indicative of s. pneumonaie infection?
1) Alpha-hemolysis on blood agar
2) Catalase neg.
3) Bile solubility positive
4) Optochin sensitive
How is s. pneumoniae treated?
3) Serious cases= azithromycin & caphalosporin
- Antimicrobial susceptibility testing for directed therapy
How is s. pneumoniae prevented?
List the characteristics of staph. aureus.
- Part of the normal microbiota in some individuals
- Gram (+) cocci in clusters
- Catalase pos.
- Coagulase pos.
What are the virulence factors associated with staph. aureus?
- Coagulase, which causes blood clotting
- Protein A, which binds the Fc-IgG of antibody; thus, is a form of antigenic mimicry + inhibits complement activation
- Panton-Valentine Leukocidin (PVL)
What is Panton-Valentine Leukocidin (PVL)?
A pore-forming cytotoxin that causes severe necrotizing pneumonia
What is MRSA?
Methicillin resistant staphylococcus aureus (MRSA)
- Bacteria that is resistant to all beta-lactam antibiotics
*Note that MRSA is not necessarily more virulent than other bacteria; rather, it is harder to treat
How is Staph. aureus pneumonia treated?
- Non-MRSA= PCN & cephalosporins
- MRSA= linezolid or vancomycin
Note that linezolid is a newer 50S bacterial ribosome inhibitor
What types of pneumonia are more commonly associated with gram (-) bacterial infection?
- Nosocomial/ HAP
- Aspiration pneumonia
What bacteria cause gram (-) pneumonia?
- Klebsiella pneumoniae
- Pseudomonas aeruginosa
*Others listed but not highlighted*
What are the characteristics of gram (-) pneumonia?
- Patient generally have an underlying disease
- Symptoms are typical
- Any lobe may be affected
- 0.25 have pleural effusion
- ABX resistance is a big problem
How is gram (-) pneumoia diagnosed?
1) Sputum culture & gram-staining
2) Blood culture
How is gram (-) pneumonia treated?
1) Broad spectrum antibiotics
2) Multiple drug therapy that is generally given IV
- Aminoglycoside + Beta-Lactam (Centamycin/ cephalaxein, tobramycin/ampicillin)
- Pseudomonas= Ticarcillin or piperacillin +amkacin
What are the characteristics of Klebsiella pneumoniae?
- Gram (-) rod
- Mucoid colonies (capsule)
- Strains commonly produce extended-spectrum beta-lactamases
- Oxidase negative
*Extended spectrum beta-lactamases impairs the function of the beta-lactam class of abx (PNC..etc.)*
What is the classic presentation of Klebsiella pneumoniae?
- Classic lobar pneumonia
with blood sputum from necrosis & abscess ( called "Currant jelly sputum")
What virulence factors are associated with klebsiella pneumoniae?
How is klebsiella pneumonia treated?
Same as other Gram (-) pneumonia i.e.
- Aminoglycoside + Beta-Lactam (Centamycin/ cephalaxein, tobramycin/ampicillin)
*Note that Kelbsiella pneumoniae has a 50% mortality rate even with treatment. Also, there is increasing abx resistance because of beta-lactamase*
How is kelbsiella pneumonia prevented?
- Disinfection of environment
- Use of sterile respiratory equipment
Describe the characteristics of pseudomonas aeruginosa.
- Gram (-) rods
- Obligate aerobe, which makes it sugar fermentation negative
- Oxidase positive
- Blue/ yellow pigment
- Culture smells like grapes
Where does pseudomonas aeruginosa typically grow?
- Water with minimal nutrients
- Hand soaps
- Dilute antiseptics
*Most strains form biofilms & typical sources of infection include humidifiers & respirator sink traps i.e. contaminated aerosols*
What other infections are associated with pseudomonas aeruginosa?
Think PSEUDOM (associated with wound & burn infections)
E= External otitis & Endocarditis
DO= Diabetic Osteomyelitis
M= Meningitis in patient's with extensive burns
Think pseudomonas in burn patients & CF.
What are the predisposing factors to pseudomonas infection?
2) Immunosuppressive therapy
3) Ventilator use
4) Cystic Fibrosis
What virulence factors are assocaited with pseudomonas?
- Toxin A= ADP-ribosylation of EF-2
- Leukocidin= pore-forming toxin that targets leukocytes
- PLC= membrane disruption
- Capsule= anti-phagocytic
- Pyocyanin= blue compound that is toxic to host cells
- Pyoverdin= flourescent green iron uptake protein
How is pseudomonas treated?
- Antipseudomonal penicillins i.e. ticarcillin or piperacillin
- Aminoglycoside i.e. gentamicin, tobramycin, amikacin
What is the most frequent cause of death in the CF population?
*Strains convert from non-mucoid to mucoid
What bacteria is currant-jelly sputum associated with?