Transcript Respiratory Infections

Respiratory Infections
T. Davis
9-22-2014
OBJECTIVES
• Discuss the pathogenesis of specific respiratory
infections
• Describe the pathologic features of specific
respiratory infections
• Know how infectious diseases of the respiratory
tract are diagnosed in the laboratory
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EXAMPLE QUESTION
ICAM-1 serves as the receptor for attachment of
A. Mycobacterium tuberculosis
B. Influenza viruses
C. Haemophilus influenzae
D. Rhinoviruses
E. Histoplasma capsulatum
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Intro: Respiratory Tract Infections
• Community acquired pneumonia is common
– 5.6 million people (est.) annually in US resulting in 1.3
million hospital admissions per year
– And in those over age 65, the number one cause of
death from infectious diseases
• Nosocomial (hospital acquired) pneumonia is the
leading cause of death from infection in US
hospitals; its occurrence prolongs hospital stays
about 8 days
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Rhinoviruses
• 60% of common colds due to rhinoviruses: other
causes = coronavirus 15% (also is agent of SARS*),
influenza virus, parainfluenza virus, respiratory
syncytial virus (RSV), adenovirus, & enterovirus (110% of colds)
• Rhinoviruses: picornavirus family (small RNA viruses
with single stranded RNA genome)
• Rhinovirus binds intercellular adhesion molecule
(ICAM-1) on respiratory epithelial cells & induces
mucus secretion via bradykinin release
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Enterovirus 68
• Close relative to Rhinoviruses
• Clusters in U.S. since 1960s- this summer
hundreds of new cases
• “enterovirus season” in late summer
• Children <5; asthma
• Supportive treatment
• We ID rhinovirus/enterovirus- typing at St.
Bd. Or CDC
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Influenza Viruses
• Single-stranded RNA
• Types A, B, or C
• Subtypes (H1 - H3: N1 or N2) determined by viral
hemagglutinin & neuraminidase in lipid envelope
– eg., H3N2
• Viruses are spread person to person by airborne
droplets or contact with contaminated hands or
surfaces
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Influenza Viruses
• Epidemics through mutations of hemagglutinin (H)
& neuraminidase (N) that allow virus to escape
host antibodies
– Antigenic drift: minor antigenic change due to point
mutations
– Antigenic shift: major antigenic change (both H and N
replaced) due to genetic reassortment between animal
& human influenza A viruses (but not B or C)
• Pandemics due to novel influenza viruses: 1918,
1947, 1957, 1968, 1968, 1977, and 2009
– 1918 Spanish flu killed 20-40 million world wide
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Influenza: More Characteristics
• Clearance of infection - occurs when
cytotoxic T cells kill virus-infected cells
• Host antibodies to H and N prevent future
infection with that specific virus
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Influenza: More Characteristics
• Lab dx: swab of nasopharynx, throat swab, combined
nose/throat swab, nasal washes, or bronchial lavages
– virus isolation/culture – gold standard but takes 3-7 d
– viral Ag detection by direct FA (fluorescent antibody);
– multiplex RT-PCR (reverse transcription PCR); more sensitive;
but slower than FA; takes overnight
– Rapid Ag point-of-care tests are the least sensitive/false negs;
takes 15 min
• Rx: Tamiflu (oestelamivir) and Relenza (zanamivir)
effective in 1st 24-48h vs influenza A (neuraminidase
inhibitors of both influenza A & B)
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Autopsy findings in lungs of a patient who died
(in Fall of 2009) with H1N1/09
Routes By Which Bacteria
Get Into Lungs
• #1 is Aspiration of contaminated oropharyngeal
contents
(e.g. pneumococci, GNRs, anaerobes)
• Inhalation (M. tuberculosis, Legionella, plague)
• Bacteremia
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Factors That Predispose
To Bacterial Pneumonia
Age (extremes)
Alcohol
Anesthesia
Bone marrow transplant
Cerebrovascular illness
Chemotherapy;
immunosuppression
Chronic obstructive
pulmonary disease
Cigarette smoking
Cirrhosis
Cystic fibrosis
Debility in general
Edema; congestion (CHF)
Immune deficiencies
Malignancy
Obstruction
Splenic dysfunction
Ventilator use
Viral infections
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Community-Acquired Pneumonia: Pathogens
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Streptococcus pneumoniae
Haemophilus influenzae
Moraxella catarrhalis
Staphylococcus aureus
Legionella spp.
