Respiratory Tract Infections

What structures make up the upper respiratory tract?

• Sinuses

• Nasal cavity

• Pharynx

• Epiglottis

• Larynx

What structures make up the lower respiratory tract?

• Trachea

• Bronchi

• Lungs

• Diaphragm

What are the mechanical defenses of the respiratory tract?

• Nasal hairs

• Mucus trapping microbes

• Cilia moving particles upward

What are the immune defenses of the respiratory tract?

• Complement

• Antimicrobial peptides

• Cytokines

• Macrophages

• Secretory IgA

What is the role of normal microbiota in the respiratory tract?

Prevent colonization by pathogens (microbial antagonism)

Where is most respiratory microbiota found?

Upper respiratory tract

Do lungs have microbiota?

Yes, but limited

Name normal biota that can become pathogenic

• Streptococcus pyogenes

• Haemophilus influenzae

• Streptococcus pneumoniae

• Neisseria meningitidis

• Staphylococcus aureus

• Candida albicans

What bacteria causes strep throat (pharyngitis)?

Streptococcus pyogenes

How is Streptococcus pyogenes transmitted?

• Respiratory droplets

• Direct contact

What are the virulence factors of Streptococcus pyogenes

• Specialized polysaccharides

• Lipoteichoic acid

• M protein

• Hyaluronic acid

How do surface antigens help Streptococcus pyogenes?

They mimic host proteins to help the bacteria avoid immune detection

How do specialized polysaccharides help Streptococcus pyogenes?

Protect the bacterium from being broken down by lysozyme

What does lipoteichoic acid do in Streptococcus pyogenes?

Helps the bacteria adhere to epithelial cells in the pharynx

What is the function of M protein in Streptococcus pyogenes?

Resists phagocytosis and helps with adherence

What does the hyaluronic acid capsule do in Streptococcus pyogenes?

Contributes to adhesiveness and helps the bacteria evade immunity

What can happen if streptococcal throat infections are untreated?

Scarlet fever and rheumatic fever can develop

What toxin causes scarlet fever produce?

Erythrogenic toxin

What are symptoms of Scarlet fever?

• Strawberry tongue

• Sandpaper-like rash with high fever

What is rheumatic fever caused by?

An immunologic cross-reaction between streptococcal M proteins and heart muscle

What are the extracellular toxins produced by Streptococcus pyogenes?

Streptolysins O and S, and erythrogenic toxin

What do streptolysins O and S do?

Cause beta-hemolysis on sheep blood agar

What does erythrogenic toxin cause?

A bright red rash and fever

How do some Streptococcus pyogenes strains gain the ability to produce erythrogenic toxin?

They acquire genes from a temperate bacteriophage

How are Streptococcus pyogenes infections rapidly diagnosed?

Rapid diagnostic tests using antibodies

Is there a vaccine for Streptococcus pyogenes?

No

How can Streptococcus pyogenes infections be prevented?

Good hygiene

What is the antibiotic of choice for Streptococcus pyogenes?

Penicillin

What antibiotic is used if a patient is allergic to penicillin?

Cephalexin

Why are antibiotics important even though many strep throat infections resolve on their own?

To prevent serious complications (sequelae)

What is another important bacterial cause of pharyngitis in adolescents and young adults?

Fusobacterium necrophorum

What type of organism is Fusobacterium necrophorum?

Anaerobic Gram-negative rod

What serious complication can Fusobacterium necrophorum cause?

Lemierre’s syndrome

What is Lemierre’s syndrome?

Formation of an infected blood clot (septic thrombophlebitis)

What is diphtheria?

An upper respiratory tract infection that causes pharyngitis

What structure forms in diphtheria infections?

A pseudomembrane

Can diphtheria affect the skin?

Yes, there is a cutaneous form

What is the causative agent of diphtheria?

Corynebacterium diphtheriae

What type of bacterium is Corynebacterium diphtheriae?

Gram-positive rod

How does Corynebacterium diphtheriae cause disease?

It inhibits protein synthesis

What symptoms help diagnose diphtheria?

• Fever

• Sore throat

• Pseudomembrane formation

Why are diphtheria cultures difficult to obtain?

Because of the pseudomembrane

What vaccine protects against diphtheria?

DTaP vaccine

What does DTaP stand for?

Diphtheria, tetanus, and acellular pertussis

What is the common cold?

An upper respiratory infection caused by many different viruses

What is the most common viral cause of the common cold?

Rhinoviruses

What other viruses can cause the common cold?

Coronavirus, adenovirus, and respiratory syncytial virus (RSV)

How is the common cold transmitted?

