Respiratory Infections

T. Davis9-22-2014

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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 (1-10% 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

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)

Autopsy findings in lungs of a patient who died (in Fall of 2009) with H1N1/09

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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) Cystic fibrosisAlcohol Debility in generalAnesthesia Edema; congestion (CHF)Bone marrow transplant Immune deficienciesCerebrovascular illness MalignancyChemotherapy;

immunosuppression ObstructionChronic obstructive

pulmonary disease Splenic dysfunctionCigarette smoking Ventilator useCirrhosis Viral infections

Community-Acquired Pneumonia: Pathogens

• 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

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

• 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

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

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

Pseudomonas aeruginosa Infection

• P. aeruginosa necrotizing pneumonia

• With necrotizing vasculitis35

Staphylococcal InfectionsStaphylococcal InfectionsStaphylococcus 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:Pathogenesis: What Makes What Makes S. aureus S. aureus So Virulent?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)

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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

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

Staphylococcus aureus is COAGULASE POSITIVE.

The other > 30 species of Staphylococcus (eg., S. epidermidis, & S. saprophyticus) are COAGULASE NEGATIVE.

Laboratory Identification

Negative

Slide Coagulase Test

(Positive)

Coagulase: Prothrombin-Like Substance Able to Clot Human or Rabbit Plasma.

Tube Coagulase Test

CATALASE TEST

H2O2 H2 + O2 (bubbling)

Slide catalase

Genus Staphylococcus is Catalase PositiveGenera Streptococcus & Enterococcus are Catalase Negative

Streptococcal Infections (Group A)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)• Spreading infections

Bacterial MeningitisCommon 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 Waterhouse-Frederichson 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-stainedsmears of CSF or upper respiratory specimens

• Culture on chocolate agar; unsupplementedsheep 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

InfectionsBy AnaerobicBacteria

Some Examples of Clinically Significant Anaerobe Infections

• 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)

Actinomycesfistula

“lumpy jaw”

Sulfur granule on Gram Stain

Actinomyces vs Nocardia in Pulmonary Specimens

NocardiaGram + Branchingfilaments

Nocardia;Modified-Kinyoun(acid-fast)

ActinoGram +

Actino:(not acid-Fast)

Anaerobic Aerobic

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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

65Acid-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

• 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.

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 interferon-

gamma, 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)

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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Reactivation TB (upper lobe)

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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• 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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