Enterobacteriaceae (e.g., Klebsiella
pneumoniae)
• Pseudomonas aeruginosa
• Viruses, Mycoplasma, Chlamydophila
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Hospital-Acquired Pneumonia
• Staphylococcus aureus: MRSA > MSSA
• Gram-negative rods
– Enterobacteriaceae (Klebsiella spp., Escherichia
coli, and others)
– Pseudomonas aeruginosa, Stenotrophomonas
maltophilia, Acinetobacter spp.
• Legionella spp.
• Anaerobes (aspiration)
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Morphology of Bacterial Pneumonia
• 2 frequently overlapping GROSS
morphologic patterns
– Bronchopneumonia
– Lobar pneumonia
• Caused by a variety of gram-positive and
gram-negative bacteria
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Comparison of Bronchopneumonia and
Lobar Pneumonia
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In both lobar- and bronchopneumonia alveoli are filled with
neutrophils
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Lobar pneumonia
• Diffusely involves large portion of lobe or entire lobe
of lung
• Encapsulated bacteria spread alveolus-to-alveolus
through pores of Köhn
• Most common cause = pneumococcus
(Streptococcus pneumoniae), but occas. Klebsiella
pneumoniae, staphylococci, streptococci, H.
influenzae
• “
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Lobar Pneumonia
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Complications of Lobar
Pneumonia
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Abscess
Pleuritis and empyema
Organizing pneumonia (leaves residual fibrosis)
Bacteremia and sepsis
Infarct
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Laboratory Diagnosis of Pneumonia
• Sputum specimen collected and sent to lab
• Direct smears for Gram stain
• Specimen cultured on various media
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Diagnosis of Pneumonia due to
Streptococcus pneumoniae
– Gram-stained sputum containing many neutrophils
and typical gram-positive, lancet-shaped
diplococci supports diagnosis of pneumococcal
pneumonia; alpha-hemolytic colonies
– But remember, S. pneumonia is part of oropharyngeal
microbiota in 20% of adults
– Its isolation from blood cultures is more specific but
less sensitive than sputum culture; only 25-30% of
patients have positive blood cultures
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Streptococcus pneumoniae:
Sputum Gram Stain
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Klebsiella pneumoniae
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Mucoid, encapsulated K. pneumoniae
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Infections with Haemophilus
influenzae
• Respiratory
– Life threatening epiglottitis - submucosal
inflammatory edema may obstruct airway < 24h
after onset; generally children 2-4 yrs
– Otitis media, chronic bronchitis, bronchopneumonia
– Pathology: dense fibrin-rich exudates of neutrophils
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Acute Otitis Media
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Haemophilus influenzae:
Acute Purulent Bronchitis
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Diagnosis of H. influenzae Infection
• Tiny gram-negative coccobacilli in gram-stained
smears of sputum or CSF
• Culture on chocolate agar - requires X & V factors
for growth
• Rapid I.D. -- e.g., latex agglutination or DNA probe
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Haemophilus influenzae: Gram-Negaitve
Rods in Sputum
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Bronchopneumonia
• Patchy exudative consolidation of lung
parenchyma (airway spread)
• Gross: dispersed, elevated, focal firm areas
• Microscopic: acute neutrophilic suppurative
exudate filling air spaces and airways at level
of bronchi and bronchioles
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Pseudomonas aeruginosa Infection
• P. aeruginosa necrotizing
pneumonia
• With necrotizing vasculitis
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Staphylococcal Infections
Staphylococcus aureus
• Gram-positive cocci;
grape-like clusters
• catalase and coagulase
• Acute (“pyogenic”)
inflammation, often with
abscesses
• Abscess def: “localized
collection of pus in a cavity
formed by disintegration of
tissues”
Pathogenesis:
What Makes S. aureus So Virulent?