Indirect contact and droplet contact

What are common symptoms of the common cold?

Sneezing, scratchy throat, and runny nose

Who commonly develops fever with the common cold?

Children

What is sinusitis?

Inflammation or infection of the sinuses

What can cause sinusitis?

• Viruses

• Bacteria

• Fungi

• Allergies

How is bacterial sinusitis treated?

Broad-spectrum antibiotics

How is fungal sinusitis treated?

Antifungals and/or surgery

What is acute otitis media?

An ear infection involving inflammation of the eustachian tubes, fluid buildup in the middle ear, and bacterial growth in the fluid

What are common causative agents of acute otitis media?

• Streptococcus pneumoniae

• Candida auris

• Other bacteria or viruses

What vaccine helps prevent Streptococcus pneumoniae ear infections in infants?

Prevnar 13

How is acute otitis media treated?

Watchful waiting, antibiotics, or tympanic membrane tubes

What is otitis externa?

An infection or inflammation of the outer ear canal

What is another name for otitis externa?

Swimmer’s ear

What bacteria commonly cause swimmer’s ear?

Pseudomonas aeruginosa and Staphylococcus aureus

What is pneumonia?

Inflammation of the lungs where fluid fills the alveoli

What types of microbes can cause pneumonia?

Bacteria, fungi, and viruses

What is hospital-acquired pneumonia (HAP)?

Pneumonia acquired during a hospital stay

What bacteria commonly cause hospital-acquired pneumonia?

Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter species

What is ventilator-associated pneumonia (VAP)?

Pneumonia that develops in patients using mechanical ventilators

How can postoperative pneumonia risk be reduced?

• Deep breathing and frequent coughing

• Care of mechanical ventilators

• Empiric therapy

What is the most common cause of community-acquired pneumonia (CAP)?

Streptococcus pneumoniae

What organisms can cause community-acquired pneumonia?

• Streptococcus pneumoniae

• Legionella

• Mycoplasma pneumoniae

• Chlamydophila pneumoniae

• Histoplasma capsulatum

• Hantavirus

What is “walking pneumonia”?

A milder pneumonia commonly caused by Mycoplasma pneumoniae or Chlamydophila pneumoniae

Can influenza lead to pneumonia?

Yes, pneumonia can occur as a secondary infection after influenza

What type of bacterium is Streptococcus pneumoniae?

A Gram-positive bacterium that can be normal biota

What disease does Streptococcus pneumoniae cause?

Pneumococcal pneumonia

What symptoms are common in pneumococcal pneumonia?

Fever, chest pain, blood in sputum, and difficulty breathing

Who is especially at risk for pneumococcal pneumonia?

The elderly

How is Streptococcus pneumoniae identified in the lab?

It is optochin sensitive (P disk test)

Is Streptococcus pneumoniae usually sensitive to penicillin?

Yes

What vaccines help prevent Streptococcus pneumoniae infections?

Pneumovax 23 and Prevnar 13

Who receives Pneumovax 23?

Adults age 50 and older

Who receives Prevnar 13?

Children and adults

What causes Legionnaires’ disease?

Legionella pneumophila

What type of bacterium is Legionella pneumophila?

Gram-negative rod

Where is Legionella commonly found?

Tap water, cooling towers, spas, ponds, and freshwater systems

Why is Legionella difficult to control?

It is resistant to chlorine

How is Legionella spread?

Through aerosolized water droplets

What is Pontiac fever?

A mild, self-limiting upper respiratory disease caused by Legionella

What is Legionnaires’ disease?

A more serious pneumonia caused by Legionella

How are Mycoplasma and Chlamydophila pneumonia spread?

By aerosol droplets in close living quarters

Why is atypical pneumonia called “walking pneumonia”?

Most patients are not severely ill

What caused the hantavirus outbreak in the Four Corners area in 1993?

Exposure to infected rodents

How is hantavirus transmitted?

By inhaling airborne dust contaminated with rodent urine, feces, or saliva

What animals commonly spread hantavirus?

Deer mice

What fungus causes histoplasmosis?

Histoplasma capsulatum

Where is Histoplasma capsulatum commonly found?

Soils containing bird and bat droppings

What causes Pneumocystis pneumonia?

Pneumocystis jiroveci

Who commonly develops Pneumocystis pneumonia?

AIDS patients

How is Pneumocystis transmitted?

By inhalation of spores

Why are traditional antifungal drugs ineffective against Pneumocystis?

Because of the organism’s unusual cell wall chemistry

Are viral pneumonias usually severe?

No

What types of viruses cause influenza?

Influenza A, B, and C viruses