• Catalase. H2O2 to H2O probably counteracts PMN killing
by splitting toxic oxygen radicals
• Coagulase. Converts fibrinogen to fibrin (?? WBCs
penetrate fibrin poorly??)
• Hyaluronidase. Hydrolyses connective tissue matrix
• -lactamases. Hydrolyse -lactam antibiotics
• Leukocidin. Makes pores in membranes of PMNs (eg.,
Panton-Valentine leukocidin [PVL])
• Methicillin-resistant SA (MRSA)- mecA gene codes for
changes in cell wall proteins (PBPs)
Staphylococcus aureus virulence factors
continued
• Toxic Shock; was originally associated with
hyperabsorpent tampons that became colonized with S.
aureus during use; TSS can also be caused by S. aureus
in infected surgical sites.
– hypotension (shock), renal failure, coagulopathy, liver
disease, respiratory distress, generalized erythematous
rash, & localized tissue necrosis
– Note: TSS can also be caused by Streptococcus pyogenes
• Food poisoning; Superantigens produced by S. aureus
also cause vomiting
• **food poison in 4 hours: S. aureus or Bacillus
cereus
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Staphylococcal
pneumonia
Recent Case - Frozen Section:
RLL Abscess/ Low power H&E
Higher power H&E
Methicillin Resistant Staphylococcus
aureus (MRSA)
 Healthcare-Associated
 (HA-MRSA): HIGHLY RESISTANT
(all beta-lactams & multiple other
antimicrobials)!
 Nursing Homes,Nosocomial
 Requires isolation of patients
 50-60% of hospital SA
 Community-Associated
 (CA-MRSA): often resistant to
only beta-lactam agents &
erythromycin; treat with Septra,
Clindamycin
 CA-MRSA have become the most
frequent cause of skin & soft tissue
infections
 75-90% of community SA
Laboratory Identification
Staphylococcus aureus is
COAGULASE POSITIVE.
The other > 30 species of
Staphylococcus (eg., S.
epidermidis, & S.
saprophyticus) are
COAGULASE NEGATIVE.
Slide Coagulase Test
Coagulase: ProthrombinLike Substance Able to Clot
Human or Rabbit Plasma.
Tube Coagulase Test
Negative
(Positive)
CATALASE TEST
H2O2
H2 + O2 (bubbling)
Slide catalase
Genus Staphylococcus is Catalase Positive
Genera Streptococcus & Enterococcus are
Catalase Negative
Streptococcal Infections (Group A)
• Gram + cocci in pairs or
chains
• Beta-hemolytic
• Infections include “strep.
throat”, tonsillitis, erysipelas,
impetigo, cellulitis, wound
infections, scarlet fever,
necrotizing fasciitis,
septicemia, & pneumonia.
Group A Strep. pharyngitis & tonsillitis (the major
cause of poststreptococcal rheumatic fever and
glomerulonephritis [also follows skin infections])
Why is Group A Strep. so
Virulent?
• M–protein
• M+ strains = resistant to phagocytosis
• Erythrogenic Toxin (Pyrogenic Exotoxin)
• rash of scarlet fever
• Streptokinase/fibrinolysin (breakdown fibrin)
• Spreading infections, e.g. cellulitis, erysipelas
• Hyaluronidase (breaks down ground substance)
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Spreading infections
Bacterial Meningitis
Common Pathogens
•Neonates: S. pneumoniae and Escherichia coli; no longer
Group B strep
•Children & young adults 2-29 yrs: Neisseria meningitidis
60%, S. pneumoniae 27%
•Adults 30 -to- > 60 yrs: S. pneumoniae 61%, N. meningitidis
18%, H. influenzae 12%, L. monocytogenes > 2%
Clinical
•Patients show fever, headache, photophobia, irritability,
altered mental status, neck stiffness
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Usual Sequence for Severely Ill
Patients with Suspected Bacterial
Meningitis
• Stat empiric antibiotics (e. g., if 2-50 yo,
vancomycin + ceftriaxone or cefotaxime)
• CT scan if needed
• Lumbar puncture (LP)
• Cerebrospinal fluid (CSF): typical results OP >30
cm (nl <17 cm), WBC >500 cells/ml with >80%
neutrophils, glucose <40 mg/dL (or <2/3 plasma),
& protein >200 mg/dL; gram stain usually shows
bacteria
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Neisseria meningitidis
• Capsule dictates 13 serogroups
• Usual pathogenesis: oropharynx (carriage/infection)
then bacteremia and/or fulminant meningococcemia
• Causes meningitis, septicemia, disseminated
intravascular coagulation, and WaterhouseFrederichson syndrome with acute hemorrhagic
infarction of adrenals
• Remember: young adults – most common age
group (army barracks, college dormitories,
camps, etc)
• Diagnosis by Gram’s stain & culture: blood, CSF
N. meningitidis in CSF (note mostly extracellular location)
Neisseria meningitidis on CHOC
Diagnosis of H.influenzae
Infection
• Tiny gram-negative coccobacilli in gram-stained
smears of CSF or upper respiratory specimens
• Culture on chocolate agar; unsupplemented
sheep blood agar unsuitable for H. influenzae
• Requires X & V factors for growth
• Rapid I.D. -- e.g., latex agglutination or DNA
probe
Haemophilus on CHOC (creamy colonies)
Pleomorphic GNRs of Haemophilus in CSF
Infections
By Anaerobic
Bacteria
Some Examples of Clinically Significant
Anaerobe Infections
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Brain abscess
Actinomycosis
Anaerobic dental/oral infections (Vincent’s disease)
Anaerobic pleuropulmonary infections: aspiration
pneumonia, abscess, thoracic empyema
• Intraabdominal sepsis
• Gas gangrene
• Non-clostridial crepitant cellulitis
Major Anaerobes Encountered in
Aspiration Pneumonia
• Bacteroides fragilis group
• Pigmented Prevotella/Porphyromonas
group
• Fusobacterium spp. (e.g., F. nucleatum)
• Peptostreptococcus spp. (the anaerobic
cocci)
• Actinomyces (e.g., A. israelli)
Actinomyces
fistula
“lumpy jaw”
Sulfur granule on Gram Stain
Actinomyces vs Nocardia in
Pulmonary Specimens
Actino
Gram +
Nocardia
Gram +
Branching
filaments
Actino:
(not acidFast)
Nocardia;
ModifiedKinyoun
(acid-fast)
Anaerobic
Aerobic
Tuberculosis
(Mycobacterium tuberculosis)
• Epidemiology: kills > 3 million per year; #1 cause
of death worldwide due to any infectious agent
• Acid-fast bacilli – red with blue background
• Slow-growing aerobes (14-28 days!)
• Spread mostly by aerosolized droplets
• Can involve virtually every organ, most importantly
lungs
• Typically associated with granuloma formation
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Acid-fast bacilli of Mycobacterium tuberculosis
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Cell Wall Virulence Factors
• Cord Factor: glycolipid that causes TB to grow in
serpentine cords
– more virulent strains
• Lipoarabinomannan (LAM): polysaccharide
similar to endotoxin
– inhibits macrophage activation by interferon-
– also induces macrophages to secrete
TNF- (causes fever, weight loss & tissue damage),
& IL-10 which suppresses T-cell proliferation
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“cording” of M. tuberculosis
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Host Factors
• Infants and elderly more susceptible
• Socioeconomic factors more important than
ethnic/racial factors
• Relative risk for U.S. non-whites is 10X the
risk for whites
• Relative risk for homeless
(white or non-white) is 150X higher
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Predisposing Diseases
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Diabetes mellitus
Alcoholism or malnutrition
Chronic lung disease, esp. silicosis
Immunosuppression, esp. AIDS
• (Any debilitating or immunosuppressive
condition)
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Primary Tuberculosis
(1st infection with TB - no prior
exposure)
1. Mid lung field granuloma (Ghon lesion)
2. Hilar lymph node granuloma
These two form what is termed the Ghon
complex – found in 95% of primary TB.
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Primary Tuberculosis
(1st infection with TB - no prior
exposure)
3. Miliary TB or Hematogenous spread
pulmonary artery – lung
pulmonary vein – systemic
4. Cavitary TB
5. Chronic pulmonary infection
These last three make up 5% of primary TB.
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LN
Ghon Lesion
Ghon Complex or Promary Complex (LN and peripheral lesion)
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T-Cells in Tuberculosis
• CD4+ helper T cells secrete interferongamma, which activates macrophages to kill
intracellular TB via reactive nitrogen
intermediates (NO, NO2) and is associated with
epithelioid cell granuloma formation and removal
of TB
• CD8+ suppressor T cells kill macrophages
that are infected with TB, resulting in formation of
caseating granulomas (delayed-type
hypersensitivity rxns)
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Epithelioid (L) & Caseating (R) Granulomas
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Miliary Tuberculosis
• Hematogenous spread to many organs
• Tiny yellow-white granulomas resemble millet
seeds
• Via pulmonary artery to lungs
• Via pulmonary veins to bone marrow, liver,
spleen, kidney, adrenals, prostate, heart
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Secondary Tuberculosis (rare)
• May occur one year or 50 years after
primary TB, i.e. anytime!
• Two varieties:
– Reactivation TB (95%)
– Reinfection TB (5%)
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Secondary Tuberculosis (rare)
1. Apices of lung
2. More necrosis, less lymphatics
3. Miliary TB
4. (More) cavitary
likely because of additional necrosis
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“TB or not TB?”
• Direct acid-fast stain on sputum or tissue
• Culture in liquid Middlebrook medium (7-10 days)
• Direct amplified probe on sputum identifies M.
tuberculosis and resistance gene to Rifampin
• PPD and Interferon-gamma tests on lymphocytes
(more sensitive and more specific)
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Histoplasmosis
(Histoplasma capsulatum)
• Epidemiology
– dimorphic fungus
– found in Indiana and along Ohio and Mississippi Rivers
– acquired by inhalation of dust from soil
contaminated with bird or bat droppings (think of who
might be at risk)
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Histoplasmosis
• Granulomatous disease
– intracellular 2-4 µm yeasts
• Clinical presentations & anatomic pathology
are strikingly similar to tuberculosis
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H. capsulatum in macrophages
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GMS shows small budding yeast of H. capsulatum
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Coccidioidomycosis
(Coccidioides immitis)
• Epidemiology
– dimorphic fungus
– especially common in southwest/western US and
Mexico
• Acquired by inhalation of infective arthroconidia
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Coccidioidomycosis
• Granulomatous disease that resembles
tuberculosis
• Pathology
– 20-60 µm spherules filled with endospores in
sections of lung lesions or other anatomic sites
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Blastomycosis
• Blastomyces dermatitidis
• Ohio River Valley plus KY, NC, WI
• Pulmonary disease after inhaled conidia with
spread to other sites
• Tissue phase is a large (10-12 microns) yeast with
a thick cell wall and broad-based-budding
• Pseudoepitheliomatous hyperplasia mimics
cancer in skin and larynx
Pseudoepitheliomatous hyperplasia in blastomycosis
Broad-based budding in blastomycosis
Ebola Virus
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Known since 1970s
Vomiting, diarrhea, rash
Renal and hepatic failure
Hemorrhage
Contact with blood or body fluids
Droplets and not aerosols??
Mortality 50%+
Dx at CDC
Level 4: negative pressure rooms and
“spacesuit”
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